Relationships between voltage and tension in sheep cardiac Purkinje fibers

The two-microelectrode technique of voltage clamping sheep cardiac Purkinje fibers was used to examine the changes in contraction which occur during trains of voltage clamps. (A "train" is defined as a series of voltage clamps delivered at a particular rate, beginning after a rest long enough that the effects of previous stimulation have died away.) Contractions showed striking staircases, or progressive changes in peak isometric tension, during trains. Short clamps, clamps to voltages more negative than --20 or --30 mV, or holding potentials less negative than the resting potential favored negative staircases, while long clamps, clamps to positive voltages, and holding potentials near the resting potential each favored positive staircases. The staircase behavior appeared to be due to changes in the initial rate of recovery of the ability to contract. The changes in staircase behavior as a function of clamp voltage suggested that the relationship between peak tension and clamp voltage should depend on the experimental design. When the steady-state contraction was plotted as a function of clamp voltage, voltage-tension relations like those recently reported for working ventricle were obtained, with a threshold between --30 and - -40 mV and a steep relation between tension and voltage. When the first contraction after a rest was plotted, the threshold voltage was more negative, the curve was flatter, and the peak tensions at inside positive voltages were reduced.     

Relationship between oxygen tension, coronary vasodilation and prostaglandin biosynthesis in the isolated rabbit heart

In isolated perfused rabbit hearts, coronary vasodilation, produced by reduced oxygen tension seems to be independent of myocardial prostaglandin biosynthesis. a) Anoxia (N₂: CO₂ 95: 5%) produced coronary vasodilation without causing prostaglandin-like substance (PLS) biosynthesis and release; b) the decrease in coronary resistance during hypoxia (N₂:O₂:CO₂ — 80:15:5 %) was sustained during myocardial perfusion with the low oxygen media despite the transitory nature of its PLS release; and c) indomethacin, which abolished basal or ADP stimulated myocardial PLS release, did not abolish the coronary vasodilation produced by ischemia, hypoxia, or anoxia.     

Relationships between embolism,stem water tension,and diameter changes

A model for embolism in the sapflow process was developed, in which embolism is described as a physical process linked to real physical properties of the conduits and the thermodynamic state of water. Different mechanisms leading to embolism and their effect on water relations and especially diurnal diameter changes in a tree were examined. The mechanisms of heterogeneous nucleation, air-seeding, and bubble growth have been considered. The significance of embolism has been revealed here by examining diameter changes, which is an easily measurable quantity under field conditions. The most fundamental effects of embolism on sapflow are decrease in permeability and release of water from embolizing conduits to the transpiration stream. These can be indirectly detected by observing diameter changes. If possible changes in elasticity are not accounted for, embolism generally tends to enhance the amplitude of the diurnal diameter changes due to reduced permeability and increased tensions. In the case of reduced elasticity, embolism gives rise to smaller amplitudes of diameter changes.     

Neuropeptide Y modulates the action of vasodilator agents in guinea-pig epicardial coronary arteries

Recently, we have demonstrated that guinea-pig epicardial coronary arteries are supplied by numerous nerve fibres containing neuropeptide Y (NPY) immunoreactivity. However, examination of vasomotor responses revealed that NPY did not elicit a contractile response in these arteries. In contrast, acetylcholine (ACh), calcitonin gene-related peptide (CGRP), substance P and vasoactive intestinal polypeptide (VIP) all relaxed precontracted arteries. In the present study, we have used histochemical, immunohistochemical and in vitro pharmacological techniques, in order to further investigate the possible role of NPY in guinea-pig epicardial coronary arteries. A double-immunofluorescence staining technique revealed that CGRP and substance P were co-localized in nerve fibres distinct from those displaying NPY immunoreactivity. Furthermore, using a method combining immunofluorescence and histochemical techniques, we observed that putative cholinergic nerve fibres (identified by their acetylcholinesterase content) and NPY-immunoreactive nerve fibres are two different nerve populations. An in vitro pharmacological method demonstrated that NPY markedly inhibited the relaxant responses mediated by ACh, VIP, substance P and isoprenaline but had no effect on CGRP. These results suggest that NPY-containing nerves associated with guinea-pig epicardial coronary arteries may be predominantly involved in modulating the action of vasodilator agents.     

