Phosphatic metabolites, intracellular pH and free [Mg2+] in single, intact porcine carotid artery segments studied by 31P-NMR

Superfused porcine carotid artery segments (approximately 7 cm lengths) were analyzed by 31P-NMR spectroscopic methods to characterize the 31P spectrum of arterial smooth muscle and to determine the influence of passive stretch (intraluminal pressurization, 95-100 mmHg) on cellular phosphatic metabolite levels, intracellular pH and free magnesium concentration ([Mg2+free]i). Equilibrated, single, intact arteries were studied under steady-state, constant flow conditions at 37 degrees C. Phosphoethanolamine, phosphocholine, inorganic phosphate (Pi), phosphocreatine (PCr) and nucleoside triphosphates (NTP), primarily ATP, were the principle metabolites detected in the 31P-NMR spectrum of intact arterial smooth muscle. The concentration of these metabolites and intracellular pH, as determined from the referenced chemical shift of Pi, were unaffected by pressurization. The PCr:Pi ratios determined for nonpressurized (flaccid) and pressurized arteries were 1.2 +/- 0.1 and 1.3 +/- 0.3, respectively. Intracellular pH averaged 7.02 +/- 0.02 (mean +/- 1 S.D.) for flaccid arteries vs. 7.03 +/- 0.05 for pressurized arteries. The upfield chemical shift of the beta-ATP peak, which has been described in other types of smooth muscle, was also observed in these experiments. Interestingly, pressurization significantly shifted the resonance position of this peak, which was interpreted to represent a change in [Mg2+free]i. The average [Mg2+free]i of flaccid artery preparations was computed to be 0.54 +/- 0.03 x 10(-3) M, as compared to 0.99 +/- 0.10 x 10(-3) M for pressurized arteries. This change in [Mg2+free]i was evident within the first hour following pressurization and persisted thereafter. These findings suggest that altering the resting length of vascular smooth muscle produces a change in [Mg2+free]i. This shift in free Mg2+ levels may act as a metabolic signal triggering a change in vascular smooth muscle metabolism, an effect which has been reported to occur in smooth muscle in response to stretch.     

Biomechanical properties of canine vertebral and internal carotid arteries

In order to understand the participation of the geometrical and elastic properties of the large cerebral arteries in the maintenance of brain circulatory homeostasis, biomechanical properties of isolated internal carotid artery (extracranial part) and vertebral artery (intrathoracic part) were investigated both in a relaxed and in an activated (3x 10(-6) mol.l-1 norepinephrine) state of the smooth muscle. Quasi-static large deformation mechanical test was carried out by means of changing the intraluminal pressure slowly (2.5 mmHg.sec-1) and cyclicly in a range of 0-250 mmHg at in vivo length while external diameter was recorded continuously as a function of the intraluminal pressure. Maximum active tangential strain was found to be -2.7 +/- 1.6% at 70 mmHg for the internal carotid artery, and -5.9 +/- 1.1% at 100 mmHg for the vertebral artery. Incremental elastic modulus decreased and distensibility increased in both arteries following smooth muscle activation, these alterations, however, were larger in the case of the vertebral artery. A U-shaped characteristic impedance of vertebral artery was found both in relaxed and in constricted states of this vessel. Minimum values for the relaxed and the activated segments were found at 90 mmHg and 120 mmHg, respectively. These results support the hypothesis that certain biomechanical properties of the large arteries, like impedance, can be regarded as controlled variables that may contribute to the optimization of circulatory functions.     

Vascular and metabolic response to isolated small muscle mass exercise: effect of age

