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 ef fect in single human melanocytes were studied using fura-2/AM. ET-1 in duced a transient increase in [Ca2+](i) in a concentration-dependent m anner, The transient [Ca2+](i) increase was followed by a sustained pl ateau level of [Ca2+](i) which was higher than the initial [Ca2+](i) l evel, IRL-1620, a specific ET-B receptor agonist, increased [Ca2+](i) in a dose-dependent manner, BQ-788, a specific ET-B receptor antagonis t, abolished the ET-1-induced [Ca2+](i) increase. but BQ-123, a specif ic ET-A receptor antagonist, failed to prevent it. U73122, an inhibito r of phospholipase C (PLC), inhibited the ET-1-induced [Ca2+](i) rise in a dose-dependent manner, Prior depletion of intracellular Ca2+ stor es with thapsigargin, an inhibitor of Ca2+-ATPase of the endoplasmic r eticulum, abolished the ET-1-induced Ca2+ transient, whereas removal o f extracellular Ca2+ with EGTA eliminated the sustained rise. These re sults suggest that in cultured human melanocytes the binding of ET-1 t o ET-B receptors and the subsequent activation of PLC mediate ET-1-ind uced [Ca2+](i) increase, The transient [Ca2+](i) increase is attribute d to mobilization of Ca2+ from inositol 1,4,5-trisphosphate-sensitive intracellular Ca2+ stores, and the sustained [Ca2+](i) level may be re lated to the influx of extracellular Ca2+.