Pharmacological properties of calcium entry channels in A7r5 cells activated by endothelin-1

Using whole-cell recordings of patch-clamp and monitoring of the intracellu lar free calcium (Ca2+) concentration ([Ca2+]i), we characterized Ca2+ entr y channels in A7r5 cells activated by endothelin-1 (ET-1). ET-1 activates t hree types of voltage-independent Ca2+ entry channels: two types of Ca2+-pe rmeable nonselective cation channels (designated NSCC-1 and NSCC-2) and sto re-operated Ca2+ channel (SOCC). Furthermore, it was found that these chann els can be discriminated pharmacologically using Ca2+ channel blockers such as 1-{beta-[3-(4-methoxyphenyl)propoxyl]-4-methoxyphenyl}-1-H-imidazoel hy drochloride (SK&F 96365) and (RS)-(3,4-dihydro-6,7-dimethoxyisoquinoline-1- gamma1)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxyphenyl)ethyl] acetamide (LOE 90 8). NSCC-1 is resistant to SK&F 96365 but sensitive to LOE908, whereas NSCC -2 is sensitive to both drugs: SOCC is sensitive to SK&F 96365 but resistan t to LOE 908. Using these channel blockers, we analyzed the Ca2+ entry chan nels involved in the ET-1-induced increase in [Ca2+]i of the cells. The inc rease induced by lower concentrations of ET-1 (less than or equal to 0.1 nM ) was unaffected by SK&F 96365 but it was abolished by LOE 908. In contrast , the increase caused by higher concentrations of ET-1 (greater than or equ al to 1 nM) was suppressed by SK&F 96365 or LOE 908 to about 35% of control s, and abolished by combined treatment with SK&F 96365 and LOE 908. These r esults show that the increase in [Ca2+] resulting from lower concentrations of ET-1 (less than or equal to0.1 nM) involves Ca2+ entry through only NSC C-1, whereas that resulting from higher concentrations of ET-1 involves Ca2 + entry through NSCC-1, NSCC-2 and SOCC, contributing 35%, 30% and 30%, res pectively, to total Ca2+ entry.