Gonadotropins, Prostaglandin F_2α 및 Ouabain이 황체막의 Ca⁺⁺}-ATPase 활성도에 미치는 영향

Effects of Gonadotropins, Prostaglandin F_2α, and Ouabain on the Ca⁺⁺}-ATPase Activity in Luteal Membranes

It has been reported that the luteal function may be regulated by the intracellular Ca⁺⁺ level which may be adjusted partially by the high affinity Ca⁺⁺-ATPase in luteal cell membranes. Then, one may expect that luteotropic and/or luteolytic agents, such as gonadotropins, prostaglandin F_2α (PGF_2α) and ouabain, affect the intracellular Ca⁺⁺ level. In this present study, therefore, we examined the effects of luteinizing hormone (LH, or human chorionic gonadotropin, hCG), PGF^2α and ouabain on the kinetic properties of the high affinity Ca⁺⁺-ATPase in light membrane, heavy membrane, and microsomal fractions from the highly luteinized ovary. LH (or hCG) increased the affinity and the Vmax for Ca⁺⁺ both in light membrane and heavy membrane. PGF^2α increased the Vmax in light membrane and decreased the Km in heavy membrane for Ca⁺⁺ at low concentration (5 μg/ml). At higher concentration, however, PGF^2α oppositly affected on kinetic properties, that shown at low concentration. Ouabain, a potent inhibitor of Na⁺-K⁺-ATPase, increased the Km at high concentration (10^-4 M), however, decreased the Vmax for Ca⁺⁺ in light membrane at low concentration (10^-6 M). Also, ouabain increased the Km for Ca⁺⁺ in heavy membrane without changes in the Vmax at both concentrations. It seems that LH and low dose of PGF^2α increase the intracellular Ca⁺⁺ level and cause in activation of Ca⁺⁺-ATPase, however, higher dose of PGF^2α and ouabain inhibit directly Ca⁺⁺-ATPase activity and result in increase in intracellular Ca⁺⁺ level. According to the above results, we suggest that luteotropic and/or luteolytic agents regulate the luteal progesterone (P₄) production through two different pathways; one is cyclic adenosine monophosphate (cAMP)-dependent and another is Ca⁺⁺-dependent. Intracellula. Ca⁺⁺ level regulated by the high affinity Ca⁺⁺-ATPase may affect both pathways in a time-dependent fashion. LH (or hCG) acts on the luteal P₄ production via both pathways. The initial step is Ca⁺⁺ dependent, and the late step is cAMP dependent. PGF^2α and ouabain increase the intracellular Ca⁺⁺ concentration so that basal luteal P₄ production is increased and LH-stimulated P₄ production is inhibited by the inhibiting LH-dependent adenylate cyclase activity.