Ion channel involvement in the temperature-sensitive response of the rabbit corneal endothelial cell resting membrane potential

Previous studies have shown that the resting potential (E_m) of the corneal endothelium hyperpolarizes following an increase in temperature above 24°C. Whole-cell studies using the perforated-patch technique were used to compare currents and E_mvalues from isolated corneal endothelial cells at 24 and 32°C. These studies revealed a small, outwardly rectifying, slowly activating, weakly voltage-dependent current with a reversal potential showing K⁺ selectivity (E_rev = –80 mV). This current had features similar to the whole-cell current seen following addition of HCO₃^– to these cells. E_mmeasurements found an average 24 mV hyperpolarization following temperature elevation in NaCl Ringer. Single channel studies found the only change in channel activity following an elevation in temperature to be an increase in the open probability (P_o) of a K⁺ channel previously reported in this cell type to be activated by external anions. P_o(–30 mV) at 24 and 32°C equaled 0.003 and 0.06, respectively. Increases in P_owere found at all voltages examined. This increased P_ocan account for the magnitude of the hyperpolarization seen in these cells following temperature elevation. Addition of HCO₃^– along with elevated temperature produced a synergistic effect on the increase in P_oalong with an increased hyperpolarization of the cell, pointing to separate mechanisms of activation from these two stimuli.The authors would like to thank Ms. Helen Hendrickson for her technical support and Drs. Gianrico Farrugia and Adam Rich for their helpful comments. This work was supported by NIH grants EY09673, EY03282, EY06005, and an unrestricted award from Research to Prevent Blindness.