Effects of pH on the potassium current in rabbit corneal epithelial cells

The effects of pH on K+ conductance were measured using the amphotericin perforated-patch whole cell voltage-clamp technique in freshly dispersed rabbit corneal epithelial cells. Bath perfusion with pH 6.00 Ringer solution after standard Ringer solution (pH 7.35) increased outward K+-selective current (I(K)) from 120 +/- 29 to 312 +/- 64 pA during a step depolarization to +50 mV and hyperpolarized the resting membrane potential (Em) from -52 +/- 5 to -62 +/- 3 mV (n = 15, P < or = 0.05). Increasing bath pH to 8.5 decreased I(K) from 183 +/- 40 to 114 +/- 35 pA (n = 6, P < or = 0.05) and depolarized Em from -63 +/- 6 to -53 +/- 5 mV (n = 6, P < or = 0.05). Intracellular acidification using the weak electrolyte (NH4)2SO4 also increased I(K) from 83 +/- 15 to 183 +/- 20 pA (n = 4, P = 0.01) and hyperpolarized Em from -51 +/- 8 to -68 +/- 6 mV (P = 0.002). Intracellular alkalinization reduced I(K) to 66 +/- 10 pA and depolarized Em to -36 +/- 8 mV (P = 0.009). Single channel studies in perforated outside-out vesicles showed that a decrease in bath pH from 7.35 to 6.00 was accompanied by an increase in the single channel open probability (NPo) from 0.43 to 0.64 at an Em of 15 mV. NPo was also increased in cell-attached patches. The unitary conductance, measured from -100 to +100 mV, was not changed. These results indicate that pH modulates I(K) in rabbit corneal epithelial cells by changes in NPo.