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

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 Ca²⁺ 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 [Ca²⁺](i) followed by a sustained elevation of [Ca²⁺](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 Ca²⁺ from the extracellular space caused by stimulation with ET(A) receptor. Copyright (C) 1998 Elsevier Science B.V.