Stimulation of recombinant Ca(v)3.2, T-type, Ca(2+) channel currents by CaMKIIgamma(C)

Molecular cloning of low-voltage activated (LVA) T-type calcium channels has enabled the study of their regulation in heterologous expression systems. Here we investigate the regulation of Ca(v)3.2 alpha(1)-subunits (alpha1H) by calcium- and/or calmodulin-dependent protein kinase II (CaMKII). 293 cells stably expressing alpha1H were transiently transfected with CaMKIIgamma(C). Using the whole-cell recording configuration, we observed that elevation of pipette free Ca(2+) (1 microM) in the presence of CaM (2 microM) increases T-type channel activity selectively at negative potentials, evoking an 11 mV hyperpolarizing shift in the half-maximal potential (V(1/2)) for activation. The V(1/2) of channel inactivation is not altered by Ca(2+)/CaM. These effects reproduced modulation observed in adrenal zona glomerulosa cells. The potentiation by Ca(2+)/CaM was dependent on the co-expression of CaMKIIgamma(C) and required Ca(2+)/CaM-dependent kinase activity. Peptide (AIP) and lipophilic (KN-62) protein kinase inhibitors prevented the Ca(2+)/CaM-induced changes in channel gating without altering basal Ca(v)3.2 channel activity (27 nM free Ca(2+)) as did replacing pipette ATP with adenylyl imidodiphosphate (AMP-PNP), a non-hydrolysable analogue. CaMKII-dependent potentiation of channel opening resulted in significant increases in apparent steady-state open probability (P(o)) and sustained channel current at negative voltages. Under identical conditions, CaMKII activation did not regulate the activity of Ca(v)3.1 channels, the first cloned member (alpha1G) of the T-type Ca(2+) channel family. Our results provide the first evidence for the differential regulation of two members of the Ca(v)3 family by protein kinase activation and the first report reconstituting CaMKII-dependent regulation of any cloned Ca(2+) channel.