Cyclic AMP-dependent modulation of cardiac Ca channels expressed in Xenopus laevis oocytes.

Cyclic AMP-dependent modulation of cardiac L-type voltage-dependent Ca channel (VDCC) has been probed in Xenopus laevis oocytes injected with poly(A+) RNA from rat heart. A 2 to 3 fold increase of the Ba current amplitude was routinely obtained upon microinjection of cAMP (50-500 microM). Inhibition of protein kinase A (PKA) dramatically reduced the Ba current amplitude, indicating that cAMP-dependent modulation plays an important role in maintaining the basal activity of expressed Ca channels. Moreover, the effects of the DHP agonist Bay K 8644 on kinetic properties of expressed Ba current (IBa,C) were dependent on PKA activation. The results suggest that most expressed cardiac L-type VDCCs are phosphorylated and demonstrate that reconstitution in Xenopus oocytes is a suitable approach to address how phosphorylation regulates VDCC activity.