A possible correlation between ATPase activity and Na content of embryonic chick heart

The water content of embryonic chick ventricles decreases gradually from 88% at 2 days of incubation to 83% shortly after hatching. Ventricular protein nitrogen decreases during early development and then increases rapidly at midfetal age until hatching, after which a more gradual increase continues. Magnesium-activated ATPase activity of whole ventricle homogenates at pH 7.0–7.5 is much greater than is the calcium-activated enzyme throughout development. A very marked increase in Mg-ATPase occurs between 4 and 7 days of incubation; a lesser increase occurs just prior to and after hatching. Calcium-ATPase increases gradually throughout development. Magnesium-ATPase has been identified with both isolated mitochondrial and microsomal fractions; Ca-ATPase is exclusively associated with the myosin fraction. Myokinase occurs in the supernatant. Optimal pH's are given for the enzymes. It is suggested that the initial rapid fall in ventricular Na content between 2 and 7 days of incubation is directly related to two events: disappearance of the cardiac jelly and establishment of an effective Na extrusion mechanism.

Sodium and potassium ion effluxes from squid axons under voltage clamp conditions

Squid giant axons loaded with Na(24) were subjected to short duration (0.5 msec.) clamped depolarizations of about 100 mv at frequencies of 20/sec. and 60/sec. while in choline sea water. Under such conditions the early outward current was just about maximal at the time of termination of the clamping pulse. An integration of the early current versus time record gave 1.2 mucoulomb/cm(2) pulse, while a measurement of the extra Na(24) efflux resulting from repetitive pulsing gave a charge transfer of 1.4 mucoulomb/cm(2) pulse. In sodium-containing sea water and with pulses 50-75 mv more positive than E(Na) the Na(24) efflux is about 3 times the measured charge transfer. The efflux of K(42) from a previously loaded axon into normal sea water is only 50 per cent of the measured charge transfer when the membrane is held for about 5 msec. at a potential such that there is no early current, and such pulses are at 10-20/sec. The experiments appear to confirm the suggestion that the early current during bioelectric activity is sodium but provide unsatisfactory support for the identification of the delayed but sustained current solely with potassium ions. Resting Na(+) efflux is 0.6 pmole/cm(2) sec. mmole [Na](1), while the apparent K(+) efflux is about 250 pmole/cm(2) sec. and is little affected by hyperpolarization.

Salt saving in the pregnant rat

Pregnant rats of two strains showed average net accumulation of approximately 83 mEq of sodium/kg of weight gain throughout gestation. Of the total sodium retention, 15, 23, and 62% occurred in each successive third of gestation. Analysis of postpartum sodium balance and of fetal sodium content at term indicated that there was no net accumulation of sodium in the tissues of the dams. Near term, rats given isotonic saline solution showed diminished ability to excrete the administered water in the urine, but showed no impairment in sodium excretion. Serum sodium concentrations were slightly decreased and serum osmolalities were significantly decreased in comparison to values for nonpregnant rats. At term the pregnant rats had greater extracellular fluid volumes than did nonpregnant controls.

Intestinal electrolyte absorption by parallel determination of unidirectional sodium and water transfers

Plasma-to-lumen, lumen-to-plasma and net transfer rates for both sodium and water have been determined on dogs with Thiry-Vella loops, using a single transit perfusion. The net and lumen-to-plasma transfer rates of sodium are proportional to the concentration of sodium in the intestinal perfusate; net absorption of sodium ion occurs at all luminal sodium concentrations above 32 mEq/l. Water net transfer rate is inversely proportional to luminal osmolality; net absorption of water takes place at all luminal osmolalities up to 400 mOs/l. Hence, water must be actively transported and not transported exclusively as a passive osmotic consequence of sodium movement. Lumen-to-plasma water-transfer rates do not show a clear-cut osmotic dependency, owing to correlated sodium and water transfers. The regression slope of sodium on water transfer rates indicates the one-way transfer of an extremely dilute solution (42 mEq/l.), and this is true regardless of the composition of solution in the lumen. Such a phenomenon is a clear description of a fluid circuit mechanism.

Effect of hypothalamic lesions on renal excretion of sodium

Electrolytic hypothalamic lesions in the area of the paraventricular nuclei were followed by a threefold increase in urinary sodium excretion during the 24-hour period after operation. Renal denervation or bilateral adrenalectomy did not modify this response. Total hypophysectomy reduced but did not abolish the natriuresis. Paraventricular lesions reversed the antinatriuresis which normally follows depletion of extracellular fluid volume. The lesions had no apparent effect on potassium excretion.