Relationships between burn size,immunosuppression, and macrophage hyperactivity in a murine model of thermal injury

Burn injury induces immune dysfunction and alters numerous physiological parameters. While clinical studies indicate that burn injury size profoundly impacts patient immune status, only limited experimental studies have systematically addressed its impact on immune functional parameters. In the present study, mice were subjected to burn injuries of varying sizes and splenic immune cells (splenocytes and macrophages) were isolated 7 days thereafter. Burn injury suppressed splenic T-cell proliferation in an injury size-dependent manner that correlated with the release of the immunosuppressive mediators PGE(2) and nitric oxide. In addition, a shift towards an immunosuppressive Th-2 cytokine profile and a hyperactive macrophage phenotype (increased release of inflammatory mediators) was observed post-injury, however, this effect was in part independent of burn size. Thus, unlike patient survival data, burn injury-induced changes in immune function do not necessarily correlate with the size of the injury.     

The autoregulation of intracellular oxygen tension and the modification of cellular radiosensitivity. The development of an adaptation hypothesis

A hypothesis is reported postulating that the range within which the intracellular oxygen content varies with changes in the external oxygenation conditions is responsible for the oxygen-dependent radiosensitivity modification that may be controlled by the diffusion resistance of a cytoplasmic membrane. The adaptation mechanism of intracellular Po2 autoregulation is involved when drastic changes in the oxygen content of the environment occur. As the oxygen content decreases this mechanism provides maximal values of the intracellular Po2 required for optimizing cell viability; the increased oxygen content prevents cells from oxygen intoxication.     

Relationship between cytosolic calcium and oxygen consumption in isolated rat hearts.

Maximum oxygen consumption was attained in isolated perfused rat hearts using high perfusate calcium and/or isoproterenol, or phenylephrine. The amplitude of calcium transients was directly related to oxygen consumption until oxygen consumed per beat reached maximum. At saturating oxygen consumption the amplitude of [Ca2+]i transients continued to increase, indicative of a calcium overload. In all cases +dP/dt correlated proportionately with +dCa2+/dt. Augmented developed pressure, related to isoproterenol-induced increase in cytosolic cAMP, cannot be attributed totally to elevated levels of [Ca2+]i transients. Adenosine (10(-5) M) added to the medium containing isoproterenol (10(-6) M) negated the isoproterenol-induced increase in cAMP and returned cardiac performance, oxygen consumption, and amplitude of [Ca2+]i transients to control state.     

Relationships among pressure, tension, and shape of the diaphragm

The shape of the diaphragm dome was calculated from transdiaphragmatic pressure and tension in the diaphragm. It was assumed that the muscle acts as a free membrane, attached at its edges to the inside of a vertical rib cage circular in cross section, that the attachments are inferior to the point at which the dome makes contract with the rib cage, and that the abdomen is filled with fluid with a hydrostatic gradient in pressure. The shape is different from a section of a sphere, with a radius of curvature substantially greater at the apex of the dome than at the sides. Observed shapes of human hemidiaphragm domes at functional residual capacity are not spherical but closely match the calculated shapes. Best-fitting shapes correspond to transdiaphragmatic pressures of about 3 cmH2O transdiaphragmatic pressure, suggesting that such a pressure and corresponding tension are present in the human diaphragm when it is at rest in an erect subject. In this model; as lung volume increases and the diaphragm shortens, its shape changes in such a way that the ratio between transdiaphragmatic pressure and tension in the diaphragm remains nearly constant, rather than increasing with volume. Such a model can explain the observation that the length-tension relationship of the muscle is much more important than curvature in determining the effectiveness of the diaphragm as a pressure generator.     

