Differential Regulation of P/Q and L-Type Voltage Gated Calcium Channels by Lipid Rafts in PC12 Cells

The subcellular localization of ion channels is necessary for their functioning. We have investigated the localization of voltage gated calcium channels (VGCCs), an important class of transmembrane proteins implicated in various cell functions, with lipid rafts in PC12 cells. We demonstrate through immunocytochemical studies, that L-type and P/Q-type VGCCs colocalize with the raft marker Thy-1 and hence, localize in lipid rafts. Whereas N-type VGCCs does not. Functional association of VGCC subtypes with rafts was elucidated by disrupting rafts, through cholesterol depletion using methyl

β

cyclodextrin. Cholesterol depletion enhanced the depolarization induced activity of L-type VGCCs whereas activity of P/Q type channels was inhibited. Also, we observed enhancement of calcium influx with L-type channel specific agonist Bay K 8644 in cholesterol depleted cells as compared to the control. N-type VGCCs did not show functional association with lipid rafts. Raft mediated regulation of L-type VGCC was studied, which indicates that the channels are not activated by change in the membrane potential. Reduction of compartmentalization of SNAP-25 in the low density membrane domains upon cholesterol depletion indicated the possibility of activation of L-type VGCCs through the exocytotic protein SNAP-25.