Interaction between Calcineurin and Ca ²⁺ /Calmodulin Kinase-II in Modulating Cellular Functions

Abstract

Roles of calcineurin (CaN), a Ca ²⁺/calmodulin- (CaM-) dependent protein phosphatase, and Ca ²⁺/CaM-dependent protein kinase-II (CaMKII) in modulating K ⁺ channel activity and the intracellular Ca ²⁺ concentration ([Ca ²⁺] _i) have been investigated in renal tubule epithelial cells. The channel current through the cell membrane was recorded with the patch-clamp technique, and [Ca ²⁺] _i was monitored using fura-2 imaging. We found that a CaN-inhibitor, cyclosporin A (CyA), lowered the K ⁺ channel activity and elevated [Ca ²⁺] _i, suggesting that CyA closes K ⁺ channels and opens Ca ²⁺-release channels of the cytosolic Ca ²⁺-store. Moreover, both of these responses were blocked by KN-62, an inhibitor of CaMKII. It is suggested that the CyA-mediated response results from the activation of CaMKII. Indeed, Western blot analysis revealed that CyA increased phospho-CaMKII, an active form of CaMKII. These findings suggest that CaN-dependent dephosphorylation inhibits CaMKII-mediated phosphorylation, and the inhibition of CaN increases phospho-CaMKII, which results in the stimulation of CaMKII-dependent cellular actions.