Ca2+/calmodulin kinase is activated by the phosphatidylinositol signaling pathway and becomes Ca2(+)-independent in PC12 cells.

Hormonal activation of the phosphatidylinositol (PI) signaling system initiates a biochemical pathway that bifurcates to increase cellular levels of diacylglycerol and of inositol trisphosphate/Ca2+. Both Diacylglycerol and Ca2+ are known to activate protein kinase C, a primary mediator of the PI signaling system. We now find that the two limbs of the PI pathway utilize distinct multifunctional protein kinases to mediate their cellular effects. An important consequence of Ca2+ elevated by the PI signaling system, when PC12 cells are treated with bradykinin, is the activation of multifunctional Ca2+/calmodulin-dependent protein kinase. This activation stimulates autophosphorylation of CaM kinase at its regulatory domain and converts it to an active, Ca2(+)-independent species that may be a basis for potentiation of Ca2+ transients.