To determine the effect of age on quadriceps muscle blood flow (QMBF), leg vascular resistance (LVR), and maximum oxygen uptake (QVO2 max), a thermal dilution technique was used in conjunction with arterial and venous femoral blood sampling in six sedentary young (19.8 +/- 1.3 yr) and six sedentary old (66.5 +/- 2.1 yr) males during incremental knee extensor exercise (KE). Young and old attained a similar maximal KE work rate (WRmax) (young: 25.2 +/- 2.1 and old: 24.1 +/- 4 W) and QVO2 max (young: 0.52 +/- 0.03 and old: 0.42 +/- 0.05 l/min). QMBF during KE was lower in old subjects by approximately 500 ml/min across all work rates, with old subjects demonstrating a significantly lower QMBF/W (old: 174 +/- 20 and young: 239 +/- 46 ml. min-1. W-1). Although the vasodilatory response to incremental KE was approximately 142% greater in the old (young: 0.0019 and old: 0.0046 mmHg. min. ml-1. W-1), consistently elevated leg vascular resistance (LVR) in the old, approximately 80% higher LVR in the old at 50% WR and approximately 40% higher LVR in the old at WRmax (young: 44.1 +/- 3.6 and old: 31.0 +/- 1.7 mmHg. min. ml-1), dictated that during incremental KE the LVR of the old subjects was never less than that of the young subjects. Pulse pressures, indicative of arterial vessel compliance, were approximately 36% higher in the old subjects across all work rates. In conclusion, well-matched sedentary young and old subjects with similar quadriceps muscle mass achieved a similar WRmax and QVO2 max during incremental KE. The old subjects, despite a reduced QMBF, had a greater vasodilatory response to incremental KE. Given that small muscle mass exercise, such as KE, utilizes only a fraction of maximal cardiac output, peripheral mechanisms such as consistently elevated leg vascular resistance and greater pulse pressures appear to be responsible for reduced blood flow persisting throughout graded KE in the old subjects.     

Measurements of mouse pulmonary artery biomechanics

BACKGROUND: Robust techniques for characterizing the biomechanical properties of mouse pulmonary arteries will permit exciting gene-level hypotheses regarding pulmonary vascular disease to be tested in genetically engineered animals. In this paper, we present the first measurements of the biomechanical properties of mouse pulmonary arteries. METHOD OF APPROACH: In an isolated vessel perfusion system, transmural pressure, internal diameter and wall thickness were measured during inflation and deflation of mouse pulmonary arteries over low (5-40 mmHg) and high (10-120 mmHg) pressure ranges representing physiological pressures in the pulmonary and systemic circulations, respectively. RESULTS: During inflation, circumferential stress versus strain showed the nonlinear "J"-shape typical of arteries. Hudetz's incremental elastic modulus ranged from 27 +/- 13 kPa (n = 7) during low-pressure inflation to 2,700 +/- 1,700 kPa (n = 9) during high-pressure inflation. The low and high-pressure testing protocols yielded quantitatively indistinguishable stress-strain and modulus-strain results. Histology performed to assess the state of the tissue after mechanical testing showed intact medial and adventitial architecture with some loss of endothelium, suggesting that smooth muscle cell contractile strength could also be measured with these techniques. CONCLUSIONS: The measurement techniques described demonstrate the feasibility of quantifying mouse pulmonary artery biomechanical properties. Stress-strain behavior and incremental modulus values are presented for normal, healthy arteries over a wide pressure range. These techniques will be useful for investigations into biomechanical abnormalities in pulmonary vascular disease.     

Viscoelastic properties of isolated rat colon smooth muscle cells

The measurement of the biomechanical properties of gastrointestinal smooth muscle cells is important for the basic understanding of digestive function and the interaction of muscle cells with the matrix. Externally applied forces will deform the cells depending upon their mechanical properties. Hence, the evoked response mediated through stretch-sensitive ion-channels in the smooth muscle cell membrane will depend upon membrane properties and the magnitude of the external force. The aim of this study was to test the hypothesis that gastrointestinal smooth muscle cells behave in a viscoelastic manner. Smooth muscle cells were dissociated from the muscle layers of the descending colon. The viscoelastic properties of the isolated cells were characterized by measuring the mechanical deflection response of the cell membrane to a negative pressure of 1cm H(2)O applied across the cell through a micropipette and fitting the response to a theoretical viscoelastic solid model. The viscoelastic mechanical constants of the isolated cells (N=9) were found to be as follows: k(1)=19.99+/-2.86 Pa, k(2)=7.19+/-1.21 Pa, mu=25.36+/-6.14 Pas and tau=4.84+/-0.95 s. This study represents, to the best of our knowledge, the first quantitative mechanical properties of isolated living smooth muscle cells from the gastrointestinal tract. The mechanical properties determined in this study will be of use in future analytical and numerical smooth muscle cell models to better predict the mechanism between the magnitude of mechanical stimuli, mechanosensitivity and the evoked afferent responses.     

