GoProtein Does Not Regulate ATP-Stimulated [Ca2+]iElevation or Noradrenaline Release in PC12 Cells

The roles of Go, a heterotrimeric GTP binding (G) protein with a 40-kDa α subunit and which is localized predominantly in neuronal cells, in exocytosis have been discussed recently. PC12 pheochromocytoma cell line is a convenient model in which to study the Ca2+-dependent mechanisms of the neurosecretory process. The stimulation of ATP receptors or addition of KCl stimulated an elevation of cytosolic free Ca2+concentration ([Ca2+]i) and [3H]noradrenaline (NA) release in PC12 cells. In this study, we investigated the roles of Goin ATP- and KCl-stimulated reactions. Nerve growth factor treatment for 2 days and transfection of PC12 cells with cDNA of subunit of Go(Goα) had no effect on ATP-stimulated [3H]NA release, although both treatments increased levels of the Goαand its trimeric form by about twofold over those in unstimulated cells. The [Ca2+]irise induced by ATP in NGF-treated cells was similar to that in control cells, although the maximal response was slightly smaller. Cholera toxin treatment for 2 days inhibited ATP- and KCl-stimulated NA release, although this treatment caused an approximately twofold increase in the level of Go. Pertussis toxin treatment, which ADP ribosylated over 90% of endogenous G proteins such as Go, had no effect on ATP-stimulated reactions. These findings show that Godoes not directly regulate ATP-stimulated Ca2+channels or the NA release process in PC12 cells. Cholera toxin-sensitive protein(s) may regulate exocytosis.