Intracellular pH regulates basolateral K⁺ and Cl⁻ conductances in colonic epithelial cells by modulating Ca²⁺ activation

The role of intracellular pH as a modulator of basolateral K⁺ and Cl⁻ conductances in epithelial cells was studied using digitonin-permeabilized colonic cell layers so that cytosolic pH could be clamped at specific values, while basolateral K⁺ and Cl⁻ conductances were activated by stepwise increases in intracellular free Ca²⁺. Increasing the intracellular pH from 6.6 to 8.0 enhanced the sensitivity of both ionic conductances to intracellular Ca²⁺, but changing extracellular pH had no effect. Maximal K⁺ and Cl⁻ currents activated by Ca²⁺ were not affected by changes in intracellular pH, suggesting that protons do not alter the conduction properties of the channels. Hill analysis of the Ca²⁺ activation process revealed that raising the cytosolic pH from 6.6 to 8.0 reduced the K_1/2 for Ca²⁺ activation. In the absence of Ca²⁺, changes in intracellular pH did not have a significant effect on the basolateral K⁺ and Cl⁻ conductances. These results are consistent with the notion that changes in cytosolic pH can modulate basolateral conductances by modifying the action of calcium, perhaps by acting at or near the activation site to provide a mechanism of variable "gain control."