Background Cardiomyocytes (CM) utilize Ca2+ not only in excitation-contraction coupling (ECC), but also as a signaling molecule promoting for example cardiac hypertrophy. It is largely unclear how Ca2+ triggers signaling in CM in the presence of the rapid and large Ca2+ fluctuations that occur during ECC. A potential route is store-operated Ca2+ entry (SOCE), a drug-inducible mechanism for Ca2+ signaling that requires stromal interaction molecule 1 (STIM1). SOCE can also be induced in cardiomyocytes, which prompted us to study STIM1-dependent Ca2+-entry with respect to cardiac hypertrophy in vitro and in vivo. Methods and Results Consistent with earlier reports, we found drug-inducible SOCE in neonatal rat cardiomyocytes, which was dependent on STIM1. While this STIM1-dependent, drug-inducible SOCE was only marginal in adult cardiomyocytes isolated from control hearts, it significantly increased in cardiomyocytes isolated from adult rats that had developed compensated cardiac hypertrophy after abdominal aortic banding. Moreover, we detected an inwardly rectifying current in hypertrophic cardiomyocytes that occurs under native conditions (i.e. in the absence of drug-induced store depletion) and is dependent on STIM1. By manipulating its expression, STIM1 was found to be both sufficient and necessary for cardiomyocyte hypertrophy both in vitro and in the adult heart in vivo. Stim1 silencing by AAV9-mediated gene transfer protected rats from pressure overload-induced cardiac hypertrophy. Conclusions STIM1 promotes cardiac hypertrophy by controlling a previously unrecognized sarcolemmal current.

Transient receptor potential canonical (TRPC) Ca 2+ -permeant channels, especially TRPC3, are increasingly implicated in cardiorenal diseases. We studied the possible role of fibroblast TRPC3 in the development of renal fibrosis. In vitro, a macromolecular complex formed by TRPC1/TRPC3/TRPC6 existed in isolated cultured rat renal fibroblasts. However, specific blockade of TRPC3 with the pharmacologic inhibitor pyr3 was sufficient to inhibit both angiotensin II-and 1-oleoyl-2-acetyl-sn-glycerol-induced Ca 2+ entry in these cells, which was detected by fura-2 Ca 2+ imaging. TRPC3 blockade or Ca 2+ removal inhibited fibroblast proliferation and myofibroblast differentiation by suppressing the phosphorylation of extracellular signalregulated kinase (ERK1/2). In addition, pyr3 inhibited fibrosis and inflammation-associated markers in a noncytotoxic manner. Furthermore, TRPC3 knockdown by siRNA confirmed these pharmacologic findings. In adult male Wistar rats or wild-type mice subjected to unilateral ureteral obstruction, TRPC3 expression increased in the fibroblasts of obstructed kidneys and was associated with increased Ca 2+ entry, ERK1/2 phosphorylation, and fibroblast proliferation. Both TRPC3 blockade in rats and TRPC3 knockout in mice inhibited ERK1/2 phosphorylation and fibroblast activation as well as myofibroblast differentiation and extracellular matrix remodeling in obstructed kidneys, thus ameliorating tubulointerstitial damage and renal fibrosis. In conclusion, TRPC3 channels are present in renal fibroblasts and control fibroblast proliferation, differentiation, and activation through Ca 2+ -mediated ERK signaling. TRPC3 channels might constitute important therapeutic targets for improving renal remodeling in kidney disease.