Voltage-activation of high-conductance K + channel in the insulin-secreting cell line RINm5F is dependent on local extracellular Ca 2+ concentration

Abstract

Patch-clamp single-channel current recording experiments have been carried out on intact insulin-secreting RINm5F cells. Voltage-activation of high-conductance K + channels were studied by selectively depolarizing the electrically isolated patch membrane under conditions with normal Ca 2+ concentration in the bath solution but with or without Ca 2+ in the patch pipette solution. When Ca 2+ was present in the pipette, 40 mV to 120 mV depolarizing pulses (100 ms) from the normal resting potential (−70 mV) regularly evoked tetraethylammonium-sensitive large outward single-channel currents and the average open state probability during the pulses varied from about 0.015 (40 mV pulses) to 0.1 (120 mV pulses). In the absence of Ca 2+ in the pipette solution the same protocol resulted in fewer and shorter K + channel openings and the open-state probability varied from about 0.0015 (40 mV pulses) to about 0.03 (120 mV pulses). It is concluded that Ca 2+ entering voltage-gated channels raises [Ca 2+] i locally and thereby markedly enhances the open-state probability of tetraethylammonium-sensitive voltage-gated high-conductance K + channels.