Subunit composition of mammalian transient receptor potential channels in living cells

Hormones, neurotransmitters, and growth factors give rise to calcium entry via receptor-activated cation channels that are activated downstream of phospholipase C activity. Members of the transient receptor potential channel (TRPC) family have been characterized as molecular substrates mediating receptor-activated cation influx. TRPC channels are assumed to be composed of multiple TRPC proteins. However, the cellular principles governing the assembly of TRPC proteins into homo- or heteromeric ion channels still remain elusive. By pursuing four independent experimental approaches—i.e., subcellular cotrafficking of TRPC subunits, differential functional suppression by dominant-negative subunits, fluorescence resonance energy transfer between labeled TRPC subunits, and coimmunoprecipitation—we investigate the combinatorial rules of TRPC assembly. Our data show that ( i ) TRPC2 does not interact with any known TRPC protein and ( ii ) TRPC1 has the ability to form channel complexes together with TRPC4 and TRPC5. ( iii ) All other TRPCs exclusively assemble into homo- or heterotetramers within the confines of TRPC subfamilies—e.g., TRPC4/5 or TRPC3/6/7. The principles of TRPC channel formation offer the conceptual framework to assess the physiological role of distinct TRPC proteins in living cells.