Previous studies have shown that the resting potential (Em) of the corneal endothelium hyperpolarizes following an increase in temperature above 24 degrees C. Whole-cell studies using the perforated-patch technique were used to compare currents and Em values from isolated corneal endothelial cells at 24 and 32 degrees C. These studies revealed a small, outwardly rectifying, slowly activating, weakly voltage-dependent current with a reversal potential showing K+ selectivity (Erev = -80 mV). This current had features similar to the whole-cell current seen following addition of HCO3- to these cells. Em measurements 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 (Po) of a K+ channel previously reported in this cell type to be activated by external anions. Po (-30 mV) at 24 and 32 degrees C equaled 0.003 and 0.06, respectively. Increases in Po were found at all voltages examined. This increased Po can 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 Po along with an increased hyperpolarization of the cell, pointing to separate mechanisms of activation from these two stimuli.