Exercise reduces airway sodium ion reabsorption in cystic fibrosis but not in exercise asthma.

When ventilating large volumes of air during exercise, airway fluid secretion is essential for airway function. Since these are impaired in cystic fibrosis and exercise-induced asthma, it was the aim of this study to determine how exercise affects airway Na(+) and Cl(-) transport and whether changes depend on exercise intensity. Nasal potential was measured in Ringer's solution, with amiloride to block Na(+) transport, and in low chloride-containing isoproterenol to assess Cl(-) channels. Nasal potential was measured at rest and during submaximal and maximal bicycle ergometer exercise in individuals with cystic fibrosis, exercise-induced asthma and controls. At rest, nasal potential was significantly higher in cystic fibroses than in the others. Maximal exercise decreased nasal potentials in cystic fibrosis and controls but not in exercise asthma. Submaximal exercise decreased nasal potentials only in cystic fibrosis. Cl(-) transport was not affected. Our results indicate that nasal potentials and Na(+) transport were decreased by maximal exercise in healthy and cystic fibrosis, whereas submaximal exercise decreased potentials in cystic fibrosis only. Exercise did not affect nasal potentials in asthmatics. Decreased reabsorption during exercise might favour airway fluid secretion during hyperpnoea. This protective effect appears blunted in patients with exercise-induced asthma.

No evidence for interstitial lung oedema by extensive pulmonary function testing at 4,559 m.

The aim of the present study was to better understand previously reported changes in lung function at high altitude. Comprehensive pulmonary function testing utilising body plethysmography and assessment of changes in closing volume were carried out at sea level and repeatedly over 2 days at high altitude (4,559 m) in 34 mountaineers. In subjects without high-altitude pulmonary oedema (HAPE), there was no significant difference in total lung capacity, forced vital capacity, closing volume and lung compliance between low and high altitude, whereas lung diffusing capacity for carbon monoxide increased at high altitude. Bronchoconstriction at high altitude could be excluded as the cause of changes in closing volume because there was no difference in airway resistance and bronchodilator responsiveness to salbutamol. There were no significant differences in these parameters between mountaineers with and without acute mountain sickness. Mild alveolar oedema on radiographs in HAPE was associated only with minor decreases in forced vital capacity, diffusing capacity and lung compliance and minor increases in closing volume. Comprehensive lung function testing provided no evidence of interstitial pulmonary oedema in mountaineers without HAPE during the first 2 days at 4,559 m. Data obtained in mountaineers with early mild HAPE suggest that these methods may not be sensitive enough for the detection of interstitial pulmonary fluid accumulation.

Platelet count and function at high altitude and in high-altitude pulmonary edema.

Platelet aggregation is the key process in primary hemostasis. Certain conditions such as hypoxia may induce platelet aggregation and lead to platelet sequestration primarily in the pulmonary microcirculation. We investigated the influence of high-altitude exposure on platelet function as part of a larger study on 30 subjects with a history of high-altitude pulmonary edema (HAPE) and 10 healthy controls. All participants were studied in the evening and the next morning at low altitude (450 m) and after an ascent to high altitude (4,559 m). Platelet count, platelet aggregation (platelet function analyzer PFA100; using epinephrine and ADP as activators), plasma soluble P (sP)-selectin, and the coagulation parameters prothrombin fragments 1+2 and thrombin-antithrombin complex were measured. High-altitude exposure decreased the platelet count, shortened the platelet function analyzer closure time by approximately 20%, indicating increased platelet aggregation, increased sP-selectin levels to approximately 250%, but left plasma coagulation unaffected. The HAPE-susceptible subjects were prophylactically treated with either tadalafil (a phosphodiesterase 5 inhibitor), dexamethasone, or placebo in a double-blind way. Subgroup analyses between these different treatments and comparisons of the seven placebo-treated individuals developing HAPE and controls revealed no differences in platelet count, platelet aggregation, or sP-selectin values. We conclude that exposure to high altitude activates platelets, which leads to platelet aggregation, platelet consumption, and decreased platelet count. These effects are, however, not more pronounced in individuals with a history of HAPE or actually suffering from HAPE than in controls and therefore may not be a pathophysiological mechanism of HAPE.

