Regulation of endogenous Ca2+ channels by cyclic AMP and cyclic GMP-dependent protein kinases in Pleurodeles oocytes.

The effects of cyclic AMP (cAMP) and cyclic GMP (cGMP) on dihydropyridine sensitive Ca2+ channels were investigated under voltage-clamp in defolliculated Pleurodeles oocytes. Intracellular injection of cAMP or extracellular application of the permeable cAMP analogue (8-Bromo cAMP, 8Br-cAMP) decreased the Ba current (IBa). This effect on IBa was blocked by the injection of protein kinase A inhibitor. Similar results were found upon internal application of the catalytic subunit of protein kinase A. In contrast, the injection of cGMP or perfusion of 8Br-cGMP increased IBa amplitude. The increase of IBa by 8Br-cGMP was blocked by the injection of the selective inhibitor of protein kinase G (KT5823). These results support the hypothesis that the basal Ba current amplitude of Pleurodeles oocytes is under the control of Protein Kinases A (PKA) and G (PKG) activity. This regulation of Ca2+ channels by the second messengers, and particularly by cAMP may reflect an important step in the maturation processus of Pleurodeles oocytes.