Alveolar liquid clearance in multiple nonperfused canine lung lobes

Grimme, John D., Susan M. Lane, and Michael B. Maron.Alveolar liquid clearance in multiple nonperfused canine lung lobes. J. Appl. Physiol. 82(1):348-353, 1997.We evaluated the ability of canine isolatednonperfused lung lobes to absorb fluid from their air spaces bysimultaneously measuring alveolar liquid clearance (ALC) in three lobesremoved from the same dog. Autologous plasma was instilled in the airspaces of each lobe, and the increase in plasma protein concentrationresulting from fluid reabsorption was used to calculate ALC. ALC after4 h was 16.5 ± 0.6% (SE) of the instilled fluid volume underbaseline conditions and was 30.2 ± 1.3% after terbutaline(10⁵ M) administration.These values were similar to those previously reported for intact dogs.Propranolol (10⁴ M) andouabain (10³ M) reduced ALCin terbutaline-stimulated lobes to 20.4 ± 0.8 and 3.9 ± 1.4%,respectively. There was no significant difference in ALC among thethree lobes under either baseline conditions or after terbutalineadministration. These data indicate that the sodium and water transportmechanisms of the canine alveolar epithelium remain viable during 4 hof nonperfusion and that there are no intrinsic differences in thetransport properties of individual lung lobes. The ability to studyseveral lobes simultaneously without the need for perfusion will allowfor the design of experiments in which multiple interventions can bestudied by using lung lobes from the same animal.

     

Alveolar epithelial fluid clearance persists in the presence of moderate left atrial hypertension in sheep

The effect of moderate left atrial(LA) hypertension on alveolar liquid clearance (ALC) wasinvestigated in anesthetized, ventilated sheep, surgically prepared tomeasure lung lymph flow as well as hemodynamics. To simulate alveolaredema, 3-4 ml/kg of isosmolar 5% albumin in Ringer lactate wereinstilled into each lower lobe, and ALC was measured. After 4 h of LAhypertension (24 cmH₂O), ALC wassimilar to that in control sheep (31 ± 3% with LA hypertension vs.34 ± 10% with normal LA pressure). Because plasma epinephrinelevels were moderately elevated in the presence of LA hypertension, ALCwas then studied in the presence of LA hypertension following bilateraladrenalectomy. Without endogenous release of epinephrine, ALC wassignificantly reduced compared with normal LA pressure (20 ± 7%compared with 34 ± 10%, P < 0.05). Thus endogenous catecholamines caused a submaximal stimulation of ALC in the presence of LA hypertension. Exogenous administration ofaerosolized ₂-agonist therapywith salmeterol increased ALC in the presence of normal LA pressure buthad no stimulatory effect in the presence of moderate LA hypertension.Therefore, we tested the hypothesis that endogenous release of atrialnatriuretic factor (ANF) may downregulate alveolar epithelialNa⁺ and fluid transport in thepresence of LA hypertension. There was a modest twofold increase inplasma ANF levels after LA hypertension. Additional in vitro studiesdemonstrated that, in the presence of₂-agonist stimulation, ANFdecreased Na⁺ pump activity(Na⁺-K⁺-ATPase)in isolated rat alveolar epithelial type II cells. ANF may downregulatevectorial Na⁺ and fluid transportstimulated by endogenous or exogenous -adrenergic agoniststimulation in the presence of LA hypertension. In summary, ALCcontinues even in the presence of moderate LA hypertension. Aerosolized₂-adrenergic agonist therapysignificantly increased ALC, but only when LA pressure was normal.

     

Fluid and electrolyte hormonal responses to exercise and acute plasma volume expansion

Grant, S. M., H. J. Green, S. M. Phillips, D. L. Enns, andJ. R. Sutton. Fluid and electrolyte hormonal responses to exerciseand acute plasma volume expansion. J. Appl.Physiol. 81(6): 2386-2392, 1996.To investigatethe effect of acute graded increases in plasma volume (PV) on fluid andregulatory hormone levels, eight untrained men (peak aerobic power 45.2 ± 2.2 ml ^· kg^{1 ·} min¹)performed prolonged cycle exercise (46 ± 4% maximal aerobic poweron three occasions, namely, with no PV expansion (Con) and after 14%(Low) and 21% (High) expansions, respectively. The exercise plasmalevels of aldosterone (Aldo), arginine vasopressin (AVP), and atrialnatriuretic peptide (ANP) were all altered by acute PV increases. Apronounced blunting (P < 0.05) ofthe Aldo response during exercise was observed, the magnitude of whichwas directly related to the amount of hypervolemia (Con < Low < High). At 120 min of exercise, Aldo concentrations were 660 ± 71, 490 ± 85, and 365 ± 78 pg/ml for Con, Low, and High conditions,respectively. In contrast, the lower AVP and the higher ANP observedduring exercise appeared to be due to the effect of PV expansion onresting concentrations. Because osmolality did not vary amongconditions, the results indicate that PV represents an importantprimary stimulus in the response of Aldo to exercise. The lowerexercise blood concentrations of both epinephrine and norepinephrineobserved with PV expansion would suggest that a lower sympathetic drive may be implicated at least in the lower Aldo responses.