Internal magnesium, 2,3-diphosphoglycerate, and the regulation of the steady-state volume of human red blood cells by the Na/K/2Cl cotransport system.

This study is concerned with the relationship between the Na/K/Cl cotransport system and the steady-state volume (MCV) of red blood cells. Cotransport rate was determined in unfractionated and density-separated red cells of different MCV from different donors to see whether cotransport differences contribute to the difference in the distribution of MCVs. Cotransport, studied in cells at their original MCVs, was determined as the bumetanide (10 microM)-sensitive 22Na efflux in the presence of ouabain (50 microM) after adjusting cellular Na (Nai) and Ki to achieve near maximal transport rates. This condition was chosen to rule out MCV-related differences in Nai and Ki that might contribute to differences in the net chemical driving force for cotransport. We found that in both unfractionated and density-separated red cells the cotransport rate was inversely correlated with MCV. MCV was correlated directly with red cell 2,3-diphosphoglycerate (DPG), whereas total red cell Mg was only slightly elevated in cells with high MCV. Thus intracellular free Mg (Mgifree) is evidently lower in red cells with high 2,3-DPG (i.e., high MCV) and vice versa. Results from flux measurements at their original MCVs, after altering Mgifree with the ionophore A23187, indicated a high Mgi sensitivity of cotransport: depletion of Mgifree inhibited and an elevation of Mgifree increased the cotransport rate. The apparent K0.5 for Mgifree was approximately 0.4 mM. Maximizing Mgifree at optimum Nai and Ki minimized the differences in cotransport rates among the different donors. It is concluded that the relative cotransport rate is regulated for cells in the steady state at their original cell volume, not by the number of copies of the cotransporter but by differences in Mgifree. The interindividual differences in Mgifree, determined primarily by differences in the 2,3-DPG content, are responsible for the differences in the relative cotransport activity that results in an inverse relationship with in vivo differences in MCV. Indirect evidence indicates that the relative cotransport rate, as indexed by Mgifree, is determined by the phosphorylated level of the cotransport system.

Red cell oxygen transport in man in relation to gender and age.

P50 values, the O2-partial pressure at 50% O2-saturation of hemoglobin, 2,3-DPG, hematological parameters and the plasma concentrations of sexual hormones were determined in 135 subjects of both sexes aged from 10 to 60 years. P50 was significantly higher in sexually mature women than in men, but did not differ between sexes before puberty and after menopause. In females P50 increased with sexual maturation by about 2 mmHg (0.27 kPa). RBC, Hb and Hct remained unchanged. In males Hb-O2-affinity, RBC, Hb and Hct increased with aging. In sexually mature females 2,3-DPG was significantly higher (2 mumol/gHb) than in males, although before puberty and postmaturity no difference was found. In males, 2,3-DPG increased slightly with maturation although P50 decreased. P50 values (pH = 7.4) correlated positively with red cell 2,3-DPG only when data from all groups were pooled (r = 0.330, P less than or equal to 0.0001). Hb was negatively correlated with P50 (r = 0.221, P less than or equal to 0.01). The data suggest a sex hormone and maturation induced influence in the development of the red cell O2-transport system. Estrogens seem to favour a decrease in Hb-O2-affinity rather than an elevation in O2-transport capacity, whereas androgens do the reverse.

Red blood cells do not contribute to removal of K+ released from exhaustively working forearm muscle.

