TRPC1 store-operated cationic channel subunit.

TRPC1 is a membrane protein that is highly conserved in mammals, amphibians and birds. It is widely expressed in cells throughout the body including in the heart and nervous system. Amino acid sequence analysis and over-expression studies indicate it is an ion channel that allows the transmembrane flux of small cations including sodium and calcium. In some cell types it is apparent that at least a fraction of TRPC1 exists in the plasma membrane. Inhibition of TRPC1 expression or block by TRPC1-specific antibody leads to attenuation of the plasma membrane calcium influx that occurs in response to depletion of calcium levels in sarcoplasmic or endoplasmic reticulum. TRPC1 would, therefore, seem to be a key subunit of store-operated channels (SOCs). TRPC1 is, nevertheless, unlikely to act alone. There is good evidence that it can heteromultimerise with the related proteins TRPC4, TRPC5 and polycystin-2; a tetrameric arrangement is envisaged, but not demonstrated. Like its relative in Drosophila, TRPC1 looks likely to function in a signalplex, a protein complex including inositol 1,4,5-triphosphate (IP(3)) receptor, plasma membrane calcium-ATPase, caveolin-1 and calmodulin. Its localisation in membranes is punctate and associated with functionally discrete calcium signals. TRPC1's function may not only be linked to SOCs but also to other cellular events including the nuclear translocation of the NFAT transcription factor. There is still much to be learned about this fundamental protein.