     

Fuel metabolism in men and women during and after long-duration exercise

This study aimed to determine gender-baseddifferences in fuel metabolism in response to long-duration exercise.Fuel oxidation and the metabolic response to exercise were compared inmen (n = 14) and women(n = 13) during 2 h (40% of maximalO₂ uptake) of cycling and 2 h ofpostexercise recovery. In addition, subjects completed a separatecontrol day on which no exercise was performed. Fuel oxidation wasmeasured using indirect calorimetry, and blood samples were drawn forthe determination of circulating substrate and hormone levels. Duringexercise, women derived proportionally more of the total energyexpended from fat oxidation (50.9 ± 1.8 and 43.7 ± 2.1% forwomen and men, respectively, P < 0.02), whereas men derived proportionally more energy from carbohydrateoxidation (53.1 ± 2.1 and 45.7 ± 1.8% for men and women,respectively, P < 0.01). Thesegender-based differences were not observed before exercise, afterexercise, or on the control day. Epinephrine(P < 0.007) and norepinephrine(P < 0.0009) levels weresignificantly greater during exercise in men than in women (peakepinephrine concentrations: 208 ± 36 and 121 ± 15 pg/ml in menand women, respectively; peak norepinephrine concentrations: 924 ± 125 and 659 ± 68 pg/ml in men and women, respectively). Ascirculating glycerol levels were not different between the two groups,this suggests that women may be more sensitive to the lipolytic action of the catecholamines. In conclusion, these data support the view thatdifferent priorities are placed on lipid and carbohydrate oxidationduring exercise in men and women and that these gender-based differences extend to the catecholamine response to exercise.

     

Regional measurements of pulmonary edema by using magnetic resonance imaging

Athree-dimensional magnetic resonance imaging (MRI) method to measurepulmonary edema and lung microvascular barrier permeability wasdeveloped and compared with conventional methods in nine mongrel dogs.MRIs were obtained covering the entire lungs. Injury was induced byinjection of oleic acid (0.021-0.048 ml/kg) into a jugularcatheter. Imaging followed for 0.75-2 h. Extravascular lung waterand permeability-related parameters were measured from multiple-indicator dilution curves. Edema was measured as magnetic resonance signal-to-noise ratio (SNR). Postinjury wet-to-dry lung weight ratio was 5.30 ± 0.38 (n = 9). Extravascular lung water increased from 2.03 ± 1.11 to 3.00 ± 1.45 ml/g(n = 9, P < 0.01). Indicatordilution studies yielded parameters characterizing capillary exchangeof urea and butanediol: the product of the square root of equivalentdiffusivity of escape from the capillary and capillary surface area(D^1/2S)and the capillary permeability-surface area product(PS). The ratio ofD^1/2Sfor urea toD^1/2Sfor butanediol increased from 0.583 ± 0.027 to 0.852 ± 0.154 (n = 9, P < 0.05). Whole lung SNR atbaseline, before injury, correlated withD^1/2Sand PS ratios (both P < 0.02). By using rate of SNR change, the mismatch of transcapillaryfiltration flow and lymph clearance was estimated to be0.2-1.8 ml/min. The filtration coefficient was estimated fromthese values. Results indicate that pulmonary edema formation duringoleic acid injury can be imaged regionally and quantified globally, andthe results suggest possible regional quantification by usingthree-dimensional MRI.

