Calmodulin‐ and protein phosphorylation‐independent release of catecholamines from PC‐12 cells

Abstract

Catecholamine secretion from PC‐12 cells can be triggered by agents that increase intracellular Ca²⁺ and is enhanced by phorbol esters and agents that elevate intracellular cAMP concentrations. In mutant PC‐12 cells lacking cAMP‐dependent protein kinase (PK‐A) in which protein kinase C (PK‐C) was down‐regulated, Ca²⁺‐dependent secretion occurred normally but was no longer enhanced by cAMP or phorbol esters. In digitonin‐permeabilized PC‐12 cells that lacked PK‐C and PK‐A, a range of calmodulin (CaM) inhibitors failed to block Ca²⁺‐triggered catecholamine release. Moreover, Mn²⁺, a CaM activator, failed to trigger catecholamine release whereas Ba²⁺, which does not activate CaM, supported secretion. These results indicate that the basic mechanism of stimulus/secretion coupling in PC‐12 cells does not absolutely require a regulated protein phosphorylation‐ or calmodulin‐dependent step.