Characterization of calcium signaling pathways in human cardiac fibroblast

Abstract

Introduction: Ca2+ signals play an important role in the physiological activities of many types of cells. Though cardiac fibroblasts play an essential role in the maintenance of extracellular matrix in the normal heart and as mediators of inflammatory and fibrotic myocardial remodelling in the injured and failing heart, Ca2+ signaling pathways in human cardiac fibroblast (HCF) are poorly understood. The present study aims to characterize Ca2+ signaling pathways in HCFs. Methods: Intracellular Ca2+ activity was determined using a confocal microscopy and gene expression was examined with RT-PCR. Results: [Ca2+]i oscillations were present in 30% of cells and were dependent on Ca2+ entry. The oscillatory frequency was reduced by the voltage-operated Ca2+ channel (VOCC) blocker Nifedipine and Ca2+ oscillations were abolished by the store-operated Ca2+ entry (SOCE) channel blocker La3+. The PLC inhibitor U-73122 and the InsP3R inhibitor 2-APB, but not RyR blocker ryanodine, abolished the Ca2+ oscillations, while InsP3R agonist thimerosal enhanced Ca2+ oscillations. RT-PCR revealed molecular identities of Ca2+ signal pathways, including mRNAs for InsP3R1-3, SERCA1-3, L-type Ca2+ channels and the store-operated Ca2+ channel-related genes including TRPC1, 3, 4, 6 were significant, but not mRNAs for ryanodine receptor in HCFs. Conclusion: Our results firstly demonstrate that spontaneous Ca2+ oscillations are present in cultured HCFs, and [Ca2+]i mobilization in HCF is likely mediated by both SOCE and VOCCs and mobilized by InsP3 via PLC activation. Mechanisms of the spontaneous Ca2+ oscillations and role of them in cellular physiology remain to be studied in HCF.