TRPC1: store-operated channel and more

Transient receptor potential canonical 1 (TRPC1) is a transmembrane protein expressed in a range of vertebrate cells including smooth muscle, endothelium, neurones and salivary gland cells. It functions as an element of a mixed cationic Ca(2+-)permeable channel, probably commonly as part of a heterotetrameric assembly involving other related proteins such as TRPC5. Wide-ranging biological roles of TRPC1 are suggested, including regulation of smooth muscle and stem cell proliferation, endothelin-evoked arterial contraction, salivary gland secretion, endothelial permeability, glutamatergic neurotransmission, growth cone turning, neuroprotection, neuronal differentiation, lipid raft integrity and the nuclear factor of activated T-cell transcription factor. The mechanisms by which TRPC1 serves these functions are starting to emerge. At one level, it is apparent that TRPC1 is subcellularly compartmentalised, at least in part in cholesterol-rich caveolae closely associated with sub-plasmalemmal endoplasmic reticulum. At another level, TRPC1 is embedded in a protein complex that can include inositol trisphosphate receptor, homer, calmodulin, caveolin-1, FKBP25, I-mfa, MxA, GluR1 alpha, bFGFR-1, G(q/11) protein, phospholipase C-beta/gamma, protein kinase C-alpha and RhoA. It is also apparent that TRPC1 responds to general stimuli-not only depletion of intracellular Ca2+ stores, but also receptor activation, and membrane stretch. We are at the early stages of understanding of how these various signals and components integrate to form a functional channel, and this article provides a brief overview of current progress.