Inhibition of Ca(2+)-dependent Cl- channels from secretory epithelial cells by low internal pH.

The actions of intracellular pH (pHi) on Ca(2+)-dependent Cl- channels were studied in secretory epithelial cells derived from human colon carcinoma (T84) and in isolated rat parotid acinar cells. Channel currents were measured with the whole cell voltage clamp technique with pipette solutions of different pH. Ca(2+)-dependent Cl- channels were activated by superfusing ionomycin to increase the intracellular calcium concentration ([Ca2+]i) or by using pipette solutions with buffered Ca2+ levels. Large currents were activated in T84 and parotid cells by both methods with pHi levels of 7.3 or 8.3. Little or no Cl- channel current was activated with pHi at 6.4. We used on-cell patch clamp methods to investigate the actions of low pHi on single Cl- channel current amplitude in T84 cells. Lowering the pHi had little or no effect on the current amplitude of a 8 pS Cl- channel, but did reduce channel activity. These results suggest that cytosolic acidification may be able to modulate stimulus-secretion coupling in fluid-secreting epithelia by inhibiting the activation of Ca(2+)-activated Cl- channels.