Endothelin-1-induced contraction of rat thoracic aorta depends on calcium entry through three types of calcium channel.

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 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1-H-imidazoe l hydrochloride (SK&F 96365) (a blocker of NSCC-2 and SOCC) and (RS)-(3,4-dihydro-6,7-dimethoxyisoquinoline-1-gamma l)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxyphenyl)ethyl]acetamide (LOE 908) (a blocker of NSCC-1 and NSCC-2). For our study we characterized Ca2+ channels involved in ET-1-induced contractions and increases in the intracellular free Ca2+ concentration ([Ca2+]i) using these blockers. Our results show that the response to lower concentrations of ET-1 involves only one Ca2+ channel which is sensitive to SK&F 96365 and LOE 908 (NSCC-2). In contrast, the response to higher concentrations of ET-1 involves two types of Ca2+ channel in addition to NSCC-2: one is sensitive to SK&F 96365 but resistant to LOE 908 (SOCC), and the other is resistant to SK&F 96365 but sensitive to LOE 908 (NSCC-1). Furthermore, the percentage contribution of Ca2+ entry through NSCC-1, NSCC-2 and SOCC is calculated to be 10%, 50-60% and 30-40%, respectively.