Basal lamina of ovarian follicle regulates an inward Cl- current in differentiated granulosa cells

Patch-clampexperiments were conducted to study the effects of basal lamina(basement membrane) of preovulatory chicken ovarian follicle onmembrane currents in differentiated chicken granulosa cells in ahomologous system. The membrane capacitance (measure of total membranearea) was smaller in cells cultured on intact basal lamina than that ofcontrol cells. The granulosa cells expressed outward and two inwardcurrents. A small fraction of the cells (3%) expressed only atransient fast-activating and -inactivating inward current carried byCa²⁺. The majority of the cells, however, expressed aslowly activating and inactivating inward current (carried byCl) that was superimposed on the transientCa²⁺ current. All cells expressed an outward currentcharacteristic of the delayed-rectifier K⁺ current. Theremoval of extracellular Ca²⁺ led to elimination of theslow inward Cl current, indicating that it is aCa²⁺-dependent Cl current. Both peakamplitude and current density of the inward Cl currentwere significantly lower in cells cultured on freshly isolated intactbasal lamina (or basal lamina stored at 4°C for 12 mo) than those ofcontrol cells; however, basal lamina had no significant effect on thedensity of the outward current. Similar to the observations made forintact basal lamina, solubilized basal lamina suppressed the inwardCl current in differentiated granulosa cells. These datashow that homologous basal lamina modulates aCa²⁺-dependent Cl current in differentiatedgranulosa cells. These findings provide a partial explanation for themechanisms that subserve the reported effects of basal lamina (basementmembrane) on the metabolic functions of differentiated granulosa cells.