Angiotensin II-induced calcium mobilization in oocytes by signal transfer through gap junctions.

Angiotensin II (AII) stimulates rapid increases in the concentration of cytosolic calcium in follicular oocytes from Xenopus laevis. This calcium response was not present in denuded oocytes, indicating that it is mediated by AII receptors on the adherent follicular cells. The endogenous AII receptors differed in their binding properties from mammalian AII receptors expressed on the oocyte surface after injection of rat adrenal messenger RNA. Also, the calcium responses to activation of the amphibian AII receptor, but not the expressed mammalian AII receptor, were blocked reversibly by octanol and intracellular acidification, treatments that inhibit cell coupling through gap junctions. In addition, AII increased the rate of progesterone-induced maturation. Thus, an AII-induced calcium-mobilizing signal is transferred from follicle cells to the oocyte through gap junctions and may play a physiological role in oocyte maturation.