Multiple Ca 2+ signaling pathways regulate intracellular Ca 2+ activity in human cardiac fibroblasts

Ca 2+ signaling pathways are well studied in cardiac myocytes, but not in cardiac fibroblasts. The aim of the present study is to characterize Ca 2+ signaling pathways in cultured human cardiac fibroblasts using confocal scanning microscope and RT‐PCR techniques. It was found that spontaneous intracellular Ca 2+ (Ca   i 2+ ) oscillations were present in about 29% of human cardiac fibroblasts, and the number of cells with Ca   i 2+oscillations was increased to 57.3% by application of 3% fetal bovine serum. Ca   i 2+oscillations were dependent on Ca 2+ entry. Ca   i 2+oscillations were abolished by the store‐operated Ca 2+ (SOC) entry channel blocker La 3+ , the phospholipase C inhibitor U‐73122, and the inositol trisphosphate receptors (IP3Rs) inhibitor 2‐aminoethoxydiphenyl borate, but not by ryanodine. The IP3R agonist thimerosal enhanced Ca   i 2+oscillations. Inhibition of plasma membrane Ca 2+ pump (PMCA) and Na + –Ca 2+ exchanger (NCX) also suppressed Ca   i 2+oscillations. In addition, the frequency of Ca   i 2+oscillations was reduced by nifedipine, and increased by Bay K8644 in cells with spontaneous Ca 2+ oscillations. RT‐PCR revealed that mRNAs for IP3R1‐3, SERCA1‐3, Ca V 1.2, NCX3, PMCA1,3,4, TRPC1,3,4,6, STIM1, and Orai1‐3, were readily detectable, but not RyRs. Our results demonstrate for the first time that spontaneous Ca   i 2+oscillations are present in cultured human cardiac fibroblasts and are regulated by multiple Ca 2+ pathways, which are not identical to those of the well‐studied contractile cardiomyocytes. This study provides a base for future investigations into how Ca 2+ signals regulate biological activity in human cardiac fibroblasts and cardiac remodeling under pathological conditions. J. Cell. Physiol. 223: 68–75, 2010. © 2009 Wiley‐Liss, Inc.