Thermal and metabolic responses to cold-water immersion at knee, hip, and shoulder levels

Lee, Dae T., Michael M. Toner, William D. McArdle, IoannisS. Vrabas, and Kent B. Pandolf. Thermal and metabolic responses tocold-water immersion at knee, hip, and shoulder levels.J. Appl. Physiol. 82(5):1523-1530, 1997.To examine the effect of cold-water immersion atdifferent depths on thermal and metabolic responses, eight men (25 yrold, 16% body fat) attempted 12 tests: immersed to the knee (K), hip(H), and shoulder (Sh) in 15 and 25°C water during both rest (R) orleg cycling [35% peak oxygen uptake; (E)] for up to 135 min. At 15°C, rectal (T_re)and esophageal temperatures(T_es) between R and E were notdifferent in Sh and H groups (P > 0.05), whereas both in K group were higher during E than R(P < 0.05). At 25°C,T_re was higher(P < 0.05) during E than R at alldepths, whereas T_es during E washigher than during R in H and K groups.T_re remained at control levels inK-E at 15°C, K-E at 25°C, and in H-E groups at 25°C,whereas T_es remained unchanged inK-E at 15°C, in K-R at 15°C, and in all 25°C conditions (P > 0.05). During R and E, themagnitude of T_re change wasgreater (P < 0.05) than themagnitude of T_es change in Sh andH groups, whereas it was not different in the K group(P > 0.05). Total heat flow wasprogressive with water depth. During R at 15 and 25°C, heatproduction was not increased in K and H groups from control level(P > 0.05) but it did increase in Shgroup (P < 0.05). The increase inheat production during E compared with R was smaller(P < 0.05) in Sh (121 ± 7 W/m² at 15°C and 97 ± 6 W/m² at 25°C) than in H (156 ± 6 and 126 ± 5 W/m²,respectively) and K groups (155 ± 4 and 165 ± 6 W/m², respectively). These datasuggest that T_re andT_es respond differently duringpartial cold-water immersion. In addition, water levels above knee in15°C and above hip in 25°C cause depression of internal temperatures mainly due to insufficient heat production offsetting heatloss even during light exercise.

     

Effect of ingested sodium bicarbonate on muscle force, fatigue, and recovery

Verbitsky, O., J. Mizrahi, M. Levin, and E. Isakov.Effect of ingested sodium bicarbonate on muscle force, fatigue, and recovery. J. Appl. Physiol. 83(2):333-337, 1997.The influence of acute ingestion ofNaHCO₃ on fatigue and recovery ofthe quadriceps femoris muscle after exercise was studied in six healthymale subjects. A bicycle ergometer was used for exercising under three loading conditions: test A, loadcorresponding to maximal oxygen consumption; testB, load in test A + 17%; test C, load intest B but performed 1 h after acuteingestion of NaHCO₃.Functional electrical stimulation (FES) was applied to provokeisometric contraction of the quadriceps femoris. The resulting kneetorque was monitored during fatigue (2-min chronic FES) and recovery (10-s FES every 10 min, for 40 min). Quadriceps torques were higher inthe presence of NaHCO₃(P < 0.05): withNaHCO₃ the peak, residual, andrecovery (after 40 min) normalized torques were, respectively, 0.68 ± 0.05 (SD), 0.58 ± 0.05, and 0.73 ± 0.05; withoutNaHCO₃ the values were 0.45 ± 0.04, 0.30 ± 0.06, and 0.63 ± 0.06. The increasedtorques obtained after acute ingestion ofNaHCO₃ indicate the possibleexistence of improved nonoxidative glycolysis in isometric contraction,resulting in reduced fatigue and enhanced recovery.

