Ionic Channels Formed by TRPC4.

TRPC4 (transient receptor potential canonical 4) is a member of the TRPC subfamily and, within this sub-family, TRPC4 is most closely related to TRPC5. A number of splice variants of TRPC4 have been identified, whereby TRPC4α and TRPC4β appear to be the most abundant isoforms in various species. TRPC4α comprises six transmembrane segments and the N- and C-termini are located intracellularly. Additionally, TRPC4α shares other structural features with members of the TRPC sub-group, including ankyrin-like repeats, coiled-coil regions and binding sites for calmodulin and IP3 receptors. Three calmodulin-binding domains have been identified in the C-terminus of TRPC4α. TRPC4β lack 84 amino acids in the C-terminus, which correspond to the last two calmodulin-binding sites of TRPCα. The first and last calmodulin-binding domains of TRPC4α overlap with binding sites for the N- and C-termini of IP3 receptors. The ionic channels formed by TRPC4 appear to be Ca2+-permeable, although there is a considerably discrepancy in the degree of Ca2+ selectivity. Studies with mice lacking TRPC4 (TRPC4−/−) suggest an important role for TRPC4 in supporting Ca2+ entry. The defect in Ca2+ entry in TRPC4−/− mice appears to be associated with a reduction of the vasorelaxation of arteries, vascular permeability in the lung and neurotransmitter release from thalamic dendrites. [ABSTRACT FROM AUTHOR]