Mobilization of intracellular Ca2+ by endothelin-1 in rat intrapulmonary arterial smooth muscle cells

Endothelin-1 (ET-1) increases intracellular Ca2+ concentration ([Ca2+]i) in pulmonary arterial smooth muscle cells (PASMCs); however, the mechanisms for Ca2+ mobilization are not clear. We determined the contributions of extracellular influx and intracellular release to the ET-1-induced Ca2+ response using Indo 1 fluorescence and electrophysiological techniques. Application of ET-1 (10−10 to 10−8 M) to transiently (24–48 h) cultured rat PASMCs caused concentration-dependent increases in [Ca2+]i. At 10−8 M, ET-1 caused a large, transient increase in [Ca2+]i (>1 μM) followed by a sustained elevation in [Ca2+]i(<200 nM). The ET-1-induced increase in [Ca2+]i was attenuated (<80%) by extracellular Ca2+ removal; by verapamil, a voltage-gated Ca2+-channel antagonist; and by ryanodine, an inhibitor of Ca2+ release from caffeine-sensitive stores. Depleting intracellular stores with thapsigargin abolished the peak in [Ca2+]i, but the sustained phase was unaffected. Simultaneously measuring membrane potential and [Ca2+]i indicated that depolarization preceded the rise in [Ca2+]i. These results suggest that ET-1 initiates depolarization in PASMCs, leading to Ca2+influx through voltage-gated Ca2+ channels and Ca2+ release from ryanodine- and inositol 1,4,5-trisphosphate-sensitive stores.