     

Hypohydration effects on skeletal muscle performance and metabolism: a 31P-MRS study

The purpose of this study was to determinewhether hypohydration reduces skeletal muscle endurance and whetherincreased H⁺ andP_i might contribute to performancedegradation. Ten physically active volunteers (age 21-40 yr)performed supine single-leg, knee-extension exercise to exhaustion in a1.5-T whole body magnetic resonance spectroscopy (MRS) system wheneuhydrated and when hypohydrated (4% body wt).³¹P spectra were collected at arate of one per second at rest, exercise, and recovery, and weregrouped and averaged to represent 10-s intervals. The desired hydrationlevel was achieved by having the subjects perform 2-3 h ofexercise in a warm room (40°C dry bulb, 20% relative humidity)with or without fluid replacement 3-8 h before the experiment.Time to fatigue was reduced (P < 0.05) by 15% when the subjects were hypohydrated [213 ± 12 vs. 251 ± 15 (SE) s]. Muscle strength was generally notaffected by hypohydration. Muscle pH andP_i/-ATP ratio were similarduring exercise and at exhaustion, regardless of hydration state. The time constants for phosphocreatine recovery were also similar betweentrials. In summary, moderate hypohydration reduces muscle endurance,and neither H⁺ norP_i concentration appears to berelated to these reductions.

     

Ultrasound evaluation of piglet diaphragm function before and after fatigue

Kocis, Keith C., Peter J. Radell, Wayne I. Sternberger, JaneE. Benson, Richard J. Traystman, and David G. Nichols. Ultrasound evaluation of piglet diaphragm function before and after fatigue. J. Appl. Physiol. 83(5):1654-1659, 1997.Clinically, a noninvasive measure of diaphragmfunction is needed. The purpose of this study is to determine whetherultrasonography can be used to 1)quantify diaphragm function and 2)identify fatigue in a piglet model. Five piglets were anesthetized withpentobarbital sodium and halothane and studied during the followingconditions: 1) baseline (spontaneous breathing); 2) baseline + CO₂ [inhaledCO₂ to increase arterial PCO₂ to 50-60 Torr (6.6-8kPa)]; 3) fatigue + CO₂ (fatigue induced with 30 minof phrenic nerve pacing); and 4)recovery + CO₂ (recovery after 1 hof mechanical ventilation). Ultrasound measurements of the posteriordiaphragm were made (inspiratory mean velocity) in the transverseplane. Images were obtained from the midline, just inferior to thexiphoid process, and perpendicular to the abdomen. M-mode measures weremade of the right posterior hemidiaphragm in the plane just lateral tothe inferior vena cava. Abdominal and esophageal pressures weremeasured and transdiaphragmatic pressure (Pdi) was calculated duringspontaneous (Sp) and paced (Pace) breaths. Arterial blood gases werealso measured. Pdi(Sp) and Pdi(Pace)during baseline + CO₂ were 8 ± 0.7 and 49 ± 11 cmH₂O, respectively, anddecreased to 6 ± 1.0 and 27 ± 7 cmH₂O,respectively, during fatigue + CO₂. Mean inspiratory velocityalso decreased from 13 ± 2 to 8 ± 1 cm/s during theseconditions. All variables returned to baseline during recovery + CO₂. Ultrasonography can beused to quantify diaphragm function and identify piglet diaphragm fatigue.

     

Furosemide reduces accumulated oxygen deficit in horses during brief intense exertion

