Proteinase-activated receptor agonists stimulate the increase in intracellular Ca2+ in cardiomyocytes and proliferation of cardiac fibroblasts from chick embryos

We studied activation of cultured cardiomyocytes and cardiac fibroblasts from chick embryos induced by agonists of PAR1 (thrombin and PAR1 peptide agonist) and PAR2 (trypsin, factor Xa, and peptide SLIGRL) by analyzing changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) and cardiac fibroblast proliferation. Exposure of cardiomyocytes with thrombin induced immediate permanent dose-dependent increase in [Ca(2+)](i). Ca(2+) response decreased in a calcium-free medium. Peptide agonists of PAR1 and PAR2 also stimulated the increase in [Ca(2+)](i) in cardiomyocytes. Thrombin induced a short-term increase in [Ca(2+)](i) in cardiac fibroblasts and potentiated cell proliferation. PAR2 agonists trypsin and peptide SLIGRL stimulated proliferation of cardiac fibroblasts. Our results indicate that cardiomyocytes and cardiac fibroblasts from chick embryos have at least two types of PAR (types 1 and 2).