Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

Rationale: Orai1 and the associated calcium release-activated calcium (CRAC) channel were discovered in the immune system. Existence also in endothelial cells has been suggested, but the relevance to endothelial biology is mostly unknown.Objective: The aim of this study was to investigate the relevance of Orai1 and CRAC channels to vascular endothelial growth factor (VEGF) and endothelial tube formation. Methods and Results:

Mammalian homologues of Drosophila melanogaster transient receptor potential (TRP) are a large family of multimeric cation channels that act, or putatively act, as sensors of one or more chemical factor1,2. Major research objectives are the identification of endogenous activators and the determination of cellular and tissue functions of these novel channels. Here we show activation of TRPC5 homomultimeric and TRPC5-TRPC1 heteromultimeric channels3-5 by extracellular reduced thioredoxin acting by breaking a disulphide bridge in the predicted extracellular loop adjacent to the ion-selectivity filter of TRPC5. Thioredoxin is an endogenous redox protein with established intracellular functions, but it is also secreted and its extracellular targets are largely unknown6-9. Particularly high extracellular concentrations of thioredoxin are apparent in rheumatoid arthritis8,10-12, an inflammatory joint disease disabling millions of people worldwide13. We show that TRPC5 and TRPC1 are expressed in secretory fibroblast-like synoviocytes from patients with rheumatoid arthritis, endogenous TRPC5-TRPC1 channels of the cells are activated by reduced thioredoxin, and blockade of the channels enhances secretory activity and prevents suppression of secretion by thioredoxin. The data suggest a novel ion channel activation mechanism that couples extracellular thioredoxin to cell function.Striking activators of TRPC5 are extracellular lanthanide ions4,14,15. Effects of these ions depend on a glutamic acid residue at position 54314 in the predicted extracellular loop adjacent to the ion pore (Supplementary Fig. 1-2). This structural feature may, therefore, have functional importance in enabling extracellular factors to activate the channels. Because lanthanides are unlikely physiological activators we were interested in alternatives and developed a hypothesis based on amino acid sequence alignment which showed two cysteine residues near glutamic acid 543 that are conserved in TRPC5, TRPC4 and TRPC1 ( Supplementary Fig. 2), a subset of the seven TRPC channels1-5. TRPC5 and TRPC4 have similar functional properties4 and both form heteromultimers with TRPC13-5, a subunit that has weak targeting to the plasma membrane when expressed in isolation3,16. Pairs of cysteine residues may be covalently linked by a disulphide bridge that can be cleaved by reduction. We therefore applied the chemical reducing agent dithiothreitol (DTT) to HEK 293 cells expressing TRPC515,16. There was channel activation with the characteristic current-voltage relationship (I-V) of TRPC5 and block by 2-APB, an inhibitor of TRPC55 (Fig. 1a, b, d). Current recovered on wash-out of DTT (data not shown). Similarly, the membrane-impermeable disulphide reducing agent TCEP (Fig. 1c, d) activated TRPC5, whereas the thiol reagent MTSET had no effect (Fig. 1d). TRPC5 was inhibited by cadmium ions only after pre-treatment with DTT ( Fig. 1e, f), consistent with the metal ion acting by re-engaging cysteines17. Other TRP channels lacking the cysteine pair in a similar po...

Abstract-In a screen of potential lipid regulators of transient receptor potential (TRP) channels, we identified sphingosine-1-phosphate (S1P) as an activator of TRPC5. We explored the relevance to vascular biology because S1P is a key cardiovascular signaling molecule. TRPC5 is expressed in smooth muscle cells of human vein along with TRPC1, which forms a complex with TRPC5. Importantly, S1P also activates the TRPC5-TRPC1 heteromultimeric channel. Because TRPC channels are linked to neuronal growth cone extension, we considered a related concept for smooth muscle. We find S1P stimulates smooth muscle cell motility, and that this is inhibited by E3-targeted anti-TRPC5 antibody. Ion permeation involving TRPC5 is crucial because S1P-evoked motility is also suppressed by the channel blocker 2-aminoethoxydiphenyl borate or a TRPC5 ion-pore mutant. S1P acts on TRPC5 via two mechanisms, one extracellular and one intracellular, consistent with its bipolar signaling functions. The extracellular effect appears to have a primary role in S1P-evoked cell motility. The data suggest S1P sensing by TRPC5 calcium channel is a mechanism contributing to vascular smooth muscle adaptation. Key Words: vascular smooth muscle Ⅲ vein Ⅲ sphingosine-1-phosphate Ⅲ transient receptor potential Ⅲ calcium channel S phingosine-1-phosphate (S1P) has emerged as a major endogenous signaling phospholipid with diverse roles in yeast, plants, and mammals. 1 Proposed functions include the regulation of cell proliferation, migration, programmed death, and pathological processes including cancer, asthma, inflammation, and trauma. There has been particular interest in the role of S1P in the cardiovascular system, where it accumulates in atherosclerotic lesions and plays a role in ischemic preconditioning of the heart. 2-5 S1P is derived from the phosphorylation of sphingosine catalyzed by sphingosine kinase, sphingosine being from ceramide and ceramide from sphingomyelin, a constituent lipid of signaling microdomains of plasma membrane lipid rafts and caveolae. 3 S1P is detected in serum at almost 1 mol/L, although protein binding impacts on the available concentration and local concentrations may vary substantially. 6 S1P is quite unusual among signaling molecules in having separate intracellular and extracellular effects. 1,4,7,8 It affects vascular smooth muscle cell migration, 9,10 evokes contraction of rat mesenteric artery, 11 and slows pacemaker activity of the sino-atrial node of the heart. 12 The underlying mechanisms are only partially worked out, but vascular smooth muscle cells respond to S1P with transient followed by sustained elevation of the cytosolic Ca 2ϩ concentration, 10,11,13,14 whereas cardiac myocytes show activation of potassium current and S1P-evoked "Ca 2ϩ deregulation," depending on extracellular Ca 2ϩ . 12,15 Despite positive effects on Ca 2ϩ signaling, the molecular basis of a Ca 2ϩ channel stimulated by S1P is unknown. L-type voltage-gated Ca 2ϩ channels are inhibited by S1P. 12 The Drosophila transient receptor potential ...