Inhibition of vascular smooth muscle cell proliferation and intimal hyperplasia by gene transfer of beta-interferon.

BACKGROUND: Balloon injury of the arterial wall induces increased vascular smooth cell proliferation, enhanced elastic recoil, and abnormalities in thrombosis, each of which contribute to regrowth of intima and the lesion of restenosis. Several gene transfer approaches have been used to inhibit such intimal smooth muscle cell growth. In this report, adenoviral gene transfer of beta-interferon (beta-IFN) was analyzed in a porcine model of balloon injury to determine whether a secreted growth inhibitory protein might affect the regrowth of vascular smooth muscle cells in vitro and in arteries. MATERIALS AND METHODS: An adenoviral vector encoding beta-interferon (ADV-beta-IFN) was prepared and used to infect porcine vascular smooth muscle cells in a porcine balloon injury model. Its antiproliferative effect was analyzed in vitro and in vivo. RESULTS: Expression of recombinant porcine beta-IFN in vascular smooth muscle cells reduced cell proliferation significantly in vitro, and supernatants derived from the beta-IFN vector inhibited vascular smooth muscle cell proliferation relative to controls. When introduced into porcine arteries after balloon injury, a reduction in cell proliferation was observed 7 days after gene transfer measured by BrdC incorporation (ADV-delta E1 arteries 14.5 +/- 1.2%, ADV-beta IFN 6.8 +/- 0.8%, p < 0.05, unpaired, two-tailed t-test). The intima-to-media area ratio was also reduced (nontransfected arteries, 0.70 +/- 0.05; ADV-delta E1 infected arteries, 0.69 +/- 0.06; ADV-beta-IFN infected arteries, 0.53 +/- 0.03; p < 0.05, ANOVA with Dunnett t-test). No evidence of organ toxicity was observed, and regrowth of the endothelial cell surface was observed 3-6 weeks after balloon injury. CONCLUSIONS: Gene transfer of an adenoviral vector encoding beta-IFN into balloon-injured arteries reduced vascular smooth muscle proliferation and intimal formation. Expression of this gene product may have potential application for the treatment of vascular proliferative diseases.     

Comparison of incremental and steady state tests of endurance training

To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditioning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70-80% VO2max. Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % VO2max, increased with training by 17% (p less than 0.01) and 9% (p less than 0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% VO2max) to a blood lactate steady state (4.8 +/- 1.4 mmol.l-1) whereas, after training, AeT intensity (73% VO2max) led to a blood lactate accumulation of up to 6.6 +/- 1.7 mmol.l-1 without significant modification of muscle lactate (7.6 +/- 3.1 and 8.2 +/- 2.8 mmol.kg-1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

A simple model describing the elastic properties of human umbilical arterial smooth muscle

Elastic properties of cylindrical segments of 71 normal double and 4 single human umbilical arteries were studied. This specimen is rich in vascular smooth muscle in comparison with other great arteries. Outer diameter versus intraluminal pressure characteristic curves were taken with decreasing pressures in vitro in different contraction states. Tangential force and circumferential incremental elastic modulus were computed. A sum of 222 curves was analysed. The investigations showed that if we take tangential force and outer radius values measured at the same pressure levels but in different contraction states, then a similar proportional change in tangential force will induce a similar proportional passive change in the outer radius, to some extent independently of the degree of active tangential shortening of the segment. For example to induce a 10% passive decrease of the outer radius from values measured at 100 mm Hg intraluminal pressure, tangential force had to be decreased by 76.7 +/- 9.9% in single relaxed arteries, and by 79.6 +/- 0.8% in normal double relaxed segments. These values corresponded to intraluminal pressure levels of 26.4 +/- 4.9 mm Hg and 23.1 +/- 0.9 mm Hg, respectively. In 30% active spontaneous shortening to reach the same 10% passive decrease in outer radius from the value measured at 100 mm Hg, tangential force had to be decreased by 75.2 +/- 1.9% which corresponded to 29.6 +/- 20 mm Hg. The same values in 5-HT induced contraction, 30% active shortening were 76.7 +/- 2.0% and 28.4 +/- 2.6 mm Hg, respectively. In addition to the similarity of relative changes in tangential force, the pressure levels were to some extent also similar. These data suggest that elastic elements in the human umbilical arterial smooth muscle may be organized in such a way as to ensure similar prestretch of similar elastic elements at similar pressures independently of the degree of active shortening of the circumference.     