Hinchcliff, K. W., K. H. McKeever, W. W. Muir, and R. A. Sams. Furosemide reduces accumulated oxygen deficit inhorses during brief intense exertion. J. Appl.Physiol. 81(4): 1550-1554, 1996.We theorizedthat furosemide-induced weight reduction would reduce the contributionof anaerobic metabolism to energy expenditure of horses during intenseexertion. The effects of furosemide on accumulatedO₂ deficit and plasma lactateconcentration of horses during high-intensity exercise were examined ina three-way balance randomized crossover study. Nine horses completedeach of three trials: 1) a control(C) trial, 2) a furosemide-unloaded(FU) trial in which the horse received furosemide 4 h before running, and 3) a furosemide weight-loaded(FL) trial during which the horse received furosemide and carriedweight equal to the weight lost after furosemide administration. Horsesran for 2 min at ~120% maximalO₂ consumption. Furosemide (FU)increased O₂ consumption (ml ^· 2 min^{1 ·} kg¹)compared with C (268 ± 9 and 257 ± 9, P < 0.05), whereas FL was notdifferent from C (252 ± 8). AccumulatedO₂ deficit (ml O₂ equivalents/kg) wassignificantly (P < 0.05) lowerduring FU (81.2 ± 12.5), but not during FL (96.9 ± 12.4), thanduring C (91.4 ± 11.5). Rate of increase in blood lactateconcentration (mmol ^· 2 min^{1 ·} kg¹)after FU (0.058 ± 0.001), but not after FL (0.061 ± 0.001), was significantly (P < 0.05) lower than after C (0.061 ± 0.001). Furosemide decreased theaccumulated O₂ deficit and rate ofincrease in blood lactate concentration of horses during briefhigh-intensity exertion. The reduction in accumulatedO₂ deficit in FU-treated horseswas attributable to an increase in the mass-specific rate ofO₂ consumption during thehigh-intensity exercise test.

     

Hypoxia, temperature, and pH/CO2 effects on respiratory discharge from a turtle brain stem preparation

Johnson, Stephen M., Rebecca A. Johnson, and Gordon S. Mitchell. Hypoxia, temperature, andpH/CO₂ effects on respiratory discharge from a turtle brain stem preparation. J. Appl. Physiol. 84(2): 649-660, 1998.An in vitrobrain stem preparation from adult turtles (Chrysemyspicta) was used to examine the effects of anoxia andincreased temperature and pH/CO₂on respiration-related motor output. At pH ~7.45, hypoglossal (XII)nerve roots produced patterns of rhythmic bursts (peaks) of discharge(0.74 ± 0.07 peaks/min, 10.0 ± 0.6 s duration) that werequantitatively similar to literature reports of respiratory activity inconscious, vagotomized turtles. Respiratory discharge was stable for 6 h at 22°C; at 32°C, peak amplitude and frequency progressivelyand reversibly decreased with time. Two hours of hypoxia had no effecton respiratory discharge. Acutely increasing bath temperature from 22 to 32°C decreased episode and peak duration and increased peakfrequency. Changes in pH/CO₂increased peak frequency from zero at pH 8.00-8.10 to maxima of0.81 ± 0.01 and 1.44 ± 0.02 peaks/min at 22°C (pH 7.32) and32°C (pH 7.46), respectively;pH/CO₂ sensitivity was similar atboth temperatures. We conclude that1) insensitivity to hypoxiaindicates that rhythmic discharge does not reflect gasping behavior,2) increased temperature altersrespiratory discharge, and 3)central pH/CO₂ sensitivity isunaffected by temperature in this preparation (i.e.,Q₁₀ ~1.0).

     

Hypohydration and thermoregulation in cold air

O'Brien, Catherine, Andrew J. Young, and Michael N. Sawka.Hypohydration and thermoregulation in cold air.J. Appl. Physiol. 84(1): 185-189, 1998.This study examined the effects of hypohydration onthermoregulation during cold exposure. In addition, the independentinfluences of hypohydration-associated hypertonicity and hypovolemiawere investigated. Nine male volunteers were monitored for 30 min at25°C, then for 120 min at 7°C, under three counterbalancedconditions: euhydration (Eu), hypertonic hypohydration (HH), andisotonic hypohydration (IH). Hypohydration was achieved 12 h beforecold exposure by inducing sweating (HH) or by ingestion of furosemide(IH). Body weight decrease (4.1 ± 0.2%) caused by hypohydrationwas similar for HH and IH, but differences(P < 0.05) were found between HH andIH in plasma osmolality (292 ± 1 vs. 284 ± 1 mosmol/kgH₂O) andplasma volume reduction (8 ± 2 vs. 18 ± 3%).Heat debt (349 ± 14 among) did not differ(P > 0.05) among trials. Mean skintemperature decreased throughout cold exposure during Eu but plateauedafter 90 min during HH and IH. Forearm-fingertemperature gradient tended (P = 0.06)to be greater during Eu (10.0 ± 0.7°C) than during HH or IH(8.9 ± 0.7°C). This suggests weaker vasoconstrictor tone duringhypohydration than during Eu. Final mean skin temperature was higherfor HH than for Eu or IH (23.5 ± 0.3, 22.6 ± 0.4, and 22.9 ± 0.3°C, respectively), and insulation was lower on HH than onIH (0.13 ± 0.01 vs. 0.15 ± 0.01°C · W¹ · m²,respectively), but not with Eu (0.14 ± 0.01°C · W¹ · m²).This provides some evidence that hypertonicity impairs the vasoconstrictor response to cold. Although mild hypohydration did notaffect body heat balance during 2-h whole body exposure to moderatecold, hypohydration-associated hypertonicity may have subtle effects onvasoconstriction that could become important during a more severe coldexposure.