K+ released from exercising muscle via K+ channels needs to be removed from the interstitium into the blood to maintain high muscle cell membrane potential and allow normal muscle contractility. Uptake by red blood cells has been discussed as one mechanism that would also serve to regulate red blood cell volume, which was found to be constant despite increased plasma osmolality and K+ concentration ([K+pl]). We evaluated exercise-related changes in [K+pl], pH, osmolality, mean cellular Hb concentration, cell water, and red blood cell K+ concentration during exhaustive handgrip exercise. Unidirectional 86Rb+ (K+) uptake by red blood cells was measured in media with elevated extracellular K+, osmolarity, and catecholamines to simulate particularly those exercise-related changes in plasma composition that are known to stimulate K+ uptake. During exercise [K+pl] increased from 4.4 +/- 0.7 to 7.1 +/- 0.5 mmol/l plasma water and red blood cell K+ concentration increased from 137.2 +/- 6.0 to 144.6 +/- 4.6 mmol/l cell water (P

Interactions between Hb, Mg, DPG, ATP, and Cl determine the change in Hb-O2 affinity at high altitude.

Ascent to high altitude (HA) causes an increase in erythrocyte 2,3-diphsophoglycerate (DPG) and standard PO2 at 50% O2 saturation, PCO2 40 Torr, and blood pH 7.4 (P50,st). We studied the early phase of acclimatization to HA of mountaineers without and with a history of HA pulmonary edema. Tests were performed before ascent and after arrival at HA (4,559 m), approximately 22 h after the departure from low altitude (HA1) and on the following 3 days at HA (HA2-HA4). We investigated the relation between changes in DPG and P50,st, since at moderate altitude P50,st increases more rapidly than DPG, indicating that other factors may contribute to the change in P50,st. Combined effects of interaction between allosteric effectors of hemoglobin (Hb) (DPG, ATP, Cl) and Mg, which competes with Hb for DPG and ATP binding, might explain that phenomenon. Therefore concentrations of liganded Hb species were calculated from the total erythrocyte concentrations of the ligands by use of published binding constants and were related to changes in Hb-O2 affinity. P50,st increased at HA by approximately 4.5 Torr; the concentration of total DPG and ATP increased by 28 and 19%, respectively. Whereas P50,st reached a plateau already at HA1, the concentration of DPG reached its highest value at HA4. The erythrocyte Cl concentration decreased, whereas cellular Hb and Mg concentrations increased slightly. The sum of concentrations of all liganded Hb species increased, reaching 79% of its total change within 22 h after ascent; this can mainly be attributed to the change in the concentration of Hb[DPG] (+77% of total increase).(ABSTRACT TRUNCATED AT 250 WORDS)

Unchanged in vivo P50 at high altitude despite decreased erythrocyte age and elevated 2,3-diphosphoglycerate.

We measured hematological and erythrocyte O2 transport parameters in whole blood and density-separated erythrocytes in 11 mountaineers before and during 5 days of exposure to high altitude (4,559 m). We determined the in vivo (arterial pHblood and PCO2) and standard (pHblood = 7.4, PCO2 = 40 Torr) O2 tension at 50% O2 saturation of hemoglobin and (P50,vv and P50,st) and Bohr coefficients (BC) for fixed acid (H+) and CO2 and examined the contribution of the altered average age of circulating erythrocytes due to the stimulation of erythropoiesis on whole blood 2,3-diphosphoglycerate (2,3-DPG) and P50,st. At altitude, whole blood P50,vv remained almost unchanged, whereas P50,st and 2,3-DPG increased significantly (+4 Torr; 3.5 mumol/g hemoglobin). BCCO2 was elevated significantly at altitude. Serum erythropoietin increased transiently fourfold, iron utilization increased, and serum iron decreased by 66%. Reticulocyte counts increased, but other hematological parameters were unchanged. In density-separated erythrocytes, P50,st and 2,3-DPG increased with decreasing cell density but were higher in fractions with comparable reticulocyte counts in cells prepared at altitude than in those from control studies. Our data show that, despite the increase in 2,3-DPG and the decrease in average erythrocyte age, the in vivo hemoglobin-O2 affinity remains unchanged. P50,st values reflect the elevation of 2,3-DPG, and approximately 50% of the increase in both parameters can be ascribed to the increase in the number of reticulocytes and young erythrocytes.

