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

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 approximately -20 mV, reaches the peak at approximately +20 mV, has an inactivation time constant of 132.5 ± 5.6 msec at 20 mV, and is sensitive to dihydropyridines. The other is transient, activates at approximately - 40 mV, peaks at approximately -10 mV, has an inactivation time constant of 38.8 ± 1.8 msec at -10 mV, displays a voltage-dependent inactivation, and is sensitive to 100 μM Ni2+, but not to dihydropyridines. Biophysical and pharmacological properties of these currents indicate that they are gated through L- and T-type calcium channels, respectively. The cholinergic receptor agonist carbachol (50 μM) reduces the amplitude of the currents through both L-type (- 34.7 ± 6.4%; n = 10) and T-type (- 52.6 ± 7.4%; n = 8) channels, suggesting a possible role of these channels in the cholinergic regulation of human ovarian functions.