Plasma Membrane Insertion of TRPC5 Channels Contributes to the Cholinergic Plateau Potential in Hippocampal CA1 Pyramidal Neurons

In cultured hippocampal neurons, transient receptor potential 5 (TRPC5) channels are translocated and inserted into plasma membranes of hippocampal neurons to generate nonselective cation (NSC) currents. We investigated whether TRPC5 channel translocation also contributes to the generation of NSC currents underlying the afterdepolarizations and plateau potentials (PPs) in hippocampal pyramidal cells that are induced by muscarinic receptor activation. Using a biotinylation assay to quantify the change in surface membrane proteins in acute hippocampal slices, we found that muscarinic stimulation significantly enhanced the levels of TRPC5 protein on the membrane surface but not those of TRPC1 or TRPC4 channels. We then investigated the pharmacological sensitivity of the cation current observed during muscarinic stimulation to determine if a component could be due to TRPC5 channels. The TRPC channel antagonists 2-APB and SKF96365 strongly depressed the generation of PPs, the underlying tail currents (I-tail) and the associated dendritic Ca2+ influx induced by muscarinic receptor activation in pyramidal neurons. High intracellular concentrations of ATP, which specifically inhibit TRPC5 channels, depressed Itail. In addition, pretreatment with the calmodulin (CaM) inhibitor W-7, which depresses recombinant TRPC5 currents, inhibited both the cation current (I-tail) and the surface insertion of TRPC5 channels. Finally, the phosphatidylinositide 3-kinase (PI3K) inhibitor wortmannin, which blocks translocation of TRPC5 channels in cell culture, also inhibited both the Itail and the surface insertion of TRPC5 channels. Therefore, we conclude that insertion of TRPC5 channels contributes to the generation of the prolonged afterdepolarizations following muscarinic stimulation. This altered plasma membrane expression of TRPC5 channels in pyramidal neurons may play an important role in the generation of prolonged neuronal depolarization and bursting during the epileptiform seizure discharges of epilepsy. (C) 2010 Wiley-Liss, Inc.