31P nuclear magnetic resonance spectroscopy study of the anaerobic threshold in humans

The relationships among the lactate threshold (LT), ventilatory threshold (VT), and intracellular biochemical events in exercising muscle have not been well defined. Therefore 14 normal subjects performed incremental plantar flexion to exhaustion on 2 study days, the first for determination of LT and VT and the second for continuous 31P nuclear magnetic resonance spectroscopy of calf muscle. Exercising calf muscle pH fell precipitously at 66.4 +/- 3.4% (SE) of the maximum O2 uptake (VO2max) and was termed the intramuscular pH threshold. This did not occur at a significantly different metabolic rate from that at the LT (78.6 +/- 5.9% VO2max) or at the VT (75.0 +/- 4.1% VO2max, P = 0.15 by analysis of variance). Four subjects showed an intramuscular pH threshold and VT without a perceptible rise in forearm venous blood lactate. It is concluded that traditional markers of the "anaerobic threshold," the LT and VT, occur as intramuscular pH becomes acid for a group of normal subjects undergoing incremental exercise to exhaustion. It is speculated that neuronal pathways linking intramuscular biochemical events to the ventilatory control center may explain the intact VT in those subjects without an "intermediary" LT.     

Insulin resistance does not impair contractile responses of cerebral arteries

Insulin resistance (IR) impairs endothelium-mediated vasodilation in cerebral arteries as well as K+ channel function in vascular smooth muscle. Peripheral arteries also show an impaired endothelium-dependent vasodilation in IR and concomitantly show an enhanced contractile response to endothelin-1 (ET-1). However, the contractile responses of the cerebral arteries in IR have not been examined systematically. This study examined the contractile responses of pressurized isolated middle cerebral arteries (MCAs) in fructose-fed IR and control rats. IR MCAs showed no difference in pressure-mediated (80 mmHg) vasoconstriction compared to controls, either in time to develop spontaneous tone (control: 61+/-3 min, n=30; IR: 63+/-2 min, n=26) or in the degree of that tone (control: 60 min: 33+/-2%, n=22 vs. IR 60 min: 34+/-3%, n=17). MCAs treated with ET-1 (10(-8.5) M) constrict similarly in control (53+/-3%, n=14) and IR (53+/-3%, n=14) arteries. Constrictor responses to U46619 (10(-6) M) are also similar in control (48+/-9%, n=8) and IR (42+/-5%, n=6) MCAs as are responses to extraluminal uridine 5'-triphosphate (UTP; 10(-4.5) M) (control: 35+/-7%, n=11 vs. IR: 38+/-3%, n=10). These findings demonstrate that constrictor responses remain intact in IR despite a selective impairment of dilator responses and endothelial and vascular smooth muscle K+ channel function in cerebral arteries. Thus, it appears that the increased susceptibility to cerebrovascular abnormalities associated with IR and diabetes (including cerebral ischemia, stroke, vertebrobasilar transient ischemic attacks) is not due to an enhanced vasoreactivity to constrictor agents.     

Effect of pedaling rates and myosin heavy chain composition in the vastus lateralis muscle on the power generating capability during incremental cycling in humans

In this study, we have determined power output reached at maximal oxygen uptake during incremental cycling exercise (P(I, max)) performed at low and at high pedaling rates in nineteen untrained men with various myosin heavy chain composition (MyHC) in the vastus lateralis muscle. On separate days, subjects performed two incremental exercise tests until exhaustion at 60 rev min(-1) and at 120 rev min(-1). In the studied group of subjects P(I, max) reached during cycling at 60 rev min(-1) was significantly higher (p=0.0001) than that at 120 rev min(-1) (287+/-29 vs. 215+/-42 W, respectively for 60 and 120 rev min(-1)). For further comparisons, two groups of subjects (n=6, each) were selected according to MyHC composition in the vastus lateralis muscle: group H with higher MyHC II content (56.8+/-2.79 %) and group L with lower MyHC II content in this muscle (28.6+/-5.8 %). P(I, max) reached during cycling performed at 60 rev min(-1) in group H was significantly lower than in group L (p=0.03). However, during cycling at 120 rev min(-1), there was no significant difference in P(I, max) reached by both groups of subjects (p=0.38). Moreover, oxygen uptake (VO(2)), blood hydrogen ion [H(+)], plasma lactate [La(-)] and ammonia [NH(3)] concentrations determined at the four highest power outputs completed during the incremental cycling performed at 60 as well as 120 rev min(-1), in the group H were significantly higher than in group L. We have concluded that during an incremental exercise performed at low pedaling rates the subjects with lower content of MyHC II in the vastus lateralis muscle possess greater power generating capabilities than the subjects with higher content of MyHC II. Surprisingly, at high pedaling rate, power generating capabilities in the subjects with higher MyHC II content in the vastus lateralis muscle did not differ from those found in the subjects with lower content of MyHC II in this muscle, despite higher blood [H(+)], [La(-)] and [NH(3)] concentrations. This indicates that at high pedaling rates the subjects with higher percentage of MyHC II in the vastus lateralis muscle perform relatively better than the subjects with lower percentage of MyHC II in this muscle.     