     

Effects of the ovarian cycle on sympathetic neural outflow during static exercise

We comparedreflex responses to static handgrip at 30% maximal voluntarycontraction (MVC) in 10 women (mean age 24.1 ± 1.7 yr) during twophases of their ovarian cycle: the menstrual phase (days 1-4) and the follicularphase (days10-12). Changes in muscle sympathetic nerve activity (MSNA; microneurography) in response tostatic exercise were greater during the menstrual compared withfollicular phase (phase effect P = 0.01). Levels of estrogen were less during the menstrual phase(75 ± 5.5 vs. 116 ± 9.6 pg/ml, days 1-4 vs.days 10-12;P = 0.002). Generated tension did not explain differences in MSNA responses (MVC: 29.3 ± 1.3 vs. 28.2 ± 1.5 kg, days 1-4 vs.days 10-12;P = 0.13). In a group of experiments with the use of ³¹P-NMRspectroscopy, no phase effect was observed forH⁺ andH₂PO₄ concentrations(n = 5). During an ischemicrhythmic handgrip paradigm (20% MVC), a phase effect was notobserved for MSNA or H⁺ orH₂PO₄ concentrations,suggesting that blood flow was necessary for the expression of thecycle-related effect. The present studies suggest that, during statichandgrip exercise, MSNA is increased during the menstrual compared withthe follicular phase of the ovarian cycle.

     

Effect of epinephrine on muscle glycogenolysis during exercise in trained men

Febbraio, M. A., D. L. Lambert, R. L. Starkie, J. Proietto,and M. Hargreaves. Effect of epinephrine on muscle glycogenolysis during exercise in trained men. J. Appl.Physiol. 84(2): 465-470, 1998.To test thehypothesis that an elevation in circulating epinephrine increasesintramuscular glycogen utilization, six endurance-trained men performedtwo 40-min cycling trials at 71 ± 2% of peak oxygen uptake in20-22°C conditions. On the first occasion, subjects wereinfused with saline throughout exercise (Con). One week later, afterdetermination of plasma epinephrine levels in Con, subjects performedthe second trial (Epi) with an epinephrine infusion, which resulted ina twofold higher (P < 0.01) plasmaepinephrine concentration in Epi compared with Con. Although oxygenuptake was not different when the two trials were compared, respiratoryexchange ratio was higher throughout exercise in Epi compared with Con(0.93 ± 0.01 vs. 0.89 ± 0.01; P < 0.05). Muscle glycogenconcentration was not different when the trials were comparedpreexercise, but the postexercise value was lower(P < 0.01) in Epi compared with Con.Thus net muscle glycogen utilization was greater during exercise withepinephrine infusion (224 ± 37 vs. 303 ± 30 mmol/kg for Con andEpi, respectively; P < 0.01). Inaddition, both muscle and plasma lactate and plasma glucoseconcentrations were higher (P < 0.05) in Epi compared with Con. These data indicate that intramuscularglycogen utilization, glycolysis, and carbohydrate oxidation areaugmented by elevated epinephrine during submaximal exercise in trainedmen.

     

Ca2+ depolarizes adrenal cortical cells through selective inhibition of an ATP-activated K+ current

Bovine adrenalzona fasciculata cells (AZF) express a noninactivatingK⁺ current(I_AC) whoseinhibition by adrenocorticotropic hormone and ANG II may be coupled tomembrane depolarization andCa²⁺-dependentcortisol secretion. We studiedI_ACinhibition byCa²⁺ and theCa²⁺ionophore ionomycin in whole cell and single-channel patch-clamp recordings of AZF. In whole cell recordings with intracellular (pipette)Ca²⁺concentration([Ca²⁺]_i)buffered to 0.02 µM,I_AC reachedmaximum current density of 25.0 ± 5.1 pA/pF(n = 16); raising[Ca²⁺]_ito 2.0 µM reduced it 76%. In inside-out patches, elevated[Ca²⁺]_idramatically reducedI_AC channelactivity. Ionomycin inhibited I_AC by 88 ± 4% (n = 14) without altering rapidlyinactivating A-type K⁺ current.Inhibition of I_ACby ionomycin was unaltered by adding calmodulin inhibitory peptide tothe pipette or replacing ATP with its nonhydrolyzable analog5'-adenylylimidodiphosphate.I_AC inhibition byionomycin was associated with membrane depolarization. When[Ca²⁺]_iwas buffered to 0.02 µM with 2 and 11 mM1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), ionomycin inhibitedI_AC by 89.6 ± 3.5 and 25.6 ± 14.6% and depolarized the same AZF by 47 ± 8 and 8 ± 3 mV, respectively (n = 4). ANG II inhibitedI_AC significantlymore effectively when pipette BAPTA was reduced from 11 to 2 mM. Raising[Ca²⁺]_iinhibits I_ACthrough a mechanism not requiring calmodulin or protein kinases,suggesting direct interaction withI_AC channels. ANGII may inhibitI_AC anddepolarize AZF by activating parallel signaling pathways, one of whichuses Ca²⁺ asa mediator.

