Effects of Ca(2+) influx through nonselective cation channel on noradrenaline-induced mitogenic responses.

We have recently shown that noradrenaline induces extracellular Ca(2+) influx through nonselective cation channel (NSCC) in Chinese hamster ovary cells expressing alpha(1A)-adrenoceptors (CHO-alpha(1A)). Moreover, this NSCC is sensitive to (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) and resistant to 1-[b-(3-[4-Methoxyphenyl]propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride (SK&F 96365). In the present study, we characterized the effects of extracellular Ca(2+) influx through NSCC on noradrenaline-induced mitogenic responses and activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) of CHO-alpha(1A) using LOE 908 and SK&F 96365. Noradrenaline induced a mitogenic response in CHO-alpha(1A). LOE 908 completely inhibited the noradrenaline-induced mitogenesis, whereas SK&F 96365 did not inhibit it. The IC(50) value of LOE 908 for noradrenaline-induced mitogenesis was similar to that for the noradrenaline-induced increase in intracellular free Ca(2+) concentration (Ca(2+)). Noradrenaline stimulated ERK1/2 activity. The magnitude of noradrenaline-induced ERK1/2 activity in the absence of extracellular Ca(2+) was 40% of that in the presence of extracellular Ca(2+). LOE 908 partially (60%) inhibited the noradrenaline-induced ERK1/2 activity, whereas SK&F 96365 did not inhibit it. The IC(50) value of LOE 908 for noradrenaline-induced ERK1/2 activity was similar to that for the noradrenaline-induced increase in Ca(2+). Collectively, these results demonstrate that extracellular Ca(2+) influx through LOE 908-sensitive and SK&F 96365-resistant NSCC may be essential for noradrenaline-induced mitogenesis in CHO-alpha(1A). Moreover, the noradrenaline-induced ERK1/2 activity involves two distinct pathways, one dependent on extracellular Ca(2+) influx through NSCC, whereas the other is independent of the influx.