A novel bronchial ring bioassay for the evaluation of small airway smooth muscle function in mice

Advances in our understanding of murine airway physiology have been hindered by the lack of suitable, ex vivo, small airway bioassay systems. In this study, we introduce a novel small murine airway bioassay system that permits the physiological and pharmacological study of intrapulmonary bronchial smooth muscle via a bronchial ring (BR) preparation utilizing BR segments as small as 200 microm in diameter. Using this ex vivo BR bioassay, we characterized small airway smooth muscle contraction and relaxation in the presence and absence of bronchial epithelium. In control BRs, the application of mechanical stretch is followed by spontaneous bronchial smooth muscle relaxation. BRs pretreated with methacholine (MCh) partially attenuate this stretch-induced relaxation by as much as 42% compared with control. MCh elicited a dose-dependent bronchial constriction with a maximal tension (E(max)) of 8.7 +/- 0.2 mN at an EC(50) of 0.33 +/- 0.02 microM. In the presence of nifedipine, ryanodine, 2-aminoethoxydiphenyl borate, and SKF-96365, E(max) to MCh was significantly reduced. In epithelium-denuded BRs, MCh-induced contraction was significantly enhanced to 11.4 +/- 1.0 mN with an EC(50) of 0.16 +/- 0.04 microM (P < 0.01). Substance P relaxed MCh-precontracted BR by 62.1%; however, this bronchial relaxation effect was completely lost in epithelium-denuded BRs. Papaverine virtually abolished MCh-induced constriction in both epithelium-intact and epithelium-denuded bronchial smooth muscle. In conclusion, this study introduces a novel murine small airway BR bioassay that allows for the physiological study of smooth muscle airway contractile responses that may aid in our understanding of the pathophysiology of asthma.     

Force-velocity relationships in hypertensive arterial smooth muscle

Increased total peripheral resistance is the cardinal haemodynamic disorder in essential hypertension. This could be secondary to alterations in the mechanical properties of vascular smooth muscle. Adequate study has not been made of the force-velocity (F-V) relationship in hypertensive arterial smooth muscle. Increased shortening in arterial smooth muscle would result in greater narrowing of arteries. The objectives of this investigation were to see if there is (i) increased shortening or increased maximum change in muscle length (delta Lmax where L stands for muscle length), (ii) an increased maximum velocity of shortening (Vmax) measured in l omicron per second where l omicron is the optimal muscle length for tension development, and (iii) a difference in maximum isometric tension (P omicron) developed in spontaneously hypertensive rat (SHR; N = 6) compared with normotensive Wistar Kyoto rat (WKY;N = 5) caudal artery strips. An electromagnetic muscle lever was employed in recording force-velocity data. Analysis of these data revealed the following: (a) the SHR mean P omicron of 6.21 +/- 1.01 N/cm2 was not different from the mean WKY P omicron of 6.97 +/- 1.64 N/cm2 (p greater than 0.05); (b) the SHR preparations showed greater shortening for all loads imposed; (c) the SHR Vmax of 0.016 l omicron/s was greater than the WKY Vmax of 0.013 l omicron/s (p less than 0.05). This study provides evidence that while hypertensive arterial smooth muscle is not able to produce more force than normotensive arterial smooth muscle, it is capable of faster and greater shortening. The latter could result in increased narrowing of hypertensive arteries and increased blood pressure.     

