The Transient Receptor Potential (TRP) superfamily is one of the largest ion channel families and consists of diverse groups of proteins. In mammals, about 28 genes encode the TRP ion channel subunits. The mammalian TRP superfamily comprises six subfamilies known as the TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPML (mucolipins), TRPP (polycystin) and the TRPA (ANKTM1) ion channels^1-4.

The TRPC subfamily consists of seven proteins named TRPC1 to 7, which can be further divided into four subgroups based on their sequence homology and functional similarities:
1.) TRPC1 2.) TRPC4 and TRPC5 3.) TRPC3, TRPC6, TRPC7 4.) TRPC2^2,5. They are highly expressed in the central nervous system and to a lesser extent in peripheral tissues.

TRPC1 was the first mammalian TRP protein that was reported to form an ion channel². It can co-assemble with other TRPC subunits (TRPC3, TRPC4, TRPC5) to form heterotetramers whose properties are distinct from that of their homomeric form. The existence of the TRPC1 homomers has not been established as yet^1-3.

The TRPC1, TRPC4 and TRPC5 can be activated either by Ca²⁺, store depletion or by GPCR stimulation pathways, while TRPC3, TRPC6 and TRPC7 form non-selective cationic channels that are activated by the stimulation of GPCRs. TRPC1, 4 and TRPC5 are assumed to form components of store operated channels in some cell types such as salivary gland cells, endothelial cells and vascular smooth muscle cells⁶.