Low extracellular Ca2+ activates a transient Cl- current in chicken ovarian granulosa cells

The effects of low Ca2+ on ion currents in hen ovarian granulosa cells were examined. A fast activating and inactivating transient outward current (TOC) and a slowly activating outward current (SOC) could be observed. In the presence of normal Ca2+ concentration (2.5 mM) and with a holding potential of -80 mV, SOC was activated in all cells with command pulses more positive than -20 mV. In 2.5 mM Ca2+, TOC appeared in 10% of cells at the command pulse of +80 mV and in 60-85% of cells at +100 to +120 mV. In low-Ca2+ solution and command potential of +80 mV (holding potential of 280 mV), the amplitude of TOC was enhanced in cells that expressed it in normal Ca2+, and TOC appeared in 43% of the cells that did not express it initially in normal Ca2+. At both normal and low Ca2+ levels, TOC decreased as the holding potential became more positive. TOC was reduced in Cl--deficient solution and in the presence of 5-nitro-2-(3-phenylpropylamino)benzoic acid, a Cl- channel blocker. These findings suggest that chicken granulosa cells express a Ca2+-inactivated TOC carried by Cl-. This current may serve as a signal for some of the reduced metabolic functions of granulosa cells associated with Ca2+ deficiency.