Changes in biophysical and biochemical properties of single bronchial smooth muscle cells from asthmatic subjects

Whether contractility of bronchial smooth muscle cells (BSMC) from asthmatic subjects is significantly altered has never been validated. We tested the hypothesis that such BSMC show increased contractility. Cells were isolated from endobronchial biopsies. BSMC shortening was measured under an inverted microscope. Statistically significant increases in maximum shortening capacity (Delta L max) and velocity (Vo) were found in asthmatic BSMC compared with normal cells. Mean Delta L max in asthmatic BSMC was 39.05 +/- 1.99% (SE) of resting cell length compared with 28.6 +/- 1.1% in normal cells; mean Vo was 7.2 +/- 0.8% of resting cell length/s in asthmatic cells and 5.23 +/- 0.46% in normal cells. To investigate the mechanism of the increased contractility, we measured mRNA abundance of smooth muscle types of myosin light chain kinase (smMLCK) and myosin heavy chain. RT-PCR data revealed that smMLCK mRNA was higher in asthmatic BSMC (0.106 +/- 0.021 arbitrary densitometric units, n = 7) than in control cells (0.04 +/- 0.008, n = 11; P < 0.05). Messages for myosin heavy chain isoforms showed no difference. Increased kinase message content is an index of the mechanism for the increased velocity and capacity of shortening we report.     

Effect of different cycling frequencies during incremental exercise on the venous plasma potassium concentration in humans

The effect of different muscle shortening velocity was studied during cycling at a pedalling rate of 60 and 120 rev.min(-1) on the [K+]v in humans. Twenty-one healthy young men aged 22.5+/-2.2 years, body mass 72.7+/-6.4 kg, VO2 max 3.720+/-0.426 l. min(-1), performed an incremental exercise test until exhaustion. The power output increased by 30 W every 3 min, using an electrically controlled ergometer Ergoline 800 S (see Zoladz et al. J. Physiol. 488: 211-217, 1995). The test was performed twice: once at a cycling frequency of 60 rev.min(-1) (test A) and a few days later at a frequency of 120 rev. min(-1) (test B). At rest and at the end of each step (i.e. the last 15 s) antecubital venous blood samples for [K+]p were taken. Gas exchange variables were measured continuously (breath-by-breath) using Oxycon Champion Jaeger. The pre-exercise [K+]v in both tests was not significantly different amounting to 4.24+/-0.36 mmol.l(-1) in test A, and 4.37+/-0.45 mmol.l(-1) in test B. However, the [K+]p during cycling at 120 rev. min(-1) was significantly higher (p<0.001, ANOVA for repeated measurements) at each power output when compared to cycling at 60 rev.min(-1). The maximal power output reached 293+/-31 W in test A which was significantly higher (p<0.001) than in test B, which amounted to 223+/-40 W. The VO2max values in both tests reached 3.720+/-0.426 l. min(-1) vs 3.777+/-0.514 l. min(-1). These values were not significantly different. When the [K+]v was measured during incremental cycling exercise, a linear increase in [K+]v was observed in both tests. However, a significant (p<0.05) upward shift in the [K+]v and a % VO2max relationship was detected during cycling at 120 rev.min(-1). The [K+]v measured at the VO2max level in tests A and B amounted to 6.00+/-0.47 mmol.l-1 vs 6.04+/-0.41 mmol.l-1, respectively. This difference was not significant. It may thus be concluded that: a) generation of the same external mechanical power output during cycling at a pedalling rate of 120 rev.min(-1) causes significantly higher [K+]v changes than when cycling at 60 rev.min(-1), b) the increase of venous plasma potassium concentration during dynamic incremental exercise is linearly related to the metabolic cost of work expressed by the percentage of VO2max (increase as reported previously by Vollestad et al. J. Physiol. 475: 359-368, 1994), c) there is a tendency towards upward up shift in the [K+]v and % VO2max relation during cycling at 120 rev.min(-1) when compared to cycling at 60 rev.min(-1).     

