L- and T-type voltage-gated Ca2+ channels in human granulosa cells: functional characterization and cholinergic regulation.

Using the whole-cell configuration of the patch-clamp technique, we have characterized two types of ionic currents through voltage-dependent Ca2+ channels in human granulosa cells. One is long-lasting, activates at ~-20 mV, reaches the peak around +20 mV, has an inactivation time constant of 132.5 ms ± 5.6 ms at 20 mV and is sensitive to dihydropyridines. The other is transient, activates at ~-40 mV, peaks around -10mV, has an inactivation time constant of 38.8 ms ± 1.8 ms at -10 mV, displays a voltage-dependent inactivation and is sensitive to 100µM Ni2+, but not to dihydropyridines. Biophysical and pharmacological properties of these currents indicates that they are gated through L- and T-type calcium channels, respectively. The cholinergic receptor agonist carbachol (50µM) reduces the amplitude of the currents through both L- (- 35% ± 6.4; n=10) and T-type (- 53% ± 7.4; n=8) channels, suggesting a possible role of these channels in the cholinergic regulation of human ovarian functions.