Membrane currents of porcine granulosa cells in primary culture: characterization and effects of luteinizing hormone.
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 (Ito) and a delayed rectifier K+ current (IK)--and one Ca2+ current (ICa). Ito and IK were voltage- and calcium-dependent. Both currents were blocked by 4-aminopyridine, a K+ channel blocker, but only IK was sensitive to tetraethylammonium, another K+ channel blocker. ICa was inactivated within 50 ms of the test pulse. Nifedipine and verapamil, L-type CA2+ channel blockers, did not suppress ICa even at a concentration of 10 microM. Tetramethrin (1 microM), a T-type Ca2+ channel blocker, decreased ICa 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 Ito only by 13.9 +/- 1.8% (n = 7) and 21.0 +/- 1.5% (n = 4), respectively. However, they did not affect IK and ICa. These results indicated that LH does not modulate CA2+ current directly, but it slightly decreased Ito through cAMP elevation. The LH-induced inhibition of Ito may be involved in the depolarizing effect of LH and may play some role in steroid secretion or other functions in granulosa cells.
Department of Obstetrics and Gynecology, Hokkaido University School of Medicine, Sapporo, Japan.
M
M
Kusaka
N
N
Tohse
H
H
Nakaya
T
T
Tanaka
M
M
Kanno
S
S
Fujimoto
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology; D005260:Female; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D013552:Swine
D015220:Calcium Channels; D015221:Potassium Channels; D007986:Luteinizing Hormone; D015761:4-Aminopyridine; D000242:Cyclic AMP