H. Victor Murdaugh

Circulatory Adaptation to Diving in the Freshwater Turtle

The heart of the freshwater turtle has a functional ventricular septal defect. In ambient air there is some shunting of blood from the left to the right ventricle through the defect. During prolonged diving or N2 inhalation, the shunt is reversed and blood from the tissues bypasses the lung and enters the aorta directly. This adaptation appears to be based on the exclusive use of anaerobic glycolysis as an energy source during prolonged diving.

UREA: APPARENT CARRIER-MEDIATED TRANSPORT BY FACILITATED DIFFUSION IN DOGFISH ERYTHROCYTES.

The exposure of erythrocytes from the elasmobranch, Squalus acanthias, to solutions isosmotic with plasma (IM) but containing urea or hydroxyurea as the sole solute does not produce hemolysis. Exposure of these cells to IM methylurea, thiourea and acetamide does produce hemolysis. Low concentrations of urea, which are associated with hemolysis, protect dogfish red cells against hemolysis by methylurea and thiourea. Dogfish red cells exposed to mediums containing high concentrations of urea, or no urea, reach 95 percent of their equilibrium concentration in less than 5 minutes.

Humoral agent from calf lung producing pulmonary arterial vasoconstriction.

Saline washings obtained in vivo from the lung of young calves produce pulmonary hypertension upon intrayascular (systemic or pulmonary) injection into either the dog or the calf. This pulmonary hypertension is produced by vasoconstriction of small, precapillary pulmonary vessels. The active agent, pulmonary arterial constrictor substance, differs chemically and physiologically from other substances which have been investigated with respect to vasomotor activity in the pulmonary circulation. Although the chemical nature of the active agent is not known it appears to have a relatively large molecular weight. Whether this agent plays a role in the physiological regulation of the pulmonary circulation is not known.

Cation transport and energy metabolism in the high Na+, low K+ erythrocyte of the harbor seal, Phoca vitulina.

1. 1. Cation transport in relation to cell metabolism in the high Na+, low K+ seal erythrocyte was investigated. Under steady-state conditions at 40°C, Na+ efflux was32 ± 4·0 (S.D.) m-equiv. × kg RBC H2O−1 × hr−1and K+ influx was 1·1 ± 0·38m-equiv. × kg RBC H2O−1 × hr−1. 2. 2. Both fluxes were insensitive to ouabain (10−4 M) and an inhibitor of anaerobic metabolism, monoiodoacetate (10−4 M). 3. 3. Ethanol (5 × 10−1 M) decreased Na+ efflux in the seal erythrocyte and the high Na+, low K+ cat erythrocyte but did not affect Na+ transport in the low Na+, high K+ human erythrocyte. 4. 4. Valinomycin (10−5 M) produced increased permeability to K+ without effect on Na+ transport. 5. 5. Lactate production (2·4 ± 0·29 mM×1.RBC H2O−1 × hr−1) was not decreased significantly by ouabain. 6. 6. Adenosinetriphosphate (ATP) concentrations (0·4 ± 0·03 (S.D.)mM/5·0 mM Hb) and 2,3 diphosphoglycerate (2,3 DPG) concentrations (6·5 ± 0·53 (S.D.) mM/5·0 mM Hb) provide evidence that this cell possesses an active glycolytic mechanism for high energy phosphate production. 7. 7. Quantitatively, the level of energy transduction is similar in both high Na+, low K+ seal erythrocytes and low Na+, high K+ human erythrocytes despite the small calculated minimal work cost of cation transport in the former.

Role of Na-K-atpase in the renal reabsorption of sodium in the elasmobranch, squalus acanthias

Abstract 1. 1. The relative importance of Na-K-activated ATPase in active bulk transport of Na + in the elasmobranch kidney was examined. Fractional Na + excretion was examined before and after the administration of ouabain, associated with over a 60 per cent reduction in enzyme activity, as well as following furosemide and ethacrynic acid. 2. 2. Marked inhibition of Na-K-ATPase with ouabain did not reduce Na + reabsorption, in contrast to furosemide and ethacrynic acid which increased fractional excretion from 0·22 to 0·69. 3. 3. These data suggest that Na-K-ATPase does not participate in bulk transport of Na + in the elasmobranch kidney, where the conservation of Na + is of little importance in osmoregulation.

Cation transport and energy metabolism in the nucleated erythrocyte of the dogfish shark, Squalus acanthias☆

Abstract 1. 1. Electrolyte distribution in the nucleated erythrocyte of the dogfish shark, Squalus acanthias, resembles that found in low Na+-high K+ mammalian erythrocytes. 2. 2. Na+ efflux (20°C) averaged 14·9 ± 2·7 m-equiv × kg RBC H2O−1 × hr−1, being reduced significantly by monoiodoacetate (10−2 M), N2 exposure, and ouabain (10−4 M). 3. 3. K+ influx (20°C) averaged 9·1 ±4·0 m-equiv × kg RBC H2O−1× hr−1, being reduced significantly by exposure to 12°C and ouabain (10−4 M). 4. 4. Total O2 consumption (30°C) averaged 3·14 ± 0·76 mM × kg RBC H2O−1× hr−1. Sixty-five per cent of QO2 is related to ATP generation. 5. 5. Lactate production (30°C) averaged 1·52 mM × kg RBC H2O−1 × hr−1. Inhibition of oxidative phosphorylation produced a Pasteur effect. 6. 6. Total energy availability exceeds that required for cation transport, suggesting that other energy-consuming processes are present. A substantial amount of energy required for cation transport is presumably derived from oxidative phosphorylation.