Effects of iron repletion on blood volume and performance capacity in young athletes.

PURPOSE: The purpose of this study was to find out whether iron repletion leads to an increase in red blood cell volume (RBV) and performance capacity in iron-deficient nonanemic athletes. METHODS: 40 young elite athletes (13-25 yr) with low serum ferritin (< 20 microg.L-1) and normal hemoglobin (males > 13.5 g.dL-1, females > 11.7 g.dL-1) were randomly assigned to 12-wk treatment with either twice a day ferrous iron (equivalent to 2 x 100 mg elemental iron) or with placebo using a double blind method. Before and after treatment, hematological measures and parameters of iron status were determined in venous blood. RBV, blood volume (BV), and plasma volume (PV) were measured by CO rebreathing. For determination of the aerobic and anaerobic capacity (maximal accumulated oxygen deficit, MAOD), the athletes performed an incremental as well as a highly intensive treadmill test. RESULTS: After 12 wk, ferritin levels were within the normal range in the iron-treated group (IG) with a significant (P < 0.001) mean increase by 20 microg.L-1 opposed to a slight nonsignificant decrease in the placebo group (PG). RBV did not change significantly in either group nor did any of the hematological measures. However, only in IG there were significant increases in VO2max and in O2 consumption in the MAOD test. MAOD and maximal capillary lactate concentration remained unchanged in both treatment groups. CONCLUSIONS: The results indicate that in young elite athletes with low serum ferritin and normal hemoglobin concentration iron supplementation leads to an increase in maximal aerobic performance capacity without an augmentation of RBV.

Lack of effect of oral Mg-supplementation on Mg in serum, blood cells, and calf muscle.

UNLABELLED: Magnesium (Mg) is important for regulating ion transport and cellular metabolism in all body tissues. In skeletal muscle Mg is involved in the neuromuscular activity, excitation, and muscle contraction. Mg deficiency can cause muscle weakness and muscle cramps. Less than 1% of total body Mg is found in serum, yet the serum Mg concentration is used to assess the body's Mg status. PURPOSE: The purpose of this study was to determine whether an oral Mg supplementation (500 mg Mg-oxide.d-1 for 3 wk) affects exercise performance, clinical symptoms, and the Mg concentration in various body compartments in athletes with low-normal serum Mg levels (N = 10 in each group). METHODS: In a double-blind, placebo-controlled study, correlation analysis between the Mg concentration in serum, blood cells, and skeletal muscle was performed to establish a measure for muscle cell Mg. RESULTS: The data indicate that a 3-wk Mg supplementation did not affect exercise performance, neuromuscular activity, or muscle related symptoms. Also, the supplementation did not increase the Mg concentration in serum or any cellular compartment studied. However, in the placebo group the renal Mg clearance decreased, whereas it increased in the subjects receiving Mg supplementation. Correlation analysis revealed that serum Mg only correlated with red cell Mg and that only leukocyte Mg correlated with the nuclear magnetic resonance (NMR)-measured muscle cell Mg concentration. CONCLUSIONS: These results indicate that Mg supplementation in athletes with low-normal serum Mg did not improve performance and failed to increase the body's Mg stores. Serum Mg appears to be a poor indicator for Mg in skeletal muscle or most other cellular compartments, but the concentration of Mg in mononuclear leukocytes might be used as an indicator of skeletal muscle Mg when NMR is not available.

Increase in Hb-O2-affinity at moderate altitude (2000 m) in patients on maintenance hemodialysis.