     

Effects of supplemental oxygen on forearm vasodilation in humans

Crawford, Paul, Peter A. Good, Eric Gutierrez, Joshua H. Feinberg, John P. Boehmer, David H. Silber, and Lawrence I. Sinoway. Effects of supplemental oxygen on forearm vasodilation in humans.J. Appl. Physiol. 82(5):1601-1606, 1997.Supplemental O₂ reduces cardiac output andraises systemic vascular resistance in congestive heart failure. Inthis study, 100% O₂ was given tonormal subjects and peak forearm flow was measured. Inexperiment 1, 100%O₂ reduced blood flow andincreased resistance after 10 min of forearm ischemia (flow 56.7 ± 7.9 vs. 47.8 ± 6.7 ml · min¹ · 100 ml¹;P < 0.02; vascular resistance 1.7 ± 0.2 vs. 2.4 ± 0.4 mmHg · min · 100 ml · ml¹;P < 0.03). Inexperiment 2, lower body negativepressure (LBNP; 30 mmHg) and venous congestion (VC) simulatedthe high sympathetic tone and edema of congestive heart failure.Postischemic forearm flow and resistance were measured under fourconditions: room air breathing (RA); LBNP+RA; RA+LBNP+VC; and 100%O₂+LBNP+VC. LBNP and VC did notlower peak flow. However, O₂raised minimal resistance (2.3 ± 0.4 RA; 2.8 ± 0.5 O₂+LBNP+VC,P < 0.04). When O₂ alone(experiment 1) was compared withO₂+LBNP+VC(experiment 2), no effect of LBNP+VCon peak flow or minimum resistance was noted, although the return rateof flow and resistance toward baseline was increased.O₂ reduces peak forearm flow evenin the presence of LBNP and VC.

     

Effects of glucose, glucose plus branched-chain amino acids, or placebo on bike performance over 100km

Madsen, Klavs, Dave A. MacLean, Bente Kiens, and DirkChristensen. Effects of glucose, glucose plus branched-chain aminoacids, or placebo on bike performance over 100 km. J. Appl. Physiol. 81(6): 2644-2650, 1996.This studywas undertaken to determine the effects of ingesting either glucose(trial G) or glucose plusbranched-chain amino acids (BCAA; trialB), compared with placebo (trialP), during prolonged exercise. Nine well-trained cyclists with a maximal oxygen uptake of 63.1 ± 1.5 mlO₂ ^· min^{1 ·} kg¹performed three laboratory trials consisting of 100 km of cycling separated by 7 days between each trial. During these trials, the subjects were encouraged to complete the 100 km as fast as possible ontheir own bicycles connected to a magnetic brake. No differences inperformance times were observed between the three trials (160.1 ± 4.1, 157.2 ± 4.5, and 159.8 ± 3.7 min, respectively). Intrial B, plasma BCAA levels increased from339 ± 28 µM at rest to 1,026 ± 62 µM after exercise(P < 0.01). Plasma ammoniaconcentrations increased during the entire exercise period for allthree trials and were significantly higher intrial B compared withtrials G andP (P < 0.05). The respiratory exchange ratio was similar in the threetrials during the first 90 min of exercise; thereafter, it tended todrop more in trial P than intrials G andB. These data suggest that neitherglucose nor glucose plus BCAA ingestion during 100 km of cyclingenhance performance in well-trained cyclists.