     

K+ supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+ homeostasis in rats

Bundgaard, Henning, Thomas A. Schmidt, Jim S. Larsen, andKeld Kjeldsen. K⁺supplementation increases muscle[Na⁺-K⁺-ATPase]and improves extrarenal K⁺homeostasis in rats. J. Appl. Physiol.82(4): 1136-1144, 1997.Effects ofK⁺ supplementation (~200 mmolKCl/100 g chow) on plasma K⁺,K⁺ content, andNa⁺-K⁺-adeonsinetriphosphatase(ATPase) concentration([Na⁺-K⁺-ATPase])in skeletal muscles as well as on extrarenalK⁺ clearance were evaluated inrats. After 2 days of K⁺supplementation, hyperkalemia prevailed(K⁺-supplemented vs.weight-matched control animals) [5.1 ± 0.2 (SE) vs. 3.2 ± 0.1 mmol/l, P < 0.05, n = 5-6], and after 4 daysa significant increase in K⁺content was observed in gastrocnemius muscle (104 ± 2 vs. 97 ± 1 µmol/g wet wt, P < 0.05, n = 5-6). After 7 days ofK⁺ supplementation, a significantincrease in[³H]ouabain bindingsite concentration (344 ± 5 vs. 239 ± 8 pmol/g wet wt,P < 0.05, n = 4) was observed in gastrocnemiusmuscle. After 2 wk, increases in plasmaK⁺,K⁺ content, and[³H]ouabain bindingsite concentration in gastrocnemius muscle amounted to 40, 8, and 68%(P < 0.05) above values observed inweight-matched control animals, respectively. The latter change wasconfirmed by K⁺-dependentp-nitrophenyl phosphatase activitymeasurements. Fasting for 1 day reduced plasmaK⁺ andK⁺ content in gastrocnemius musclein rats that had been K⁺supplemented for 2 wk by 3.1 ± 0.3 mmol/l(P < 0.05, n = 5) and 15 ± 2 µmol/g wet wt(P < 0.05, n = 5), respectively. After induction of anesthesia, arterial plasma K⁺was measured during intravenous KCl infusion (0.75 mmolKCl · 100 g bodywt¹ · h¹).The K⁺-supplemented fasted groupdemonstrated a 42% (P < 0.05) lower plasma K⁺ rise, associated with asignificantly higher increase inK⁺ content in gastrocnemius muscleof 7 µmol/g wet wt (P < 0.05, n = 5) compared with their controlanimals. In conclusion, K⁺supplementation increases plasmaK⁺,K⁺ content, and[Na⁺-K⁺-ATPase]in skeletal muscles and improves extrarenalK⁺ clearance capacity.

     

LY-294002-inhibitable PI 3-kinase and regulation of baseline rates of Na(+) transport in A6 epithelia

Blocker-inducednoise analysis of epithelial Na⁺ channels (ENaCs) was usedto investigate how inhibition of an LY-294002-sensitive phosphatidylinositol 3-kinase (PI 3-kinase) alters Na⁺transport in unstimulated and aldosterone-prestimulated A6 epithelia. From baseline Na⁺ transport rates(I_Na) of 4.0 ± 0.1 (unstimulated) and9.1 ± 0.9 µA/cm² (aldosterone), 10 µM LY-294002caused, following a relatively small initial increase of transport, acompletely reversible inhibition of transport within 90 min to 33 ± 6% and 38 ± 2% of respective baseline values. Initialincreases of transport could be attributed to increases of channel openprobability (P_o) within 5 min to 143 ± 17% (unstimulated) and 142 ± 10% of control (aldosterone) frombaseline P_o averaging near 0.5. Inhibition oftransport was due to much slower decreases of functional channeldensities (N_T) to 28 ± 4% (unstimulated)and 35 ± 3% (aldosterone) of control at 90 min. LY-294002 (50 µM) caused larger but completely reversible increases ofP_o (215 ± 38% of control at 5 min) andmore rapid but only slightly larger decreases ofN_T. Basolateral exposure to LY-294002 induced nodetectable effect on transport, P_o or N_T. We conclude that an LY-294002-sensitive PI3-kinase plays an important role in regulation of transport bymodulating N_T and P_o ofENaCs, but only when presented to apical surfaces of the cells.

