REGULATION OF ENDOGENOUS CA2-AMP AND CYCLIC GMP-DEPENDENT PROTEIN-KINASES IN PLEURODELES OOCYTES( CHANNELS BY CYCLIC)

The effects of cyclic AMP (cAMP) and cyclic GMP (cGMP) on dihydropyrid ine sensitive Ca2+ channels were investigated under voltage-clamp in d efolliculated Pleurodeles oocytes. Intracellular injection of cAMP or extracellular application of the permeable cAMP analogue (8-Bromo cAMP , 8Br-cAMP) decreased the Ba current (I,,) This effect on I,a was bloc ked by the injection of protein kinase A inhibitor. Similar results we re found upon internal application of the catalytic subunit of protein kinase A. In contrast, the injection of cGMP or perfusion of 8Br-cGMP increased I-Ba amplitude. The increase of I,a by 8Br-cGMP was blocked by the injection of the selective inhibitor of protein kinase G (KT58 23). These results support the hypothesis that the basal Ba current am plitude 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.