Cyclic AMP facilitates slow-inactivating Ca2+ channel currents expressed by Xenopus oocyte after injection of rat brain mRNA.

Properties of voltage-sensitive Ca2+ channels expressed in the Xenopus oocyte after injection of rat brain mRNA were investigated using the whole-cell voltage-clamp method as depolarization-induced Ba2+ current, IBa. The apparent decay profile of IBa was considered to be the sum of a transient current (tau approximately 0.4 s) and a more sustained current (tau approximately 4 s). The sustained component was isolated by a weak depolarization from -20 to 0 mV, only detected in the mRNA-injected cells, and rather sensitive to omega-conotoxin GVIA. Moreover, increases in cytosolic cyclic AMP caused potentiation of the long-lasting current. These results suggest that slow-inactivating states of transplanted Ca2+ channels are preferentially modulated by cyclic AMP-dependent protein kinase.