     

Effects of edema on small airway narrowing

Wagner, Elizabeth M. Effects of edema on small airwaynarrowing. J. Appl. Physiol. 83(3):784-791, 1997.Numerous mediators of inflammation have beendemonstrated to cause airway microvascular fluid and proteinextravasation. That fluid extravasation results in airway wall edemaleading to airway narrowing and enhanced reactivity has not beenconfirmed. In anesthetized, ventilated sheep(n = 30), airway vascularfluid extravasation was induced by infusing bradykinin(10⁶ M) through acannulated, blood-perfused bronchial artery. Airway wall edema andluminal narrowing were determined morphometrically. Airway reactivityto methacholine (MCh; 10 µg/ml, intrabronchial artery) was determinedby measuring conducting airway resistance (Raw) by forced oscillation.Raw measurements were made and lung lobes were excised and quick frozenbefore or after a 1-h bradykinin infusion. In 10 airways per lobe(range 0.2- to 2.0-mm relaxed diameter), wall area occupied 32 ± 2% (SE) of the total normalized airway area(n = 9). Bradykinin infusion increasedwall area to 42 ± 5% (P = 0.02);luminal area decreased by <5%; and smooth muscle perimeter, ameasure of smooth muscle constriction, was not altered(n = 5). Raw showed nochange from baseline (1.4 ± 0.4 cmH₂O · l¹ · s)after bradykinin infusion (n = 10).During MCh challenge, Raw increased by 3.2 ± 04 cmH₂O · l¹ · s,and this change did not differ after administration of bradykinin. MChchallenge caused similar decreases in smooth muscle perimeter (10%)and luminal area (72 vs. 68%) before and after bradykinin infusion.However, the time constant of recovery of Raw from MCh constriction wasincreased from control (40 ± 3 s) to 57 ± 10 s after bradykinininfusion (P = 0.03). When lung lobeswere excised at the same time after MCh challenge was terminated(n = 5), luminal area was greaterbefore bradykinin infusion than after (86 vs. 78%;P = 0.007), as was smooth muscleperimeter. The results of this study demonstrate that airway wall edemalimits relaxation after induced constriction rather than enhancingconstriction.

     

A3 adenosine receptors regulate Cl- channels of nonpigmented ciliary epithelial cells

Adenosinestimulates Cl channels ofthe nonpigmented (NPE) cells of the ciliary epithelium. We sought toidentify the specific adenosine receptors mediating this action.Cl channel activity inimmortalized human (HCE) NPE cells was determined by monitoring cellvolume in isotonic suspensions with the cationic ionophore gramicidinpresent. The A₃-selective agonistN⁶-(3-iodobenzyl)-adenosine-5'-N-methyluronamide(IB-MECA) triggered shrinkage (apparentK_d = 55 ± 10 nM). A₃-selective antagonists blocked IB-MECA-triggered shrinkage, andA₃-antagonists (MRS-1097, MRS-1191, and MRS-1523) also abolished shrinkage produced by 10 µMadenosine when all four known receptor subtypes are occupied. TheA₁-selective agonistN⁶-cyclopentyladenosineexerted a small effect at 100 nM but not at higher or lowerconcentrations. The A_2A agonistCGS-21680 triggered shrinkage only at high concentration (3 µM), aneffect blocked by MRS-1191. IB-MECA increased intracellularCa²⁺ in HCE cells and alsostimulated short-circuit current across rabbit ciliary epithelium.A₃ message was detected in bothHCE cells and rabbit ciliary processes using RT-PCR. We conclude that human HCE cells and rabbit ciliary processes possessA₃ receptors and that adenosinecan activate Cl channels inNPE cells by stimulating these A₃ receptors.     

Na+-K+-ATPase in frog esophagus mucociliary cell membranes: inhibition by protein kinase C activation

We examined protein kinase C (PKC)-dependentregulation ofNa⁺-K⁺-ATPasein frog mucociliary cells. Activation of PKC by12-O-tetradecanoylphorbol-13-acetate (TPA) or 1,2-dioctanoyl-sn-glycerol(diC8) either in intact cells or isolated membranes resulted in aspecific inhibition ofNa⁺-K⁺-ATPaseactivity by ~25-45%. The inhibitory effects in membranes exhibited time dependence and dose dependence [half-maximalinhibition concentration (IC₅₀) = 0.5 ± 0.1 nM and 2.4 ± 0.2 µM, respectively, for TPA anddiC8] and were not influenced byCa²⁺. Analysis of the ouabaininhibition pattern revealed the presence of twoNa⁺-K⁺-ATPaseisoforms with IC₅₀ values forcardiac glycoside of 2.6 ± 0.8 nM and 409 ± 65 nM,respectively. Most importantly, the isoform possessing a higheraffinity for ouabain was almost completely inhibited by TPA, whereasits counterpart was hardly sensitive to the PKC activator. The resultssuggest that, in frog mucociliary cells, PKC regulatesNa⁺-K⁺-ATPaseand that this action is related to the specificNa⁺-K⁺-ATPaseisoform.

