Molecular mechanisms for the activation of Ca 2+-permeable nonselective cation channels by endothelin-1 in C6 glioma cells

Abstract

We recently demonstrated that endothelin-1 (ET-1) activates two types of Ca 2+-permeable nonselective cation channels (NSCC-1 and NSCC-2) in C6 glioma cells. It is possible to discriminate between these channels by using the Ca 2+ channel blockers SK&F 96365 (1-[β-(3-[4-methoxyphenyl]propoxy)-4-methoxyphenethyl]-1 H-imidazole hydrochloride) and LOE 908 [( R, S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl- N, N-di-[2-(2,3,4-trimethoxyphenyl)ethyl]-acetamide]. LOE 908 is a blocker for NSCC-1 and NSCC-2, whereas SK&F 96365 is an inhibitor for NSCC-2. The purpose of the present study was to identify the G-proteins that are involved in ET-1-activated Ca 2+ channels in C6 glioma cells. ET-1 activated only NSCC-1 in C6 glioma cells preincubated with U73122 (1-[6-[((17β)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1 H-pyrrole-2,5-dione), a phospholipase C (PLC) inhibitor. Microinjection of the dominant negative mutant of G 12/G 13 (G 12G228A/G 13G225A) abolished activation of NSCC-1 and NSCC-2. In contrast, pertussis toxin did not affect any of the Ca 2+ channels in the ET-1-stimulated C6 glioma cells. These results indicate that G 12/G 13 may couple with endothelin receptors and play an important role in the activation of NSCCs in C6 glioma cells. Moreover, the activation mechanisms of NSCC-1 and NSCC-2 by ET-1 were different. NSCC-1 activation depended upon a G 12/G 13-dependent cascade, whereas NSCC-2 activation depended upon both G q/PLC- and G 12/G 13-dependent cascades.