Current understanding of mammalian TRP homologues.

Calcium influx into the cell from the extracellular medium is crucial for important processes including muscle contraction, secretion and gene expression. This calcium influx is mainly mediated through calcium influx channels, which on the basis of their activation mechanism can be subdivided in voltage-gated calcium channels, which have already been thoroughly characterized and non-voltage-gated calcium permeable channels. This latter group includes ion channels activated by binding of extra and intracellular messengers, mechanical stress or depletion of intracellular calcium stores. Currently little molecular data is available concerning this class of calcium influx channels. However, recent studies have indicated that members of the transient receptor potential (TRP) family of ion channels can function as calcium influx channels both in excitable and non-excitable tissues. On the basis of structural information the TRP family is subdivided in three main subfamilies: the TRPC (canonical) group, the TRPV (vanilloid) group and the TRPM (melastatin) group. The cloning and characterization of members of this cation channel family has exploded during recent years, leading to a plethora of data concerning TRPs in a variety of tissues and species, including mammals, insects and yeast. This review summarizes the currently available information concerning members of the TRP family expressed in mammalian tissues.