Pharmacological characterization of Ca2+ entry channels in endothelin-1-induced contraction of rat aorta using LOE 908 and SKandF 96365

Abstract

1. We have recently shown that endothelin-1 (ET-1) activates two types of Ca2+-permeable nonselective cation channels (designated NSCC-1 and NSCC-2) and store-operated Ca2+ channel (SOCC). These channels can be pharmacologically discriminated using Ca2+ channel blockers such as SKandF 96365 and LOE 908. Here we characterized Ca2+ entry channels involved in ET-1-induced contractions of rat thoracic aortic rings and increases in the intracellular free Ca2+ concentration ([Ca2+](i)) of single smooth muscle cells using these blockers. 2. LOE 908 or a blocker of voltage-operated Ca2+ channel nifedipine had no effect on the contractions and increases in [Ca2+](i) induced by thapsigargin or ionomycin, whereas SKandF 96365 abolished them. 3. The contractions and increases in [Ca2+](i) induced by ET-1 depended on extracellular Ca2+ but were resistant to nifedipine. The responses to lower concentrations (≤ 0.1 nM) of ET-1 were abolished by either SKandF 96365 or LOE 908. The responses to higher concentrations (≥ 1 nM) were abolished by SKandF 96365, but were partially resistant to LOE 908. 4. SKandF 96365 inhibited the LOE 908-resistant contractions induced by higher concentrations of ET-1 with IC50 values similar to those for contractions induced by thapsigargin or ionomycin. 5. These results show that the contractions and increases in [Ca2+](i) of rat aortic smooth muscles at lower concentrations of ET-1 involve only one Ca2+ entry channel which is sensitive to SKandF 96365 and LOE 908 (NSCC-2), whereas those at higher concentrations of ET-1 involve another Ca2+ entry channel which is sensitive to SKandF 96365 but resistant to LOE 908 (SOCC) in addition to the former channel.