Intracellular pH modulates ion channel activity in lacrimal gland acinar cells

The effects of intracellular pH on ion channel activity in lacrimal gland acinar cells were examined. The activity of Ca(2+)-activated K+ channels was studied in inside-out patches with bath pH at 7.8 and 6.8 (Ca2+ was buffered at 100 nM with EGTA). Elevating the bath pH to 7.8 increased channel open probability at each potential examined. The conductance of the channels was not affected by pH. The effects of pH on both K+ and Cl- channels were further investigated in whole-cell experiments. Increasing pH from 6.8 to 7.8 caused an increase in the current observed at hyperpolarising and depolarising potentials. The increase in outward currents at depolarising potentials was due to the increased activity of both K+ and Cl- channels. The activation of Cl- channels probably accounted for the increase in inward current at hyperpolarising potentials. This hypothesis was tested by examining whole-cell Cl- currents in the absence of permeant cations (i.e. K+ and Na+ replaced by N-methyl-D-glucamine). Under these conditions an increase in both inward and outward Cl- current was observed at pH 7.8. These data suggest that increasing intracellular pH increases the activity of Ca(2+)-activated K+ channels and Ca(2+)-activated Cl- channels.