Na, Cl, and water transport by rat colon

Segments of the colon of anesthetized rats have been perfused in vivo with isotonic NaCl solutions and isotonic mixtures of NaCl and mannitol. Unidirectional and net fluxes of Na and Cl and the net fluxes of water and mannitol have been measured. Net water transport was found to depend directly on the rate of net Na transport. There was no water absorption from these isotonic solutions in the absence of net solute transport, indicating that water transport in the colon is entirely a passive process. At all NaCl concentrations studied, the lumen was found to be electrically negative to the surface of the colon by 5 to 15 mv. Na fluxes both into and out of the lumen were linear functions of NaCl concentration in the lumen. Net Na absorption from lumen to plasma has been observed to take place against an electrochemical potential gradient indicating that Na is actively transported. This active Na transport has been interpreted in terms of a carrier model system. Cl transport has been found to be due almost entirely to passive diffusion.

Rates of insorption of sodium and potassium from upper small bowel of rats

Rates of insorption of radiosodium and radiopotassium from the unobstructed small bowel of rats were determined and compared with those obtained by others in healthy humans. Insorption of the isotopes under study was estimated by integration of their rates of appearance in the blood after placement in the small bowel and their rates of disappearance from blood after injection into the circulation. The rates of disappearance from arterial blood were determined during separate tests. They followed an exponential pattern similar though not identical with that reported from other species by other investigators. Radiosodium was insorbed more rapidly than radiopotassium. Mean values indicated that 50% of administered radiosodium was insorbed within 6–7 min, whereas 26–27 min were required for insorption of 50% of the radiopotassium. The rate constant during insorption of the first 76% of the Na22 was 10.8% per min and that for insorption of 58% of the K42 was 2.7% per min.

Action of external divalent ion reduction on sodium movement in the squid giant axon

Voltage clamp measurements of the sodium potential have been made on the resting squid giant axon to study the effect of variations in external divalent ion concentration upon net sodium flux. From these measurements the intracellular sodium concentration and the net sodium inflow were calculated using the Nernst relation and constant activity coefficients. While an axon bathed in artificial sea water shows a slow increase in internal sodium concentration, the rate of sodium accumulation is increased about two times by reducing external calcium and magnesium concentrations to 0.1 times their normal values. The mean inward net sodium flux increases from a mean control value of 97 pmole/cm² sec. to 186 pmole/cm² sec. in low divalent solution. Associated with these effects of external divalent ion reduction are a marked decrease in action potential amplitude, little or no change in resting potential, and a shift along the voltage axis of the curve relating peak sodium conductance to membrane potential similar to that obtained by Frankenhaeuser and Hodgkin (1957). These results implicate divalent ions in long term (minutes to hours) sodium permeability.

Effect of vasopressin structural modifications on rat renal excretion of Na, K, and water

Lys8-vasopressin was incubated with trypsin, chymotrypsin, and sodium thioglycollate, and the resultant modification of the effect of the hormone on sodium, potassium, and water excretion was studied. These agents, which destroy the antidiuretic-pressor activity of the hormone, also bring about a loss of its natriuretic and kaliuretic effects. The action of Arg8-vasopressin, Phe2-Lys8-vasopressin, and His2-Lys8-vasopressin on sodium, potassium, and water excretion was studied; comparisons were made with the effects of equivalent pressor doses of Lys8-vasopressin. No significant differences between Arg8- and Lys8-vasopressin were obtained. Phe2-Lys8-vasopressin had nearly ten times the antidiuretic effect and four times the natriuretic and kaliuretic effect. Even though His2-Lys8-vasopressin has an antidiuretic effect, it lacks activity with regard to blood pressure or electrolyte excretion.