     

Effects of NaHCO3 loading on acid-base balance, lactate concentration, and performance in racing greyhounds

This investigation examined the effects ofNaHCO₃ loading on lactateconcentration ([La]), acid-base balance, and performance for a 603.5-m sprint task. Ten greyhounds completed aNaHCO₃ (300 mg/kg body weight) andcontrol trial in a crossover design. Results are expressed as means ± SE. Presprint differences (P < 0.05) were found for NaHCO₃ vs.control, respectively, for blood pH (7.47 ± 0.01 vs. 7.42 ± 0.01), HCO₃ (28.4 ± 0.4 vs. 23.5 ± 0.3 meq/l), and base excess (5.0 ± 0.3 vs. 0.2 ± 0.3 meq/l). Peak blood [La] increased(P < 0.05) inNaHCO₃ vs. control (20.4 ± 1.6 vs. 16.9 ± 1.3 mM, respectively). Relative to control,NaHCO₃ produced a greater(P < 0.05) reduction in blood baseexcess (18.5 ± 1.4 vs. 14.1 ± 0.8 meq/l) andHCO₃ (17.4 ± 1.2 vs.12.8 ± 0.7 meq/l) from presprint to postexercise. Postexercise peak muscle H⁺concentration ([H⁺])was higher (P < 0.05) inNaHCO₃ vs. control (158.8 ± 8.8 vs. 137.0 ± 5.3 nM, respectively). Muscle[H⁺] recoveryhalf-time (7.2 ± 1.6 vs. 11.3 ± 1.6 min) and time to predosevalues (22.2 ± 2.4 vs. 32.9 ± 4.0 min) were reduced(P < 0.05) inNaHCO₃ vs. control, respectively.No differences were found in blood[H⁺] or blood[La] recovery curves or performance times.NaHCO₃ increased postexerciseblood [La] but did not reduce the muscle or blood acid-basedisturbance associated with a 603.5-m sprint or significantly affectperformance.

     

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.

     

Sodium alterations in isolated rat heart during cardioplegic arrest

Schepkin, V. D., I. O. Choy, and T. F. Budinger. Sodiumalterations in isolated rat heart during cardioplegic arrest. J. Appl. Physiol. 81(6):2696-2702, 1996.Triple-quantum-filtered (TQF) Na nuclearmagnetic resonance (NMR) without chemical shift reagent is used toinvestigate Na derangement in isolated crystalloid perfused rat heartsduring St. Thomas cardioplegic (CP) arrest. Theextracellular Na contribution to the NMR TQF signal of a rat heart isfound to be 73 ± 5%, as determined by wash-out experiments atdifferent moments of ischemia and reperfusion. With the use of thiscontribution factor, the estimated intracellular Na([Na⁺]_i)TQF signal is 222 ± 13% of preischemic level after 40 min of CParrest and 30 min of reperfusion, and the heart rate pressure productrecovery is 71 ± 8%. These parameters aresignificantly better than for stop-flow ischemia: 340 ± 20% and 6 ± 3%, respectively. At 37°C, the initial delay of 15 min in[Na⁺]_igrowth occurs during CP arrest along with reduced growth later (~4.0%/min) in comparison with stop-flow ischemia (~6.7%/min). The hypothermia (21°C, 40 min) for the stop-flow ischemia and CPdramatically decreases the[Na⁺]_igain with the highest heart recovery for CP (~100%). These studiesconfirm the enhanced sensitivity of TQF NMR to[Na⁺]_iand demonstrate the potential of NMR without chemical shift reagent tomonitor[Na⁺]_iderangements.

