Advances in modern cell biology and physiological techniques have dramatically improved our understanding of basic cellular functions. Together with classical genetic and biochemical approaches, these technical advances have allowed us to uncover the novel functions of a variety of proteins inside the cell. For example, recent studies have revealed intracellular functions of several TRP proteins (reviewed in Ref. 1), a family of cation non-selective ion channels that were initially thought to operate exclusively at the plasma membrane to regulate the transmembrane flux of Na+, K+, Ca2+, and Mg2+. Initially discovered in the Drosophila melanogaster photoreceptor, TRPs are also found in vertebrates, widely expressed in most tissues and cell types.2 The TRP superfamily can be divided into six subfamilies: canonical (TRPC), vanilloid (TRPV), melastatin (TRPM), polycystin (TRPP), mucolipin (TRPML), and ankyrin transmembrane proteins (TRPA). Currently, the most well-defined TRP functions are serving as cellular sensors for detecting an array of environmental stimuli including temperature, mechanical forces, and pain. However, the list of nonsensory functions for TRPs also has expanded rapidly in recent years.
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