Sources of calcium and the involvement of calmodulin during steroidogenesis and oocyte maturation in follicles ofRana pipiens

✍ Scribed by Francisco, Susan Kleis-San ;Schuetz, Allen W.

• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 845 KB
• Volume: 244
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402440116

✦ Synopsis

In the amphibian ovarian follicle, progesterone production is thought to induce maturation of the enclosed oocyte. Intracellular mechanisms regulating these events in the somatic and germ cells are incompletely understood. However, calcium appears to play a role in the production and action of progesterone. Experiments using calcium antagonists were carried out to delineate the role of extra-and intracellular calcium during in vitro stimulation of follicular steroidogenesis and oocyte maturation. Calcium-free medium, verapamil, and La3+ were used to block Ca2+ influx and inhibited follicular progesterone accumulation in response to frog pituitary homogenate (FPW or exogenous cAMP + IBMX. Progesterone accumulation was not impaired under identical conditions when pregnenolone was added to cultured follicles. TMBS, a n inhibitor of intracellular Ca2+ mobilization, partially inhibited progesterone levels stimulated by FPH at low doses but not higher doses of the inhibitor. However, TMB-8 inhibited FPH-induced oocyte germinal vesicle breakdown (GVBD) in a dose-dependent manner, as well as maturation due to exogenous progesterone or La3 + . Calmodulin antagonists, W-7, R24571, and trifluoperazine, were used to assess the involvement of calmodulin in the responses of these two cell types. All three antagonists inhibited progesterone accumulation induced by FPH with the apparent order of potency being R24571 > W-7 > TFP. W-7 inhibited CAMP-induced progesterone elevation, but had