     

Effect of an 18-wk weight-training program on energy expenditure and physical activity

Van Etten, Ludo M. L. A., Klaas R. Westerterp, Frans T. J. Verstappen, Bart J. B. Boon, and Wim H. M. Saris. Effect of an18-wk weight-training program on energy expenditure and physicalactivity. J. Appl. Physiol. 82(1):298-304, 1997.The purpose of this study was to examine theeffect of an 18-wk weight-training program on average daily metabolicrate (ADMR). Before the intervention and in weeks8 and 18 (T₀,T₈, andT₁₈, respectively) data on bodycomposition, sleeping metabolic rate (SMR), food intake, energy cost ofthe weight-training program(EE_ex), and nontraining physicalactivity (accelerometer) were collected in the exercise group (EXER,n = 18 males). ADMR was determined ina subgroup (EX12, n = 12) by usingdoubly labeled water. At T₀ andT₁₈, data (except ADMR) were alsocollected in a control group (Con, n = 8). Body mass did not change in EXER or Con. Fat-free mass increased only in EXER with 2.1 ± 1.2 kg, whereas fat mass decreased in EXERas well as Con (2.0 ± 1.8 and 1.4 ± 1.0 kg, respectively). Initial ADMR (12.4 ± 1.2 MJ/day) increased atT₈ (13.5 ± 1.3 MJ/day, P < 0.001) with no further increaseat T₁₈ (13.5 ± 1.9 MJ/day). SMR did not change in EXER (4.8 ± 0.5, 4.9 ± 0.5, 4.8 ± 0.5 kJ/min) or Con (4.7 ± 0.4, 4.8 ± 0.4 kJ/min). Energy intake didnot change in EXER (10.1 ± 1.8, 9.7 ± 1.8, 9.2 ± 1.9 MJ/day) or Con (10.2 ± 2.6, 9.4 ± 1.8, 10.1 ± 1.5 MJ/day)and was systematically underreported in EX12 (21 ± 14, 28 ± 18, 34 ± 14%,P < 0.001).EE_ex (0.47 ± 0.20, 0.50 ± 0.18 MJ/day) could only explain 40% of the increase in ADMR.Nontraining physical activity did not change in both groups. Inconclusion, although of modest energy cost, weight-training induces asignificant increase in ADMR.

     

Endothelial cell dilatory pathways link flow and wall shear stress in an intact arteriolar network

Frame, Mary D. S., and Ingrid H. Sarelius. Endothelialcell dilatory pathways link flow and wall shear stress in an intactarteriolar network. J. Appl. Physiol.81(5): 2105-2114, 1996.Our purpose was to determine whether theendothelial cell-dependent dilatory pathways contribute to theregulation of flow distribution in an intact arteriolar network. Cellflow, wall shear stress (T),diameter, and bifurcation angle were determined for four sequentialbranches of a transverse arteriole in the superfused cremaster muscleof pentobaribtal sodium (Nembutal, 70 mg/kg)-anesthetized hamsters(n = 51). Control cell flow wassignificantly greater into upstream than into downstream branches[1,561 ± 315 vs. 971 ± 200 (SE) cells/s,n = 12]. Tissue exposure to 50 µMN-nitro-L-arginine + 50 µM indomethacin (L-NNA + Indo) produced arteriolar constriction of 14 ± 4% and decreasedflow into the transverse arteriole. More of the available cell flow wasdiverted to downstream branches, yet flow distribution remainedunequal. Control T was higherupstream than downstream (31.3 ± 6.8 vs. 9.8 ± 1.5 dyn/cm²).L-NNA + Indo decreasedT upstream and increasedT downstream to become equal inall branches, in contrast to flow. To determine whether constriction ingeneral induced the same changes, 5%O₂ (8 ± 4% constriction) or10⁹ M norepinephrine (NE;4 ± 3% constriction) was added to the tissue (n = 7). WithO₂, flow was redistributed tobecome equal into each branch. With NE, flow decreased progressivelymore into the first three branches. The changes in flow distributionwere thus predictable and dependent on the agonist. WithO₂ or NE, the spatial changes inflow were mirrored by spatial changes inT. Changes in diameter and incell flux were not related forL-NNA + Indo (r = 0.45),O₂(r = 0.07), or NE(r = 0.36). For all agonists, when thebifurcation angle increased, cell flow to the branch decreasedsignificantly, whereas if the angle decreased, flow was relativelypreserved; thus active changes in bifurcation angle may influence redcell distribution at arteriolar bifurcations. Thus, when theendothelial cell dilatory pathways were blocked, the changes in flowand in T were uncoupled; yet when they were intact, flowand T changed together.

