Cardiac calcium channels expressed in Xenopus oocytes are modulated by dephosphorylation but not by cAMP-dependent phosphorylation.

摘要: Enhancement of cardiac L-type Ca2+ channel activity by norepinephrine via phosphorylation protein kinase A (PKA) underlines the positive inotropic effect this transmitter and is a classical example an ion modulation. However, it not clear whether itself (and which subunit) substrate for PKA. We have expressed various combinations subunits in Xenopus oocytes injecting subunit mR-NAs. Expression beta or alpha 2/delta + potentiated native (endogenous) currents oocyte (similar to T N but L-type). This endogenous current was enhanced intracellular injection cAMP catalytic PKA, reversed PKA inhibitor suggesting presence basal phosphatase activity. When 1 beta, composition at levels high enough that contribution became negligible, failed increase current, whereas inhibitors reduced amplitude current. Reduction observed regardless subunit, major role process. These results suggest that, like heart, when oocytes, channels are phosphorylated state dephosphorylation reduces their unlike situation cannot be PKA-catalyzed phosphorylation, already fully its state.