[Comprehensive study on the membrane currents of porcine granulosa cells in culture].
The membrane currents of primary cultured porcine granulosa cells have been studied using the whole-cell configuration of the patch-clamp technique. And effects of K+ channel blockers upon progesterone production of the cells have been also studied. The author has identified and characterized two types of K+ currents, transient outward current (Ito) and a delayed rectifier K+ current (Ik), and Ca2+ current (Ica). Ito and Ik were voltage -and calcium-dependent. Both of the currents were blocked by 4-aminopyridine (4-AP), a K+ channel blocker, but only Ik was sensitive to tetraethylammonium (TEA), 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. These findings suggested that the current was T-type Ca2+ current. LH and dibutyryl cAMP, potent stimulants of steroid production, attenuated Ito 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 did not modulate Ca2+ current directly, but it suppressed Ito through cAMP. 4-AP (0.2-5 mM) suppressed basal and LH-induced progesterone production of porcine granulosa cells dose-dependently, but TEA (2-10 mM) did not influence progesterone production. These data suggest that Ito may play a role in steroid secretion or other functions in granulosa cells.
Kusaka
M
M
Department of Obstetrics and Gynecology, Hokkaido University School of Medicine, Sapporo Japan.
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D005260:Female; D006107:Granulosa Cells / Q000378:metabolism / Q000502:physiology*; D007986:Luteinizing Hormone / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects; D011374:Progesterone / Q000096:biosynthesis; D013552:Swine
D015220:Calcium Channels; D015221:Potassium Channels; D011374:Progesterone; D007986:Luteinizing Hormone; D000242:Cyclic AMP