Sodium, potassium and chloride intracellular concentrations in the intestine of the freshwater turtle Mauremys caspica.

Sodium, potassium and chloride intracellular concentrations were measured. Sodium replacement from the bathing medium induced a significant decrease in chloride intracellular concentration. Conversely, chloride replacement from the bathing medium induced a significant decrease in sodium intracellular concentration. These results suggest the existence of a coupled NaCl transport system. The presence of 10(-3) M ouabain in the bathing medium increased Na+ intracellular concentration while decreasing that of K+. Cyanide (10(-3) M) produced a significant increase in Na+ intracellular concentration, whereas that of K+ was not affected by this agent.