Metabolic consequences of positive inotropy in rat and guinea-pig hearts

The metabolic and physiological responses of hearts from male rats and guinea-pigs to isoprenaline and SK&F 94120 (a phosphodiesterase III inhibitor), have been studied. Doses which gave similar chronotropic stimulation gave different inotropic responses. In both species, isoprenaline generated a greater increase in developed tension than SK&F 94120. With both drugs the inotropic response in the rat was less than than in the guinea-pig. 31P-NMR investigation of high-energy phosphate levels showed reduction in PCr concentration and an accompanying acidosis in the isoprenaline-perfused rat heart only. In both species, lactate production was stimulated by SK&F 94120 but not by isoprenaline. These results are discussed with reference to G-protein activation of ion channels and differences in Ca2+ handling by the two species.     

Relationships between regional myocardial wall stress and bioenergetics in hearts with left ventricular hypertrophy

This study utilized porcine models of postinfarction left ventricular (LV) remodeling [myocardial infarction (MI); n = 8] and concentric LV hypertrophy secondary to aortic banding (AoB; n = 8) to examine the relationships between regional myocardial contractile function (tagged MRI), wall stress (MRI and LV pressure), and bioenergetics ((31)P-magnetic resonance spectroscopy). Physiological assessments were conducted at a 4-wk time point after MI or AoB surgery. Comparisons were made with size-matched normal animals (normal; n = 8). Both MI and AoB instigated significant LV hypertrophy. Ejection fraction was not significantly altered in the AoB group, but significantly decreased in the MI group (P < 0.01 vs. normal and AoB). Systolic and diastolic wall stresses were approximately two times greater than normal in the infarct region and border zone. Wall stress in the AoB group was not significantly different from that in normal hearts. The infarct border zone demonstrated profound bioenergetic abnormalities, especially in the subendocardium, where the ratio of PCr/ATP decreased from 1.98 +/- 0.16 (normal) to 1.06 +/- 0.30 (MI; P < 0.01). The systolic radial thickening fraction and the circumferential shortening fraction in the anterior wall were severely reduced (MI, P < 0.01 vs. normal). The radial thickening fraction and circumferential shortening fraction in the AoB group were not significantly different from normal. The severely elevated wall stress in the infarct border zone was associated with a significant increase in chemical energy demand and abnormal myocardial energy metabolism. Such severe metabolic perturbations cannot support normal cardiac function, which may explain the observed regional contractile abnormalities in the infarct border zone.     

Prostaglandin E2 and cyclic AMP in the coronary vasodilatation due to cardiac hyperactivity.

In the isolated perfused rat heart, the dose-related cardiostimulation produced by norepinephrine (NE) or calcium chloride (Ca2+) was followed by a corresponding increase in coronary flow (CF) and in the cardiac level of adenosine 3',5'-cyclic phosphate (cAMP). Prolonged prostaglandin E2 (pge2) infusion did not change the basic force of contraction, CF, or cAMP level but when NE or Ca2+ were administered, only the responses of the CF and the cAMP were diminished. A phosphodiesterase inhibitor, diazoxide (Dx), caused insignificant increase in the basal cAMP, without affecting the force of contraction or CF. With NE or Ca2+, during Dx both the changes in CF and cAMP were augmented compared to the nontreated hearts. The inhibitory effects of NE or Ca2+ remained unchanged. Propranolol abolished the NE but not the Ca2+ effects. It is suggested that PGE2 modulates the cardiac cAMP level and that the latter plays an important role in the adaptive regulation of the CF. It is also postulated that changes in cAMP levels may be brought about by the hyperactivity per se produced by a variety of cardiostimulating agents.     

Relationships between pulmonary inflammation, plasma transudation, and oxygen metabolite secretion by alveolar macrophages

