Endothelin-1 increases intracellular Ca2+ in rabbit pulmonary artery smooth muscle cells through phospholipase C

In freshly isolated rabbit pulmonary artery smooth muscle cells, endothelin (ET)-1 induced a transient increase in intracellular Ca2+ concentration ([Ca2+](i)) followed by a return to the initial [Ca2+](i). This response was not abolished by the voltage-dependent Ca2+ channel blocker nicardipine or removal of Ca2+ from the bath solution but was inhibited by ryanodine and thapsigargin. This finding suggested that the increase in [Ca2+](i) induced by ET-1 was attributable to release of Ca2+ from ryanodine- and inositol 1,4,5-trisphosphate-sensitive intracellular Ca2+ stores. The transient increase in [Ca2+](i) induced by ET-1 was also inhibited by pretreatment with antagonists of ET type A and B (ETA and ETB) receptors (BQ-123 and BQ-788, respectively). Furthermore, the ETB receptor agonist IRL-1620 induced an increase in [Ca2+](i) that was followed by a sustained increase in [Ca2+](i); the sustained increase in [Ca2+](i) was blocked by nicardipine. Using the nystatin-perforated patch-clamp technique, we found that IRL-1620 caused an increase in Ca2+ current that was inhibited by addition of ET-1. ET-1 did not inhibit Ca2+ current when cells were pretreated with BQ-123. These results suggested that when both receptor types are activated, the opposing responses lead to abolition of the sustained [Ca2+](i) increases induced by ETB receptor activation. Western blot analysis confirmed expression of ETA and ETB receptors. Finally, U-73122 inhibited the ET-1-induced [Ca2+](i) increase, indicating that phospholipase C was involved in modulation of the ET-1-induced [Ca2+](i) increase in rabbit pulmonary artery smooth muscle cells.