     

Atrial natriuretic peptide levels and plasma volume contraction in acute alveolar hypoxia

Albert, T. S. E., V. L. Tucker, and E. M. Renkin.Atrial natriuretic peptide levels and plasma volume contraction in acute alveolar hypoxia. J. Appl.Physiol. 82(1): 102-110, 1997.Arterial oxygentensions (Pa_O2), atrial natriureticpeptide (ANP) concentrations, and circulating plasma volumes (PV) weremeasured in anesthetized rats ventilated with room air or 15, 10, or8% O₂(n = 5-7). After 10 min ofventilation, Pa_O2 values were 80 ± 3, 46 ± 1, 32 ± 1, and 35 ± 1 Torrand plasma immunoreactive ANP (irANP) levels were 211 ± 29, 229 ± 28, 911 ± 205, and 4,374 ± 961 pg/ml, respectively. AtPa_O2 40 Torr, irANP responses weremore closely related to inspiredO₂(P = 0.014) than toPa_O2 (P = 0.168). PV was 36.3 ± 0.5 µl/g in controls but 8.5 and9.9% lower (P  0.05) for10 and 8% O₂, respectively.Proportional increases in hematocrit were observed in animals withreduced PV; however, plasma protein concentrations were not differentfrom control. Between 10 and 50 min of hypoxia, small increases (+40%)in irANP occurred in 15% O₂;however, there was no further change in PV, hematocrit, plasma protein,or irANP levels in the lower O₂groups. Urine output tended to fall during hypoxia but was notsignificantly different among groups. These findings are compatiblewith a role for ANP in mediating PV contraction during acute alveolarhypoxia.

     

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.

     

Conservation of bronchiolar wall area during constriction and dilation of human airways

Mitchell, R. W., E. Rühlmann, H. Magnussen, N. M. Muñoz, A. R. Leff, and K. F. Rabe. Conservation ofbronchiolar wall area during constriction and dilation of humanairways. J. Appl. Physiol. 82(3):954-958, 1997.We assessed the effect of smooth musclecontraction and relaxation on airway lumen subtended by the internalperimeter(A_i)and total cross-sectional area (A_o)of human bronchial explants in the absence of the potential lungtethering forces of alveolar tissue to test the hypothesis thatbronchoconstriction results in a comparable change ofA_i andA_o.Luminal area (i.e.,A_i) andA_owere measured by using computerized videomicrometry, and bronchial wallarea was calculated accordingly. Images on videotape were captured;areas were outlined, and data were expressed as internal pixel numberby using imaging software. Bronchial rings were dissected in 1.0- to1.5-mm sections from macroscopically unaffected areas of lungs frompatients undergoing resection for carcinoma, placed in microplate wellscontaining buffered saline, and allowed to equilibrate for 1 h.Baseline, A_o[5.21 ± 0.354 (SE)mm²], andA_i(0.604 ± 0.057 mm²) weremeasured before contraction of the airway smooth muscle (ASM) withcarbachol. MeanA_inarrowed by 0.257 ± 0.052 mm²in response to 10 µM carbachol (P = 0.001 vs. baseline). Similarly, A_onarrowed by 0.272 ± 0.110 mm²in response to carbachol (P = 0.038 vs. baseline; P = 0.849 vs. change inA_i).Similar parallel changes in cross-sectional area forA_iandA_owere observed for relaxation of ASM from inherent tone of otherbronchial rings in response to 10 µM isoproterenol. We demonstrate aunique characteristic of human ASM; i.e., both luminal and totalcross-sectional area of human airways change similarly on contractionand relaxation in vitro, resulting in a conservation of bronchiolarwall area with bronchoconstriction and dilation.

