Journal Article

\Slow\ Voltage-Dependent Inactivation of CaV2.2 Calcium Channels Is Modulated by the PKC Activator Phorbol 12-Myristate 13-Acetate (PMA): e0134117

Zhu, Lei, Currie, Kevin PM, McDavid, Sarah

2015

Overview

CaV2.2 (N-type) voltage-gated calcium channels (Ca2+ channels) play key roles in neurons and neuroendocrine cells including the control of cellular excitability, neurotransmitter / hormone secretion, and gene expression. Calcium entry is precisely controlled by channel gating properties including multiple forms of inactivation. \"Fast\" voltage-dependent inactivation is relatively well-characterized and occurs over the tens-to- hundreds of milliseconds timeframe. Superimposed on this is the molecularly distinct, but poorly understood process of \"slow\" voltage-dependent inactivation, which develops / recovers over seconds-to-minutes. Protein kinases can modulate \"slow\" inactivation of sodium channels, but little is known about if/how second messengers control \"slow\" inactivation of Ca2+ channels. We investigated this using recombinant CaV2.2 channels expressed in HEK293 cells and native CaV2 channels endogenously expressed in adrenal chromaffin cells. The PKC activator phorbol 12-myristate 13-acetate (PMA) dramatically prolonged recovery from \"slow\" inactivation, but an inactive control (4 alpha -PMA) had no effect. This effect of PMA was prevented by calphostin C, which targets the C1-domain on PKC, but only partially reduced by inhibitors that target the catalytic domain of PKC. The subtype of the channel beta -subunit altered the kinetics of inactivation but not the magnitude of slowing produced by PMA. Intracellular GDP- beta -S reduced the effect of PMA suggesting a role for G proteins in modulating \"slow\" inactivation. We postulate that the kinetics of recovery from \"slow\" inactivation could provide a molecular memory of recent cellular activity and help control CaV2 channel availability, electrical excitability, and neurotransmission in the seconds-to-minutes timeframe.