In N-type Ca²⁺ channels, the mechanism of inactivation - decline of inward current during a depolarizing voltage step- is still controversial between voltage-dependent inactivation and Ca²⁺-dependent inactivation. In the previous paper we demonstrated that fast component of inactivation of N-type calcium channels does not involve classic Ca²⁺-dependent mechanism and the slowly inactivating component could result from a Ca²⁺-dependent process. However, there should be signal transduction pathway which enhances inactivation no matter what the inactivation mechanism is. We have investigated the effect of phosphorylation on calcium channels of rat sympathetic neurons. Intracellular dialysis with the phosphatase inhibitors okadaic acid markedly enhanced the inactivation. The rapidly inactivating component is N-type calcium current, which is blocked by ՙ-conotoxin GVIA. Staurosporine, a nonselective protein kinase inhibitor, prevented the action of okadaic acid, suggesting that protein phosphorylation is involved. More specifically lavendustin C, inhibitor of CaM kinase II, prevented the action of okadaic acid, suggesting that calmodulin dependent pathway is involved in inactivation process. It is not certain to this point whether phosphorylation process is inactivation itself. Molecular biological research regarding binding site should be followed to address the question of how the divalent cation binding site is related to phoshorylation process.

KeywordsN-type Ca²⁺ channels, Inactivation, Voltage-dependent, Ca²⁺-dependent, Phosphorylation, Binding site