Receptor-mediated Regulation of the Nonselective Cation Channels TRPC4 and TRPC5

Mammalian transient receptor potential channels (TRPCs) form a family of Ca2+-permeable cation channels currently consisting of seven members, TRPC1–TRPC7. These channels have been proposed to be molecular correlates for capacitative Ca2+ entry channels. There are only a few studies on the regulation and properties of the subfamily consisting of TRPC4 and TRPC5, and there are contradictory reports concerning the possible role of intracellular Ca2+ store depletion in channel activation. We therefore investigated the regulatory and biophysical properties of murine TRPC4 and TRPC5 (mTRPC4/5) heterologously expressed in human embryonic kidney cells. Activation of Gq/11-coupled receptors or receptor tyrosine kinases induced Mn2+ entry in fura-2-loaded mTRPC4/5-expressing cells. Accordingly, in whole-cell recordings, stimulation of Gq/11-coupled receptors evoked large, nonselective cation currents, an effect mimicked by infusion of guanosine 5′-3-O-(thio)triphosphate (GTPγS). However, depletion of intracellular Ca2+ stores failed to activate mTRPC4/5. In inside-out patches, single channels with conductances of 42 and 66 picosiemens at −60 mV for mTRPC4 and mTRPC5, respectively, were stimulated by GTPγS in a membrane-confined manner. Thus, mTRPC4 and mTRPC5 form nonselective cation channels that integrate signaling pathways from G-protein-coupled receptors and receptor tyrosine kinases independently of store depletion. Furthermore, the biophysical properties of mTRPC4/5 are inconsistent with those ofICRAC, the most extensively characterized store-operated current.