The effects of calcium on potassium transport in ferret red cells.

1. The effects of changes in the concentration of intracellular calcium on potassium transport were investigated in ferret red cells. Bumetanide was used to divide potassium transport into three components: total, bumetanide sensitive and bumetanide resistant. The bumetanide-sensitive component is equivalent to sodium-potassium-chloride co-transport. 2. Internal calcium concentration was controlled with the ionophore A23187 which was present throughout the experiments. 3. Changes in internal ionized calcium over the range 5 X 10(-10) M to 7 X 10(-7) M did not affect any component of potassium uptake. 4. Increasing the internal ionized calcium concentration above 10(-6) M stimulated bumetanide-resistant potassium transport. Half-maximal stimulation of this system was achieved with 3 X 10(-6) M-internal calcium. The system spontaneously inactivated after the initial activation by calcium and ionophore. Transport was inhibited by 1 mM-quinine. 5. Increasing the internal ionized calcium concentration to 10(-5) M had no effect on bumetanide-sensitive transport. 6. Concentrations of intracellular ionized calcium above 10(-5) M inhibited all three components of transport. Inhibition of the bumetanide-sensitive component was only slightly reversed when internal calcium concentration was reduced to normal. 7. Physiological changes in internal ionized calcium concentration do not affect sodium-potassium-chloride co-transport in ferret red cells. Very high concentrations of calcium inhibit transport, probably by an indirect mechanism. 8. In the course of the experiments the concentration of ionized intracellular magnesium in oxygenated ferret red cells was found to be about 0.65 mM.