Studies on the endothelin-1-induced contraction of rat granulation tissue pouch mediated by myofibroblasts

摘要

A granulation tissue pouch, mostly composed of myofibroblasts, was prepared by injecting rats subcutaneously with croton oil. The contraction of the granulation tissue pouch caused by endothelin-1 (ET-1) and the effects of the ET receptor antagonists, BQ123 and BQ788 on it were thus examined. ET-1 produced contractions in a dose-dependent manner. Pretreatment with BQ123, an ET_A receptor selective antagonist, shifted the dose-response curve to the right, whereas pretreatment with BQ788, an ET_B receptor selective antagonist, showed little effect. IRL1620, an ET_B receptor selective agonist, did not cause any contraction in the granulation tissue pouch. The existence of both ET_A and ET_B receptors in the granulation tissue pouch and in cultured myofibroblasts was demonstrated by RT-PCR. Intracellular Ca~(2+) mobilization in Fura-2/acetyl-methoxy ester loaded cultured myofibroblasts isolated from the granulation tissue was also examined. ET-1 produced a transient increase in [Ca~(2+)]_i followed by a sustained elevation of [Ca~(2+)]_i, whereas IRL1620 caused only a transient peak. These results suggest that the ET-1 induced contraction of granulation tissue is mainly mediated through the mobilization of Ca~(2+) from the extracellular space caused by stimulation with ET_A receptor.