Abstract-Sustained elevation in the intracellular Ca 2ϩ concentration via Ca 2ϩ influx, which is activated by a variety of mechanisms, plays a central regulatory role for cardiovascular functions. Recent molecular biological research has disclosed an unexpectedly diverse array of Ca 2ϩ -entry channel molecules involved in this Ca 2ϩ influx. These include more than ten transient receptor potential (TRP) superfamily members such as TRPC1, TRPC3-6, TRPV1, TRPV2, TRPV4, TRPM4, TRPM7, and polycystin (TRPP2). Most of them appear to be multimodally activated or modulated and show relevant features to both acute hemodynamic control and long-term remodeling of the cardiovascular system, and many of them have been found to respond not only to receptor stimulation but also to various forms of stimuli. There is good evidence to implicate TRPC1 in neointimal hyperplasia after vascular injury via store-depletion-operated Ca 2ϩ entry. TRPC6 likely contributes to receptor-operated and mechanosensitive Ca 2ϩ mobilizations, being involved in vasoconstrictor and myogenic responses and pulmonary arterial proliferation and its associated disease (idiopathic pulmonary arterial hypertension). Considerable evidence has also been accumulated for unique involvement of TRPV1 in blood flow/pressure regulation via sensory vasoactive neuropeptide release. New lines of evidence suggest that TRPV2 may act as a Ca 2ϩ -overloading pathway associated with dystrophic cardiomyopathy, TRPV4 as a mediator of endothelium-dependent hyperpolarization, TRPM7 as a proproliferative vascular Mg 2ϩ entry channel, and TRPP2 as a Ca

Abstract.We investigated the possible involvement of the melastatin family protein TRPM7 in Ca 2+-mediated proliferative control of human retinoblastoma (RB) cells. , LOE908, 2-APB) suppressed the spontaneous Ca 2+ influx and decelerated the growth of RB cells with similar efficacies. Excision of the RB cell membrane (inside-out) into MgATP-free solution induced a 70pS single channel activity, which was effectively inhibited by millimolar concentrations of Mg 2+ or MgATP. RT-PCR and immunocytochemical experiments revealed the expression of TRPM7 mRNA and protein in RB cells, and heterologous expression of TRPM7 in HEK293 cells reproduced the key features of I spont . In contrast, elimination of this protein from RB cells by siRNA silencing markedly reduced I spont density and the magnitude of spontaneous Ca 2+ influx, which was paralleled by decreased TRPM7 immunoreactivity, decelerated cell proliferation, and retarded G 1 / S cell cycle progression. These results suggest a significant regulatory role of TRPM7 for RB cell proliferation as a spontaneously activated Ca 2+ influx pathway.

Abstract-TRPC6 is a non-voltage-gated Ca 2ϩ entry/depolarization channel associated with vascular tone regulation and remodeling. Expressed TRPC6 channel responds to both neurohormonal and mechanical stimuli, the mechanism for which remains controversial. In this study, we examined the possible interactions of receptor and mechanical stimulations in activating this channel using the patch clamp technique. In HEK293 cells expressing TRPC6, application of mechanical stimuli (hypotonicity, shear, 2,4,6-trinitrophenol) caused, albeit not effective by themselves, a prominent potentiation of cationic currents (I TRPC6 ) induced by a muscarinic receptor agonist carbachol. This effect was insensitive to a tarantula toxin GsMTx-4 (5 mol/L). A similar extent of mechanical potentiation was observed after activation of I TRPC6 by GTP␥S or a diacylglycerol analog 1-oleoyl-2-acetylsn-glycerol (OAG). Single TRPC6 channel activity evoked by carbachol was also enhanced by a negative pressure added in the patch pipette. Mechanical potentiation of carbachol-or OAG-induced I TRPC6 was abolished by small interfering RNA knockdown of cytosolic phospholipase A 2 or pharmacological inhibition of -hydroxylation of arachidonic acid into 20-HETE (20-hydroxyeicosatetraenoic acid). Conversely, direct application of 20-HETE enhanced both OAG-induced macroscopic and single channel TRPC6 currents. Essentially the same results were obtained for TRPC6-like cation channel in A7r5 myocytes, where its activation by noradrenaline or Arg8 vasopressin was greatly enhanced by mechanical stimuli via 20-HETE production. Furthermore, myogenic response of pressurized mesenteric artery was significantly enhanced by weak receptor stimulation dependently on 20-HETE production. These results collectively suggest that simultaneous operation of receptor and mechanical stimulations may synergistically amplify transmembrane Ca 2ϩ mobilization through TRPC6 activation, thereby enhancing the vascular tone via phospholipase C/diacylglycerol and phospholipase A 2 /-hydroxylase/20-HETE pathways. (Circ Res. 2009;104:1399-1409.) Key Words: mechanotransduction Ⅲ G q/11 protein-coupled receptor Ⅲ Ca 2ϩ entry channel I t has widely been recognized that cellular functions are elaborately controlled by both neurohormonal activities and mechanical stresses. 1,2 For example, in the cardiovascular system, the contractile status of arteries is not only regulated by autonomic nerve activities, circulating vasoactive hormones, and paracrinely released autacoids but is also greatly influenced by mechanical stresses such as blood flow and pressure. [3][4][5] These 2 mechanisms are expected to operate simultaneously in vivo, but little is known about how they could interact mutually.A member of the canonical transient receptor potential (TRP) protein family TRPC6 (the sixth canonical subfamily member of TRP protein) is ubiquitously expressed in vascular smooth muscle cells (VSMCs) and implicated in the regulation of vascular tone and remodeling. 6 Like many other TRP isoforms, activat...