Inhibition of PGI2 signaling by miconazole in vascular smooth muscle cells

Miconazole is widely used clinically as an anti-fungal agent and experimentally as a cytochrome P450 (CYP) inhibitor. In rat coronary arteries that produce PGI(2) as the major arachidonic acid (AA) metabolite, activation of the large-conductance K(+) (BK) channels in coronary arterial smooth muscle cells by AA was inhibited by miconazole but not by the CYP inhibitor SKF525A. Activation of BK currents in coronary smooth muscle cells by carbacyclin or iloprost also was inhibited by miconazole but not by SKF525A, suggesting that miconazole might have properties other than those of CYP inhibition. In addition, carbacyclin-induced dilation of isolated mesenteric arteries was inhibited by treatment with miconazole (51.9+/-4.2% dilation in control, n=7 versus 30.1+/-4.0% with miconazole, n=4, p<0.005) but not SKF525A (52.8+/-3.6%, n=8). In contrast, miconazole did not affect BK channel activation and vasodilation produced by the phosphodiesterase inhibitor RO-201724. In cultured coronary smooth muscle cells, carbacyclin (1microM) stimulated cAMP production by 22-fold (183+/-29pmol/mg at baseline, 4062+/-212pmol/mg with carbacyclin, n=3, p<0.001). The carbacyclin effect was significantly attenuated by treatment with miconazole (1542+/-201pmol/mg, n=3, p<0.001 versus carbacyclin alone), but not by SKF525A (3460+/-406pmol/mg, n=3, p=NS versus carbacyclin alone). These results indicate that in addition to its CYP inhibition properties, miconazole inhibits PGI(2) signaling. Hence, experiments using miconazole as a CYP inhibitor should be interpreted with caution.     

Tensiometric study of muscular strips of guinea pig gallbladder

The tensiometric properties of smooth muscle strips from 10 male guinea pig gallbladders were evaluated following acetylcholine (ACH), cholecystokinin octapeptide (CCK-OP), cerulein (CRL) and histamine (HIS) administration. All agonists induced dose-dependent tonic contractions with the maximum effect caused by the octapeptide. CRL showed a 9-folds higher relative potency when compared to CCK-OP. ED50s of agonists were: ACH 1.36 +/- 0.28 SEM microM (n = 14; range 0.20-3.60); HIST, 5.7 +/- 1.9 microM (n = 12; range 1-23); CRL 0.72 +/- 0.15 nM (n = 8; range 0.35-1.07); CCK-OP, 6.77 +/- 1.80 nM (n = 12; range 0.44-20.32); For the same strips, max tension (g), was: 1.97 (SEM 0.12) for ACH; 1.5 (0.18) for HIST; 1.81 (0.18) for CRL; 2.44 (0.14) for CCK-OP. Pretreatment of the strips with atropine (1 microM) completely abolished ACh-induced contractions, without affecting either CCK-OP or CRL responses. The model represents a valid "in vitro" study of different molecules whose action might stimulate, enhance or inhibit the physiological hormonal and non-hormonal effect of the agonists at the level of animal and human gallbladder smooth muscle.     

Selective transport of adenosine into porcine coronary smooth muscle

Adenosine (ADO), an endogenous regulator of coronary vascular tone, enhances vasorelaxation in the presence of nucleoside transport inhibitors such as dipyridamole. We tested the hypothesis that coronary smooth muscle (CSM) contains a high-affinity transporter for ADO. ADO-mediated relaxation of isolated large and small porcine coronary artery rings was enhanced 12-fold and 3.4-fold, respectively, by the transport inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI). Enhanced relaxation was independent of endothelium and was selective for ADO over synthetic analogs. Uptake of [(3)H]ADO into freshly dissociated CSM cells or endothelium-denuded rings was linear and concentration dependent. Kinetic analysis yielded a maximum uptake (V(max)) of 67 +/- 7.0 pmol. mg protein(-1). min(-1) and a Michaelis constant (K(m)) of 10. 5 +/- 5.8 microM in isolated cells and a V(max) of 5.1 +/- 0.5 pmol. min(-1). mg wet wt(-1) and a K(m) of 17.6 +/- 2.6 microM in intact rings. NBTI inhibited transport into small arteries (IC(50) = 42 nM) and cells. Analyses of extracellular space and diffusion kinetics using [(3)H]sucrose indicate the V(max) and K(m) for ADO transport are sufficient to clear a significant amount of extracellular adenosine. These data indicate CSM possess a high-affinity nucleoside transporter and that the activity of this transporter is sufficient to modulate ADO sensitivity of large and small coronary arteries.     