     

Skeletal muscle chemoreflex and pHi in exercise ventilatory control

Oelberg, David A., Allison B. Evans, Mirko I. Hrovat, PaulP. Pappagianopoulos, Samuel Patz, and David M. Systrom. Skeletal muscle chemoreflex and pH_i inexercise ventilatory control. J. Appl.Physiol. 84(2): 676-682, 1998.To determinewhether skeletal muscle hydrogen ion mediates ventilatory drive inhumans during exercise, 12 healthy subjects performed three bouts ofisotonic submaximal quadriceps exercise on each of 2 days in a 1.5-Tmagnet for ³¹P-magnetic resonancespectroscopy(³¹P-MRS). Bilaterallower extremity positive pressure cuffs were inflated to 45 Torr duringexercise (BLPP_ex) or recovery(BLPP_rec) in a randomized orderto accentuate a muscle chemoreflex. Simultaneous measurements were madeof breath-by-breath expired gases and minute ventilation, arterializedvenous blood, and by ³¹P-MRS ofthe vastus medialis, acquired from the average of 12 radio-frequencypulses at a repetition time of 2.5 s. WithBLPP_ex, end-exercise minuteventilation was higher (53.3 ± 3.8 vs. 37.3 ± 2.2 l/min;P < 0.0001), arterializedPCO₂ lower (33 ± 1 vs. 36 ± 1 Torr; P = 0.0009), and quadricepsintracellular pH (pH_i) more acid (6.44 ± 0.07 vs. 6.62 ± 0.07; P = 0.004), compared withBLPP_rec. Bloodlactate was modestly increased withBLPP_ex but without a change inarterialized pH. For each subject, pH_i was linearly relatedto minute ventilation during exercise but not to arterialized pH. Thesedata suggest that skeletal muscle hydrogen ion contributes to theexercise ventilatory response.

     

Passive sensitization of human airways induces myogenic contractile responses in vitro

Mitchell, R. W., K. F. Rabe, H. Magnussen, and A. R. Leff.Passive sensitization of human airways induces myogenic contractile responses in vitro. J. Appl.Physiol. 83(4): 1276-1281, 1997.We assessedeffects of passive sensitization on human bronchial smooth muscle (BSM)response to mechanical stretching in vitro. Bronchial rings were sham(control) or passively sensitized overnight by using sera from donorsdemonstrating sensitivity to Dermatophagoides farinae and having immunoglobulin E (IgE)concentrations of 2,600 ± 200 U/ml. Tissues were fixedisometrically to force transducers to measure responses to electricalfield stimulation (EFS) and quick stretch (QS). The myogenic responseto QS was normalized to the maximal response to EFS (%EFS). Themyogenic response of sensitized BSM was 47.9 ± 10.9 %EFS to a QSof ~6.5% optimal length (L_o);sham-sensitized tissues had a myogenic response of 13.5 ± 6.4 %EFS(P = 0.012 vs. passively sensitized).A QS of ~13% L_o in sensitizedBSM caused a response of 82.8 ± 20.9 %EFS; sham-sensitized tissuesdeveloped a response of 38.2 ± 17.3 %EFS(P = 0.004). BSM incubated with serumfrom nonallergic donors did not demonstrate increased QS response (4.6 ± 1.4 %EFS, P = not significantvs. tissue exposed to atopic sera). However, tissues incubated in serafrom nonatopic donors supplemented with hapten-specific chimeric IgE(JW8) demonstrated augmented myogenic response to QS of ~6.5% L_o (21.9 ± 6.2 %EFS, P = 0.027 vs. nonatopicsera alone). We demonstrate that passive sensitization of human BSMpreparations causes induction and augmentation of myogenic contractionsto QS; this hyperresponsiveness corresponds to the IgE concentration insensitizing sera.

     

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.