Membrane currents of porcine granulosa cells in primary culture: Characterization and effects of luteinizing hormone

Abstract

In ovarian granulosa cells, LH depolarizes the membrane potential and induces steroid production. The membrane currents of porcine granulosa cells in primary culture were studied by means of the whole-cell configuration of the patch-clamp technique to investigate whether the ionic channels are involved in the effects of LH. We identified and characterized two types of K+ currents-a transient outward current (I(to)) and a delayed rectifier K+ current (I(K))-and one Ca2+ current (I(Ca)). I(to) and I(K) were voltage- and calcium-dependent. Both currents were blocked by 4-aminopyridine, a K+ channel blocker, but only I(K) was sensitive to tetraethylammonium, another K+ channel blocker. I(Ca) was inactivated within 50 ms of the test pulse. Nifedipine and verapamil, L-type CA2+ channel blockers, did not suppress I(Ca) even at a concentration of 10 μM. Tetramethrin (1 μM), a T-type Ca2+ channel blocker, decreased I(Ca) by 38.4 ± 5.6% (n = 3). These findings suggest that the current may be a T-type Ca2+ current. LH and dibutyryl cAMP, potent stimulants of steroid production, attenuated I(to) only by 13.9 ± 1.8% (n = 7) and 21.0 ± 1.5% (n = 4), respectively. However, they did not affect I(K) and I(Ca). These results indicated that LH does not modulate CA2+ current directly, but it slightly decreased I(to) through cAMP elevation. The LH-induced inhibition of I(to) may be involved in the depolarizing effect of LH and may play some role in steroid secretion or other functions in granulosa cells.