Two Types of Calcium Channels in Human Ovarian Endocrine Cells: Involvement in Steroidogenesis

Nature, regulation, and functional role of ion channels of human ovarian endocrine cells are not well known. In our present study, we show two types of voltage-activated Ca2+ currents (ICa) in cultured human luteinized granulosa cells (GCs), as assessed by whole-cell patch-clamp experiments. Electrophysiological properties, namely low threshold of activation, pronounced time-dependent inactivation, slow and voltage-dependent deactivation kinetics, insensitivity to SNX-482, and high sensitivity to Ni2+, defined the predominant ICa as a T-type Ca2+ current (ICa.T). In 4% of cells a Ni2+-insensitive ICa was measured alone or together with ICa.T. This Ca2+ current was high voltage activated and highly sensitive to dihydropyridine, indicative of an L-type Ca2+ current. RT-PCR analysis demonstrated the presence of mRNA coding for α1-subunits of two different Ca2+ channels (T-type Cav3.2 and L-type Cav1.2) in GCs. In addition, these two types were detected in the human corpus luteum by RT-PCR (Cav3.2) and immunohistochemistry (Cav1.2). Although stimulation of cultured GCs with human chorionic gonadotropin did not change the characteristics of recorded ICa.T, it markedly increased the percentage of cells displaying ICa from 29 to 63% and significantly increased (2.2-fold) the density of ICa.T. Furthermore, the stimulatory effect of human chorionic gonadotropin on progesterone production was diminished by pharmacological blockage of ICa.T by Ni2+ or flunarizine. Thus, our study provides evidence that human GCs in vivo and in vitro express T- and L-type Ca2+ channels and that the Cav3.2 (also called α1H) isoform is involved in a fundamental endocrine function of these cells.