Reduction of the same calcium current component by A and C kinases: differential pertussis toxin sensitivity.

Voltage-clamp techniques were used to study the effect of forskolin, 8-Br-cyclic AMP, and phorbol 12,13-dibutyrate (PDBu) on the 3 voltage-dependent calcium current components of mouse dorsal root ganglion neurons in culture. Forskolin and 8-Br-cyclic AMP selectively reduced the transient high-threshold (N-type) calcium current component, an effect also produced by PDBu, a C kinase activator. Pretreatment of cultures with pertussis toxin prevented the reduction of calcium current by PDBu, but was without effect on the reductions produced by forskolin or 8-Br-cyclic AMP. These results support the contention that activation of both A and C kinases selectively affect calcium currents in vertebrate neurons by reducing the N-type calcium current component. While the activation of the C kinase required a G protein to exert its effect, the activation of A kinase did not.