2 TYPES OF STRETCH-ACTIVATED CHANNELS COEXIST IN THE RABBIT CORNEAL EPITHELIAL-CELL

Ion channels contribute to the regulation of cellular function through control of the membrane potential and intracellular concentration of various ions. We examined stretch-activated channels in the corneal ep ithelial cell. Patch clamping was applied to enzymatically dissociated corneal epithelial cells to characterize their stretch-activated ion channels. The plasma membrane was stretched by applying suction to the patch pipette in cell-attached or inside-out patch configuration. The ion selectivity, voltage-dependence, and stretch-dependence were exam ined. Two kinds of stretch-activated channel events were observed; the previously-reported large conductance (L) channel and a novel small c onductance (S) channel. The probability of recording L vs. S channels in the cell-attached configuration was about 2:1, The L channel was po tassium selective with single channel conductance (gamma) of about 160 pS under the symmetrical (150 mM K+) solution, The S channel was perm eable to Na+ and K+ with gamma of about 20 pS under the same condition s. Both L and S channels showed little activity in the absence of suct ion applied to the recording pipette. Channel activity was evoked by s uction (negative pressure) stronger than -20 mmHg in both channels. Th e open probability (P-0) and the mean current increased in proportion to further applied stretch and did not saturate for applied suction as strong as -80 mmHg, the pressure at which the gigaseal started to bre ak. Thus, two types of stretch-activated channels coexist in corneal e pithelial cells: a potassium-selective L channel and non-selective S c hannel. The contribution of these channels to the membrane potential i s discussed. (C) 1997 Academic Press Limited.