Endothelin-B receptor-mediated Ca²⁺ signaling in human melanocytes

Abstract

 The mechanism of an endothelin-1- (ET-1-) induced intracellular Ca²⁺ ([Ca²⁺]_i) increase and the receptor subtype(s) responsible for this effect in single human melanocytes were studied using fura-2/AM. ET-1 induced a transient increase in [Ca²⁺]_i in a concentration-dependent manner. The transient [Ca²⁺]_i increase was followed by a sustained plateau level of [Ca²⁺]_i which was higher than the initial [Ca²⁺]_i level. IRL-1620, a specific ET-B receptor agonist, increased [Ca²⁺]_i in a dose-dependent manner. BQ-788, a specific ET-B receptor antagonist, abolished the ET-1-induced [Ca²⁺]_i increase, but BQ-123, a specific ET-A receptor antagonist, failed to prevent it. U73122, an inhibitor of phospholipase C (PLC), inhibited the ET-1-induced [Ca²⁺]_i rise in a dose-dependent manner. Prior depletion of intracellular Ca²⁺ stores with thapsigargin, an inhibitor of Ca²⁺-ATPase of the endoplasmic reticulum, abolished the ET-1-induced Ca²⁺ transient, whereas removal of extracellular Ca²⁺ with EGTA eliminated the sustained rise. These results suggest that in cultured human melanocytes the binding of ET-1 to ET-B receptors and the subsequent activation of PLC mediate ET-1-induced [Ca²⁺]_i increase. The transient [Ca²⁺]_i increase is attributed to mobilization of Ca²⁺ from inositol 1,4,5-trisphosphate-sensitive intracellular Ca²⁺ stores, and the sustained [Ca²⁺]_i level may be related to the influx of extracellular Ca²⁺.