High content of MYHC II in vastus lateralis is accompanied by higher VO2/power output ratio during moderate intensity cycling performed both at low and at high pedalling rates.

The aim of this study was to examine the relationship between the content of various types of myosin heavy chain isoforms (MyHC) in the vastus lateralis muscle and pulmonary oxygen uptake during moderate power output incremental exercise, performed at low and at high pedalling rates. Twenty one male subjects (mean +/- SD) aged 24.1 +/- 2.8 years; body mass 72.9 +/- 7.2 kg; height 179.1 +/- 4.8 cm; BMI 22.69 +/- 1.89 kg.m(-2); VO2max 50.6 +/- 5.3 ml.kg.min(-1), participated in this study. On separate days, they performed two incremental exercise tests at 60 rev.min(-1) and at 120 rev.min(-1), until exhaustion. Gas exchange variables were measured continuously breath by breath. Blood samples were taken for measurements of plasma lactate concentration prior to the exercise test and at the end of each step of the incremental exercise. Muscle biopsies were taken from the vastus lateralis muscle, using Bergstr?m needle, and they were analysed for the content of MyHC I and MyHC II using SDS--PAGE and two groups (n=7, each) were selected: group H with the highest content of MyHC II (60.7 % +/- 10.5 %) and group L with the lowest content of MyHC II (27.6 % +/- 6.1 %). We have found that during incremental exercise at the power output between 30-120 W, performed at 60 rev.min(-1), oxygen uptake in the group H was significantly greater than in the group L (ANCOVA, p=0.003, upward shift of the intercept in VO2/power output relationship). During cycling at the same power output but at 120 rev.min(-1), the oxygen uptake was also higher in the group H, when compared to the group L (i.e. upward shift of the intercept in VO2/power output relationship, ANCOVA, p=0.002). Moreover, the increase in pedalling rate from 60 to 120 rev.min(-1) was accompanied by a significantly higher increase of oxygen cost of cycling and by a significantly higher plasma lactate concentration in subjects from group H. We concluded that the muscle mechanical efficiency, expressed by the VO2/PO ratio, during cycling in the range of power outputs 30-120 W, performed at 60 as well as 120 rev.min(-1), is significantly lower in the individuals with the highest content of MyHC II, when compared to the individuals with the lowest content of MyHC II in the vastus lateralis.     

Aging attenuates vascular and metabolic plasticity but does not limit improvement in muscle VO(2) max

The interactions between exercise, vascular and metabolic plasticity, and aging have provided insight into the prevention and restoration of declining whole body and small muscle mass exercise performance known to occur with age. Metabolic and vascular adaptations to normoxic knee-extensor exercise training (1 h 3 times a week for 8 wk) were compared between six sedentary young (20 +/- 1 yr) and six sedentary old (67 +/- 2 yr) subjects. Arterial and venous blood samples, in conjunction with a thermodilution technique facilitated the measurement of quadriceps muscle blood flow and hematologic variables during incremental knee-extensor exercise. Pretraining, young and old subjects attained a similar maximal work rate (WR(max)) (young = 27 +/- 3, old = 24 +/- 4 W) and similar maximal quadriceps O(2) consumption (muscle Vo(2 max)) (young = 0.52 +/- 0.03, old = 0.42 +/- 0.05 l/min), which increased equally in both groups posttraining (WR(max), young = 38 +/- 1, old = 36 +/- 4 W, Muscle Vo(2 max), young = 0.71 +/- 0.1, old = 0.63 +/- 0.1 l/min). Before training, muscle blood flow was approximately 500 ml lower in the old compared with the young throughout incremental knee-extensor exercise. After 8 wk of knee-extensor exercise training, the young reduced muscle blood flow approximately 700 ml/min, elevated arteriovenous O(2) difference approximately 1.3 ml/dl, and increased leg vascular resistance approximately 17 mmHg x ml(-1) x min(-1), whereas the old subjects revealed no training-induced changes in these variables. Together, these findings indicate that after 8 wk of small muscle mass exercise training, young and old subjects of equal initial metabolic capacity have a similar ability to increase quadriceps muscle WR(max) and muscle Vo(2 max), despite an attenuated vascular and/or metabolic adaptation to submaximal exercise in the old.