Transient receptor potential channels, the kidney and hypertension

Smooth muscle cells as well as non-excitable cells express multiple cationic channels with significant permeability to calcium, potassium and sodium. Several of these channels are sensors of calcium store depletion, G-protein coupled receptor activation, membrane stretch, intracellular Ca2+, pH, oxidative stress, phospholipid signals and other factors. A novel family of such channels is encoded by genes homologues of Drosophila TRP (transient receptor potential). Direct evidence exists for roles of TRPC1, TRPC4/5, TRPC6, TRPV2, TRPP1 and TRPP2 in store-operated Ca2+- gating and epithelial cell Ca2+ transport, thus controlling smooth muscle reactivity and at the same time renal homeostasis of divalent cations. Mice deficient in TRPV5 express phenotypic defects amongst which hypercalciuria and impaired bone mineral density. Polycystin 2 (PC2), encoded by the PKD2 gene, is an epithelial transmembrane protein whose mutation is associated to autosomal dominant polycystic kidney disease (ADPKD). PC2 behaves as a TRP-type Ca2+-permeable nonselective cation channel. It is implicated in the transient increase in cytosolic Ca2+ in renal epithelial cells, and may be linked to the activation of subsequent signaling pathways. Recent studies indicate that a PC1-PC2 channel complex is an obligatory novel signaling pathway implicated in the transduction of environmental signals into cellular events. TRP-related ion channels may thus play a role in the pathogenesis of hypertension through direct effects on vascular smooth muscle contraction, renal perfusion/hemodynamics, and the total body balance of divalent cations.