We have previously shown that alveolar macrophages from normal rabbit lungs do not synthesize reactive oxygen intermediates unless first conditioned by culture in vitro in the presence of serum for 24 to 48 hr. This conditioning process is mediated by a serum constituent that partitions on gel exclusion columns with an apparent m.w. of 30,000 to 50,000 daltons. Alveolar macrophage conditioning in vitro requires protein synthesis, is associated with the generation of membrane NADPH oxidase activity, and is reversible. We have predicted therefore that during the course of pulmonary inflammation, as observed 3 wk after i.v. injection of M. butyricum in oil, alveolar macrophages might similarly become conditioned in vivo through exposure to plasma protein transudates reaching the alveolus. In support of this hypothesis we show that after experimental production of granulomatous pulmonary inflammation in rabbits, alveolar macrophages showed an augmented capacity to secrete superoxide anion when stimulated with phorbol ester, and this enhancement increases exponentially with increased plasma transudation. This augmented enhancement was reversible, and decreased after culture in vitro in the absence of serum. Mature alveolar macrophages were responsible for this enhanced superoxide anion production rather than freshly emigrated monocytes. Moreover, superoxide anion production in this model of pulmonary inflammation appears to be an "all-or-none" phenomenon, with superoxide anion production associated with a subpopulation of optimally conditioned alveolar macrophages, whereas the remaining unconditioned alveolar macrophages produce little or none. We feel that these two classes of alveolar macrophages may be derived from inflamed and noninflamed regions of the lung, respectively, thereby reflecting the discontinuous nature of the inflammatory lesions themselves. Thus we propose that measurements of reactive oxygen intermediate production by lavaged alveolar macrophages may provide a semi-quantitative measure of chronic pulmonary inflammation.     

Swimming performance, venous oxygen tension and cardiac performance of coronary-ligated rainbow trout, Oncorhynchus mykiss, exposed to progressive hypoxia

We performed in vivo studies to examine the idea that cardiac work is impaired in rainbow trout (Oncorhynchus mykiss) below a certain venous PO2 threshold. We hypothesized that coronary-ligated fish, swimming continuously at a reasonably high water velocity (1.5 body lengths x s(-1)) and exposed to progressive hypoxia, would fatigue at higher venous PO2 and ambient water PO2 compared with sham-operated fish. However, we found that both the lowest venous PO2 that supported hypoxic swimming (9.9 torr for coronary-ligated fish and 11.1 torr for sham-operated fish) and the venous PO2 at fatigue (7.8 torr and 8.6 torr, respectively) were the same for coronary-ligated and sham-operated fish. Also, both groups quit swimming at the same water PO2 heart rate and hematocrit. Nevertheless, significant differences in cardiac performance did exist between the two groups. Whereas ventral aortic blood pressure (Pva) increased significantly with hypoxic swimming in sham-operated fish, there was no such increase in coronary-ligated fish. In addition, cardiac arrhythmias occurred in coronary-ligated fish at fatigue, and these fish were slower to recover from exhaustion. We believe that the venous PO2 threshold to support cardiac performance in the absence of a coronary supply was between 7.8 and 9.9 torr. Furthermore, we suspect that the low PO2 in coronary-ligated fish effectively lowered their myocardial O2 demand. Uncertainty still exists regarding whether or not the venous PO2 threshold lies between 8.6 and 11.1 torr in sham-operated fish.     

Calcium antagonists, ventricular fibrillation, and enzyme release in ischemic rat hearts

Early experiments with the calcium antagonist verapamil showed that it could inhibit the transsarcolemmal influx of calcium ions induced by isoproterenol in ventricular myocardium without inhibiting the effect of beta stimulation to increase tissue cyclic AMP. Current views of the effects of the beta-receptor-adenylate cyclase-cyclic AMP system of the calcium channel suggest that both calcium antagonists and beta-adrenoceptor antagonists should inhibit transsarcolemmal calcium influx if calcium is the third messenger of beta-agonist catecholamines. When high concentrations of circulating catecholamines are added to normal isolated hearts, two of the effects include increased vulnerability to ventricular fibrillation and high rates of enzyme release. These effects are antagonized by beta-adrenoceptor inhibitors and by calcium antagonists, which suggests a classical second (cyclic AMP) and third (calcium) messenger effect. In the presence of coronary artery ligation, the ventricular fibrillation threshold falls and enzyme release is enhanced. Both effects are associated with an increased tissue cyclic AMP level in the ischemic zone and are susceptible to calcium antagonist procedures. Neither effect can be fully stopped by beta-adrenoceptor antagonism. Therefore the evidence from this model with coronary artery ligation favors the views that 1) cyclic AMP accumulates in ischemic tissue by a process not fully susceptible to inhibition by beta-adrenoceptor antagonists; and 2) calcium ions are associated with the development of ventricular fibrillation and enzyme release by a process susceptible to inhibition by calcium antagonist agents such as verapamil, nifedipine, and diltiazem.     