     

Esophageal temperature threshold for sweating decreases before ovulation in premenopausal women

The purpose ofthis study was to test the hypothesis that regulated body temperatureis decreased in the preovulatory phase in eumenorrheic women. Six womenwere studied in both the preovulatory phase (Preov-2;days 9-12), which was 1-2days before predicted ovulation when 17-estradiol(E₂) was estimated to peak, andin the follicular phase (F; days2-6). The subjects walked on a treadmill (~225W · m²)in a warm chamber (ambient temperature = 30°C; dew-pointtemperature = 11.5°C) while heavily clothed.E₂, esophageal temperature(T_es), local skin temperatures,and local sweating rate were measured. The estimate of when theE₂ surge would occur was correctfor four of six subjects. In these four subjects,E₂ increased(P  0.05) from 42.0 ± 24.5 pg/mlduring F to 123.2 ± 31.3 pg/ml during Preov-2. RestingT_es was 37.02 ± 0.20°Cduring F and 36.76 ± 0.28°C during Preov-2(P  0.05). TheT_es threshold for sweating wasdecreased (P  0.05) from 36.88 ± 0.27°C during F to 36.64 ± 0.35°C during Preov-2. Both meanskin and mean body temperatures were decreased during rest in Preov-2group. The hypothesis that regulated body temperature is decreasedduring the preovulatory phase is supported.

     

Optical measurement of isolated canine lung filtration coefficients at normal hematocrits

Klaesner, Joseph W., N. Adrienne Pou, Richard E. Parker,Charlene Finney, and Robert J. Roselli. Optical measurement ofisolated canine lung filtration coefficients at normal hematocrits. J. Appl. Physiol. 83(6):1976-1985, 1997.In this study, lung filtration coefficient(K_fc) valueswere measured in eight isolated canine lung preparations at normalhematocrit values using three methods: gravimetric, blood-correctedgravimetric, and optical. The lungs were kept in zone 3 conditions andsubjected to an average venous pressure increase of 10.24 ± 0.27 (SE) cmH₂O. The resulting K_fc(ml · min¹ · cmH₂O¹ · 100 g dry lung wt¹) measuredwith the gravimetric technique was 0.420 ± 0.017, which wasstatistically different from theK_fc measured bythe blood-corrected gravimetric method (0.273 ± 0.018) or theproduct of the reflection coefficient(_f) andK_fc measuredoptically (0.272 ± 0.018). The optical method involved the use of aCellco filter cartridge to separate red blood cells from plasma, whichallowed measurement of the concentration of the tracer in plasma atnormal hematocrits (34 ± 1.5). The permeability-surface areaproduct was measured using radioactive multiple indicator-dilutionmethods before, during, and after venous pressure elevations. Resultsshowed that the surface area of the lung did not change significantlyduring the measurement ofK_fc. Thesestudies suggest that_fK_fccan be measured optically at normal hematocrits, that this measurement is not influenced by blood volume changes that occur during the measurement, and that the optical_fK_fcagrees with theK_fc obtained viathe blood-corrected gravimetric method.

     

Role of inhibition of nitric oxide production in monocrotaline-induced pulmonary hypertension

