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Excitation-driven entry of Ca 2+ through L-type voltage-gated Ca 2+ channels controls gene expression in neurons and a variety of fundamental activities in other kinds of excitable cells. The probability of opening of Ca V 1.2 L-type channels is subject to pronounced enhancement by cAMP-dependent protein kinase (PKA), which is scaffolded to Ca V 1.2 channels by A-kinase anchoring proteins (AKAPs). Ca V 1.2 channels also undergo negative autoregulation via Ca 2+ -dependent inactivation (CDI), which strongly limits Ca 2+ entry. An abundance of evidence indicates that CDI relies upon binding of Ca 2+ /calmodulin (CaM) to an isoleucine–glutamine motif in the carboxy tail of Ca V 1.2 L-type channels, a molecular mechanism seemingly unrelated to phosphorylation-mediated channel enhancement. But our work reveals, in cultured hippocampal neurons and a heterologous expression system, that the Ca 2+ /CaM-activated phosphatase calcineurin (CaN) is scaffolded to Ca V 1.2 channels by the neuronal anchoring protein AKAP79/150, and that overexpression of an AKAP79/150 mutant incapable of binding CaN (ΔPIX; CaN-binding PXIXIT motif deleted) impedes CDI. Interventions that suppress CaN activity—mutation in its catalytic site, antagonism with cyclosporine A or FK506, or intracellular perfusion with a peptide mimicking the sequence of the phosphatase's autoinhibitory domain—interfere with normal CDI. In cultured hippocampal neurons from a ΔPIX knock-in mouse, CDI is absent. Results of experiments with the adenylyl cyclase stimulator forskolin and with the PKA inhibitor PKI suggest that Ca 2+ /CaM-activated CaN promotes CDI by reversing channel enhancement effectuated by kinases such as PKA. Hence, our investigation of AKAP79/150-anchored CaN reconciles the CaM-based model of CDI with an earlier, seemingly contradictory model based on dephosphorylation signaling.
Oliveria et al. (Wed,) studied this question.