Carbon monoxide stimulates a potassium-selective current in rabbit corneal epithelial cells

The effects of CO on ion currents in freshly dispersed rabbit corneal epithelial cells were assessed using the perforated patch whole cell voltage-clamp technique. Bath perfusion with 1% CO resulted in a 84 +/- 18% (mean +/- SE, n = 14) increase in potassium current (IK) and a membrane hyperpolarization from -42 +/- 4 to -51 +/- 4 mV. The CO-stimulated current reversed at -64 +/- 7 mV [reverse potential (EK) = -87 mV]. The stimulated current was blocked by 1 mM quinidine or 1 mM diltiazem, agents that inhibit IK in rabbit corneal epithelial cells. Single potassium-channel currents measured in the cell-attached configuration showed that exogenous CO increased the steady-state open probability from 0.003 to 0.156 at a holding potential of -40 mV. CO did not affect open probability in excised patches. The single-channel conductance measured from -40 to +40 mV was unaffected. Intracellular guanosine 3',5'-cyclic monophosphate (cGMP) concentration measured with radioimmunoassay techniques was found to increase from 0.41 +/- 0.24 to 0.55 +/- 0.27 pmol/10(6) cells after the addition of 1% CO (P < 0.05). The data show that bath perfusion with exogenous CO activates IK and hyperpolarizes the resting membrane potential; the data also suggest that CO modulates intracellular cGMP concentration.