Oxygen transport by erythrocytes was studied in eight patients on maintenance hemodialysis before, during and after a 2-week stay at an altitude of 2000 m. Dialysis was continued at that altitude. In all tests, blood samples were collected one or two days following hemodialysis. Pre-altitude tests: The patients exhibited anemia (hemoglobin concentration, Hb = 97.4 +/- 17 g/l). Due to an elevated red cell 2,3-diphosphoglycerate concentration (2,3-DPG) and mild metabolic acidosis, elevated standard and in vivo P50 values (pO2 at 50% oxygen saturation of hemoglobin, sO2) were measured. Altitude: Upon ascent, arterial pO2 decreased from 82 +/- 4 torr to about 60 torr, sO2 was lowered by 5%. After 2 weeks sojourn, pO2 and sO2 increased towards normal values. In contrast to healthy subjects, dialysis patients developed respiratory alkalosis (blood pH: +0.074) upon ascent. This caused a significant shift to the left of the oxygen dissociation curve (ODC), indicated by lowered in vivo P50-values (P50,vv,-2 torr). Red cell 2,3-DPG, P50,st (P50 at a blood pH = 7.4 and pCO2 = 40 torr), hemoglobin concentration and hematocrit showed a high day-to-day variability and did not change because of the altitude exposure. We interpret the increase of the oxygen affinity of hemoglobin in patients with renal anemia as beneficial, as it favors oxygen loading of hemoglobin in the lung during exposure to a hypoxic environment.

Exercise performance of hemodialysis patients during short-term and prolonged exposure to altitude.

The work capacity of patients on maintenance hemodialysis is impaired even at normal inspiratory oxygen pressure. A further restriction can be expected when these patients are exposed to hypoxia at altitude, since most of the usual compensatory mechanisms required to adjust to this environment are impaired or even missing. We tested the tolerance of hemodialysis patients to hypoxia and measured work capacity, hematological, and cardiovascular parameters at rest and during incremental bicycle ergometry during 3-hour exposure to altitudes of 2,000 m and 3,000 m, and during 2 weeks of exposure to an altitude of 2,000 m and compared these data with prealtitude values or with data evaluated in a control group, respectively. In control tests the patients reached work loads at exercise termination of about 66% of age and sex-matched healthy controls, the reduction correlated well with the degree of anemia. During short-term altitude exposure to 2,000 m peak work performance remained unchanged in comparison to prealtitude tests, whereas at 3,000 m it was reduced by about 12%. During the 2-week stay at 2,000 m peak work loads increased significantly by 17% accompanied by an increase in peak oxygen uptake (+15%), blood lactate, heart rates (+10 min-1), and systolic blood pressure (+20 mmHg), whereas the diastolic pressure was comparable to prealtitude values. In another group of hemodialysis patients studied at low altitude under similar experimental conditions none of these parameters was changed. Our data show that during acute exposure to altitudes up to 2,000 m maximal work of hemodialysis patients is not reduced, but is restricted at altitudes higher than that.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pseudo-anemia caused by sports]. / Pseudoanämie durch Sport.

Regular physical training leads to an increase of plasma volume by 10-20 percent. Therefore, hemoglobin concentration slightly below normal values in the presence of low-normal serum ferritin levels in athletes are usually due to a dilutional "pseudoanemia". Several cross sectional studies indicate that true iron deficiency anemia is not more frequent in athletes than in the general population. Since regular physical activity, especially extensive, running increases iron loss, mild iron deficiency (abnormal serum ferritin and normal hemoglobin concentration) and sometimes true iron deficiency anemia can occur especially when nutritional iron intake is insufficient and iron demand is increased because of growth (children, adolescents) or additional iron loss (menstruation). Several controlled studies indicate that iron supplementation (recommended dose 2 x 100 mg elementary iron/day) improves performance only when hemoglobin concentration increases, i.e. when iron deficiency anemia is present. On the contrary, iron supplementation has no measurable effects on performance when hemoglobin concentration cannot be increased, i.e. in mild iron deficiency.

[Acute mountain sickness and high-altitude pulmonary edema. How to protect the mountain climber from the effects of the "altitude haze"]. / Akute Bergkrankheit und Höhenlungenödem. Wie Sie Bergsteiger vor den Folgen des "Höhenrauschs" bewahren.

