Dual regulation of R-type CaV2.3 current by Gq-coupled receptors

Abstract

Many high voltage-activated Ca2+ channels are modulated by Gq-coupled M1 muscarinic acetylcholine receptors. CaV2.3 currents are known to be increased by M1 receptor activation, and the increase in the CaV2.3 currents is mediated by phosphorylation of CaV2.3 channel via the activation of protein kinase C (PKC). Here, we report that M1 muscarinic receptors can also inhibit CaV2.3 currents when the channels are fully activated by PKC. In the whole-cell configuration of tsA201 cells, phorbol 12-myristate 13-acetate (PMA), a PKC activator, potentiated CaV2.3 currents by ~ 2-fold. We found that after the PMA-induced potentiation of CaV2.3 currents, application of the M1 receptor agonist oxotremorine-M (Oxo-M), decreased the currents by 52%. We examined if the hydrolysis of plasma membrane phosphoinositides (PIs) were involved in the muscarinic suppression of CaV2.3 currents. We used two methods to deplete PI(4,5)P2; voltage-sensing phosphatase (VSP), and rapamycin-induced translocatable pseudojanin (PJ) system. Activation of VSP suppressed CaV2.3 current by 38%. PJ system could directly dephosphorylate 4- and 5-phosphates from both PI(4)P and PI(4,5)P2 the plasma membrane. After the addition of rapamycin CaV2.3 currents were dramatically and irreversibly decreased by 66% compared to the initial level. Taken together, our results suggest that CaV2.3 currents are modulated by M1 receptor in a dual mode; potentiation by PKC activation and suppression by poly-PI depletion. Activation of M1 receptors can solely decrease CaV2.3 currents in the PKC-activated cells. PJ-induced inhibition of CaV2.3 currents demonstrates that poly-PIs are important in the maintenance of CaV2.3 channel activity. ⓒ 2015 DGIST