Mathew, Rajamma, Elizabeth S. Gloster, T. Sundararajan, Carl I. Thompson, Guillermo A. Zeballos, andMichael H. Gewitz. Role of inhibition of nitric oxide productionin monocrotaline-induced pulmonary hypertension. J. Appl. Physiol. 82(5): 1493-1498, 1997.Monocrotaline (MCT)-induced pulmonary hypertension (PH) isassociated with impaired endothelium-dependent nitric oxide(NO)-mediated relaxation. To examine the role of NO in PH,Sprague-Dawley rats were given a single subcutaneous injection ofnormal saline [control (C)], 80 mg/kg MCT, or the same doseof MCT and a continuous subcutaneous infusion of 2 mg · kg¹ · day¹of molsidomine, a NO prodrug (MCT+MD). Two weeks later, plasma NO₃ levels, pulmonary arterialpressure (Ppa), ratio of right-to-left ventricular weights (RV/LV) toassess right ventricular hypertrophy, and pulmonary histology wereevaluated. The plasma NO₃ level inthe MCT group was reduced to 9.2 ± 1.5 µM(n = 12) vs. C level of 17.7 ± 1.8 µM (n = 8; P < 0.02). In the MCT+MD group,plasma NO₃ level was 12.3 ± 2.0 µM (n = 8). Ppa and RV/LV in theMCT group were increased compared with C [Ppa, 34 ± 3.4 mmHg(n = 6) vs. 19 ± 0.8 mmHg(n = 8) and 0.41 ± 0.01 (n = 9) vs. 0.25 ± 0.008 (n = 8), respectively;P < 0.001]. In the MCT+MDgroup, Ppa and RV/LV were not different when compared with C [19 ± 0.5 mmHg (n = 5) and 0.27 ± 0.01 (n = 9), respectively;P < 0.001 vs. MCT]. Medial wall thickness of lung vessels in the MCT group was increased comparedwith C [31 ± 1.5% (n = 9)vs. 13 ± 0.66% (n = 9);P < 0.001], and MDpartially prevented MCT-induced pulmonary vascular remodeling [22 ± 1.2% (n = 11);P < 0.001 vs. MCT and C].These results indicate that a defect in the availability of bioactive NO may play an important role in the pathogenesis of MCT-induced PH.

     

Structure, function, and genomic organization of human Na(+)-dependent high-affinity dicarboxylate transporter

We have clonedand functionally characterized the human Na⁺-dependenthigh-affinity dicarboxylate transporter (hNaDC3) from placenta. ThehNaDC3 cDNA codes for a protein of 602 amino acids with 12 transmembrane domains. When expressed in mammalian cells, the clonedtransporter mediates the transport of succinate in the presence ofNa⁺ [concentration of substrate necessary for half-maximaltransport (K_t) for succinate = 20 ± 1 µM]. Dimethylsuccinate also interacts with hNaDC3. TheNa⁺-to-succinate stoichiometry is 3:1 and concentration ofNa⁺ necessary for half-maximal transport(K^Na+_0.5) is 49 ± 1 mM as determined by uptake studies withradiolabeled succinate. When expressed in Xenopuslaevis oocytes, hNaDC3 induces Na⁺-dependent inwardcurrents in the presence of succinate and dimethylsuccinate. At amembrane potential of 50 mV,K^Suc_0.5 is 102 ± 20 µM andK^Na+_0.5 is 22 ± 4 mM as determined by the electrophysiological approach. Simultaneous measurements of succinate-evoked charge transfer andradiolabeled succinate uptake in hNaDC3-expressing oocytes indicate acharge-to-succinate ratio of 1:1 for the transport process, suggestinga Na⁺-to-succinate stoichiometry of 3:1. pH titration ofcitrate-induced currents shows that hNaDC3 accepts preferentially thedivalent anionic form of citrate as a substrate. Li⁺inhibits succinate-induced currents in the presence of Na⁺.Functional analysis of rat-human and human-rat NaDC3 chimeric transporters indicates that the catalytic domain of the transporter lies in the carboxy-terminal half of the protein. The humanNaDC3 gene is located on chromosome20q12-13.1, as evidenced by fluorescent in situ hybridization. Thegene is >80 kbp long and consists of 13 exons and 12 introns.

     

Contribution of Na(+)-K(+)-Cl(-) cotransporter to high-[K(+)](o)- induced swelling and EAA release in astrocytes

We hypothesized that highextracellular K⁺ concentration([K⁺]_o)-mediated stimulation ofNa⁺-K⁺-Cl cotransporter isoform 1 (NKCC1) may result in a net gain of K⁺ and Cland thus lead to high-[K⁺]_o-induced swellingand glutamate release. In the current study, relative cell volumechanges were determined in astrocytes. Under 75 mM[K⁺]_o, astrocytes swelled by 20.2 ± 4.9%. This high-[K⁺]_o-mediated swelling wasabolished by the NKCC1 inhibitor bumetanide (10 µM, 1.0 ± 3.1%; P < 0.05). Intracellular³⁶Cl accumulation was increased from acontrol value of 0.39 ± 0.06 to 0.68 ± 0.05 µmol/mgprotein in response to 75 mM [K⁺]_o. Thisincrease was significantly reduced by bumetanide (P < 0.05). Basal intracellular Na⁺ concentration([Na⁺]_i) was reduced from 19.1 ± 0.8 to16.8 ± 1.9 mM by bumetanide (P < 0.05).[Na⁺]_i decreased to 8.4 ± 1.0 mM under75 mM [K⁺]_o and was further reduced to5.2 ± 1.7 mM by bumetanide. In addition, the recovery rate of[Na⁺]_i on return to 5.8 mM[K⁺]_o was decreased by 40% in the presenceof bumetanide (P < 0.05). Bumetanide inhibitedhigh-[K⁺]_o-induced ¹⁴C-labeledD-aspartate release by ~50% (P < 0.05).These results suggest that NKCC1 contributes tohigh-[K⁺]_o-induced astrocyte swelling andglutamate release.