Acute mountain sickness (AMS) usually occurs after 6-12 hours of acute exposure to altitudes above 2,500 m. If there is no further altitude gain, it normally resolves spontaneously within a day or two. However, it may, in rare cases, progress to life-threatening cerebral edema. High-altitude pulmonary edema (HAPE) is a non-cardiogenic edema that is often preceded by symptoms of AMS. The major preventive measure is slow ascent. Acetazolamide and dexamethasone are effective in preventing AMS, while nifedipine is effective only against HAPE. Immediate descent and/or the administration of oxygen is the treatment of choice for both conditions. If this is not possible, dexamethasone may be given for severe AMS and nifedipine for HAPE.

Evidence supportive of impaired myocardial blood flow reserve at high altitude in subjects developing high-altitude pulmonary edema.

An exaggerated increase in pulmonary arterial pressure is the hallmark of high-altitude pulmonary edema (HAPE) and is associated with endothelial dysfunction of the pulmonary vasculature. Whether the myocardial circulation is affected as well is not known. The aim of this study was, therefore, to investigate whether myocardial blood flow reserve (MBFr) is altered in mountaineers developing HAPE. Healthy mountaineers taking part in a trial of prophylactic treatment of HAPE were examined at low (490 m) and high altitude (4,559 m). MBFr was derived from low mechanical index contrast echocardiography, performed at rest and during submaximal exercise. Among 24 subjects evaluated for MBFr, 9 were HAPE-susceptible individuals on prophylactic treatment with dexamethasone or tadalafil, 6 were HAPE-susceptible individuals on placebo, and 9 persons without HAPE susceptibility served as controls. At low altitude, MBFr did not differ between groups. At high altitude, MBFr increased significantly in HAPE-susceptible individuals on treatment (from 2.2 +/- 0.8 at low to 2.9 +/- 1.0 at high altitude, P = 0.04) and in control persons (from 1.9 +/- 0.8 to 2.8 +/- 1.0, P = 0.02), but not in HAPE-susceptible individuals on placebo (2.5 +/- 0.3 and 2.0 +/- 1.3 at low and high altitude, respectively, P > 0.1). The response to high altitude was significantly different between the two groups (P = 0.01). There was a significant inverse relation between the increase in the pressure gradient across the tricuspid valve and the change in myocardial blood flow reserve. HAPE-susceptible individuals not taking prophylactic treatment exhibit a reduced MBFr compared with either treated HAPE-susceptible individuals or healthy controls at high altitude.

Hypoxia causes permeability oedema in the constant-pressure perfused rat lung.

Alveolar hypoxia causes pulmonary oedema associated with increased lung capillary pressure and decreased alveolar fluid reabsorption. However, the role of altered permeability is unclear. The aim of the present study was to test whether hypoxia affects alveolar permeability and induces pulmonary oedema in rat lungs, and whether terbutaline affects oedema formation. Isolated lungs of normoxic rats were perfused at a constant pressure (12 cmH2O) and exposed to different levels of oxygenation (1.5-35% O2). Terbutaline (10-5 M) was applied as an aerosol or with the perfusate. Online measurements indicate an earlier onset of weight gain with an increasing degree of hypoxia and a shortened lung survival time (35% O2: approximately 220 min; 1.5% O2: approximately 120 min). Terbutaline did not prevent oedema formation in hypoxic lungs. The terbutaline-induced formation of cyclic adenosine monophosphate was decreased by 50% in hypoxia (1.5% O2). In experiments terminated after 75 min, bronchoalveolar lavage fluid of hypoxic lungs contained protein that originated from perfusate indicating alveolar leakage. Since lactate dehydrogenase in perfusate was not increased at the onset of oedema formation, cell damage does not explain the increased permeability. In conclusion, these results indicate the formation of a leak for macromolecules of the isolated perfused rat lung, which is accelerated by hypoxia and causes alveolar flooding even at low perfusion pressure at a rate that exceeds absorption even after stimulation with terbutaline.