Relationship between coronary flow and adenosine release in reactive hyperemia

A linear relationship was found between coronary flow and adenosine release during the course of reactive hyperemia. Isolated guinea pig heart was perfused with a modified Krebs Ringer bicarbonate buffer containing 2.0 mM pyruvate. Hyperemia was induced with 30, 60 and 90-second coronary occlusions. The hyperemic response was divided into three consecutive 13-second intervals (I, II and III), and perfusate efflux from coronary circulation was collected during the last 10 seconds of each interval for adenosine assay using the HPLC. The data show a control flow of 3.13 +/- 0.4 ml/min/g and adenosine release of 66 +/- 4 pmoles/min/g. Flow increased by 99, 38 and 23% at I, II and III, respectively following 30-second occlusion, whereas adenosine release increased by 241, 132 and 91% for I, II and III. A 60-second occlusion increased the flow by 125, 64 and 34% with a simultaneous increase in the release of adenosine by 464, 155 and 133%, respectively, for I, II and III. Marked elevations in flow (165, 92 and 59%) and in adenosine release (659, 194 and 176%) for I, II and III were observed following 90-second occlusion. The linear relationship between coronary flow and adenosine release had r values of 0.84, 0.74 and 0.88 for 30, 60 and 90-second occlusions, respectively. This study quantifies the relationship between coronary flow and adenosine release during the course of reactive hyperemia. It also suggests that on a percent basis, adenosine contributes equally to the hyperemia at I, II and III.     

Interaction between L-arginine: no system and cyclooxygenase metabolic products of arachidonic acid in coronary autoregulation.

Coronary autoregulation (CA) is the intrinsic ability of the heart to maintain its nutritive blood supply constant over a wide range of perfusion pressure. This phenomenon is regulated through several control mechanisms, while metabolic and myogenic control mechanism have dominant effects. In last few years, endothelial control mechanism, which is part of metabolic control, was intensive investigated. Dominant topic of endothelial-investigation was bioregulatory L-arginine: NO system, with his effective product--nitric oxide (NO). On the other hand, cyclooxygenase metabolic pathway products of arachidonic acid plays an important role in the control of vasomotor tone of coronary arteries. For this purpose, the aim of our study was to evaluate role of L-arginine: NO system, cyclooxygenase metabolites of arachidonic acid, as well as, their interactions in the control of CA of the isolated rat heart.. In our study rat hearts autoregulate CF between 50 and 90 cm H2O of CPP. Basal release (at 60 cm H2O) of NO (as nitrite), cAMP, cGMP and HX+X (i.e. adenosine) amounted to 2.85+/-0.25 nmol/min/g wt, 29.45+/-2.22 pmol/min/g wt, 0.43+/-0.08 pmol/min/g wt and 37.50+/-2.89 nmol/min/g wt respectively. Release of NO, cAMP and cGMP were strictly parallel with CPP-CF curve, while release of adenosine (i.e. HX + X) was an inverse function of perfusion pressure. Inhibition of NOS (L-NAME, 30 micromol/l) significantly widened autoregulatory range (40-100 cm H2O), with significant reduction in CF and NO- and cGMP release, while release of cAMP was completely reversed in the presence of L-NAME. However, inhibition of cyclooxygenase didn't influence autoregulatory range, with similar changes of NO- and cAMP-release and completely inversed values of released adenosine. When L-NAME an indomethacin (an nonspecific COX-inhibitor), 3 micromol/l where added together, they exhibit interactions between these two enzymatic systems. Namely, when L-NAME was added first, indomethacin didn't influence hemodynamic effects of NOS-inhibitor. On the other hand, when COX-inhibitor was added first, L-NAME widened autoregulatory range in small manner as after control autoregulatory experiments (40-90 cm H2O). All hemodynamic changes were followed with similar changes in NO-release, what suggest that exist interaction between L-arginine: NO system and COX-metabolites in the regulation of coronary autoregulation.