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- inositol 1,4,5-trisphosphate-sensitive stores.