Red blood cell function in hypoxia at altitude and exercise.

Oxygen transport by red blood cells is regulated by erythropoiesis and Hb-O2-affinity. The O2 carrying capacity is characterized by changes in hematocrit, red blood count or the mass of circulating red blood cells. Erythropoiesis is controlled by the hormone erythropoietin, which induces slow changes of the O2-transport capacity. The Hb-O2-affinity is modified mainly by pH and 2,3-DPG. Despite their apparently diverse effects e.g. in hypoxia at high altitude, a compromise seems to be adopted optimizing both arterial O2-loading and peripheral O2-unloading. In contrast to erythropoiesis, adjustments of the Hb-O2-affinity occur fast and allow rapid adjustments of O2-binding and release. In the intact organism the significance of changes in Hb-O2-affinity for tissue oxygen supply relative to adjustments of cardiac output, microcirculation and O2-transport capacity is not completely understood yet, but beneficial effects were demonstrated in isolated organs. It is, however, the least energy-demanding way of optimizing tissue O2-supply, which might be of significance in extreme situations. In severe hypoxia adjustments of both, hematocrit and Hb-O2-affinity, are insufficient to maintain tissue O2-supply. Alterations of Hb-O2-affinity are also insufficient to compensate for severe anemia.

Na(+)-K(+)-2Cl- cotransport, Na+/H+ exchange, and cell volume in ferret erythrocytes.

Ferrets have high-Na+ and low-K+ erythrocytes (113 and 5.4 mmol/l cell water) due to the lack of Na(+)-K+ pumps. Because ferret erythrocytes have a high capacity for Na(+)-K(+)-2Cl- cotransport, the present study was undertaken to evaluate cell volume-related changes in cotransport activity and its role in volume regulation. With cell shrinkage, Na(+)-K(+)-2Cl- cotransport is activated about twofold. A large bumetanide-insensitive Na+ uptake component that has not yet been described is found in shrunken erythrocytes. Its inhibition by amiloride (concn inhibiting 50% of maximal response = 12 microM) and the Na+ dependence of amiloride-sensitive extracellular pH changes measured in cells suspended in hypertonic unbuffered medium indicate that this flux represents Na+/H+ exchange. Shrinkage activation of both transporters follows a time lag of approximately 3 min and also requires normal levels of ATP. ATP depletion inhibits Na(+)-K(+)-2Cl- cotransport even at normal cell volume. Both transporters are partially inhibited by the protein kinase inhibitors staurosporine and K252a, and activators of protein kinases A and C do not affect transport. Okadaic acid inhibition of protein phosphatases activates Na(+)-K(+)-2Cl- cotransport to its maximal activity (same after shrinkage), but shrinkage and okadaic acid activation are not additive. In contrast, okadaic acid activates Na+/H+ exchange even in shrunken cells. These results indicate that cell shrinkage activates Na(+)-K(+)-2Cl- cotransport and Na+/H+ exchange probably by phosphorylation processes.

Diminution of the temperature effects on the oxygen affinity of hemoglobin after prolonged hypothermia.

The influence of temperature on the oxygen affinity of hemoglobin, expressed as half saturation tension P50, was investigated in male Sprague Dawley rats, which had been exposed to a cold environment for about 12 h. P50-values were determined by equilibrating blood samples to a known PO2 at different temperatures. The well known increase in oxygen affinity at low temperatures was observed, but after a longer hypothermic period this effect was diminished. This reduction of the temperature effect is manifested in a change of the ratio delta log P50/delta T from 0.022 in control experiments to 0.0115 in hypothermia. In cold adapted rats such an effect means a better oxygen supply to tissue at low body temperatures than in control animals. These changes in oxygen delivery after cold acclimatisation may partially be interpreted as the result of the decreased intraerythrocytic pH and elevated concentration of ATP found in the present study.