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

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+.