     

Respective oxidation of 13C-labeled lactate and glucose ingested simultaneously during exercise

Péronnet, F., Y. Burelle, D. Massicotte, C. Lavoie,and C. Hillaire-Marcel. Respective oxidation of¹³C-labeled lactate and glucoseingested simultaneously during exercise. J. Appl.Physiol. 82(2): 440-446, 1997.The purpose ofthis experiment was to measure, by using¹³C labeling, the oxidation rateof exogenous lactate (25 g, as Na⁺,K⁺,Ca²⁺, andMg²⁺ salts) and glucose (75 g)ingested simultaneously (in 1,000 ml of water) during prolongedexercise (120 min, 65 ± 3% maximum oxygen uptake in 6 male subjects). The percentage of exogenous glucose and lactateoxidized were similar (48 ± 3 vs. 45 ± 5%, respectively). However, because of the small amount of oral lactate that could be tolerated without gastrointestinal discomfort, the amountof exogenous lactate oxidized was much smaller than that of exogenousglucose (11.1 ± 0.5 vs. 36.3 ± 1.3 g, respectively) andcontributed to only 2.6 ± 0.4% of the energy yield(vs. 8.4 ± 1.9% for exogenous glucose). The cumulative amount ofexogenous glucose and lactate oxidized was similar to that observedwhen 100 g of[¹³C]glucose wereingested (47.3 ± 1.8 vs. 50.9 ± 1.2 g, respectively). When[¹³C]glucose wasingested, changes in the plasma glucose¹³C/¹²Cratio indicated that between 39 and 61% of plasma glucose derived fromexogenous glucose. On the other hand, the plasma glucose ¹³C/¹²Cratio remained unchanged when[¹³C]lactate wasingested, suggesting no prior conversion into glucose before oxidation.

     

Effect of beverage osmolality on intestinal fluid absorption during exercise

To determine howosmolality of an orally ingested fluid-replacement beverage would alterintestinal fluid absorption from the duodenum and/or jejunumduring 85 min of cycle exercise (63.3 ± 0.9% peakO₂ uptake) in a cool environment(22°C), seven subjects (5 men, 2 women, peakO₂ uptake = 54.5 ± 3.8 ml · kg¹ · min¹) participated infour experiments separated by 1 wk in which they ingested a waterplacebo (WP) or one of three 6% carbohydrate (CHO) beveragesformulated to give mean osmolalities of 197, 295, or 414 mosmol/kgH₂O. CHO solutions alsocontained 17-18 meq Na⁺ and3.2 meq K⁺. Nasogastric andmultilumen tubes were fluoroscopically positioned in the gastric antrumand duodenojejunum, respectively. Subjects ingested a total of 23 ml/kgbody mass of the test solution, 20% (370 ± 9 ml) of this volume 5 min before exercise and 10% (185 ± 4 ml) every 10 min thereafter.By using the rate of gastric emptying as the rate of intestinalperfusion (G. P. Lambert, R. T. Chang, D. Joensen, X. Shi, R. W. Summers, H. P. Schedl, and C. V. Gisolfi. Int. J. Sports Med. 17: 48-55, 1996), intestinal absorption was determined by segmental perfusion from the duodenum (0-25 cm) and jejunum (25-50 cm). There were no differences(P > 0.05) in gastric emptying (mean18.1 ± 1.3 ml/min) or total fluid absorption (802 ± 109, 650 ± 52, 674 ± 62, and 633 ± 74 ml · 50 cm¹ · h¹for WP, hypo-, iso-, and hypertonic solutions, respectively) amongbeverages; but WP was absorbed faster(P < 0.05) from the duodenum than inthe jejunum. Of the total volume of fluid ingested, 82 ± 14, 74 ± 6, 76 ± 5, and 68 ± 7% were absorbed forWP, hypo-, iso-, and hypertonic beverages, respectively. There were nodifferences in urine production or percent change in plasma volumeamong solutions. We conclude that total fluid absorption of 6%CHO-electrolyte beverages from the duodenojejunum during exercise,within the osmotic range studied, is not different from WP.