PROTEIN-PHOSPHORYLATION AND CALCIUM-UPTAKE INTO RAT FOREBRAIN SYNAPTOSOMES - MODULATION BY THE SIGMA-LIGAND, 1,3-DITOLYLGUANIDINE

The sigma ligand 1,3-di-O-tolylguanidine (DTG) increased basal dynamin and decreased depolarization-stimulated phosphorylation of the synapt osomal protein synapsin Ib without having direct effects on protein ki nases or protein phosphatases. DTG dose-dependently decreased the basa l cytosolic free Ca2+ concentration ([Ca2+](i)) and blocked the depola rization-dependent increases in [Ca2+](i). These effects were inhibite d by the sigma antagonists rimcazole and BMY14802. The nitric oxide do nors sodium nitroprusside (SNP) and 8-(p-chlorophenylthio) guanosine-3 ',5'-cyclic monophosphorothioate decreased basal [Ca2+](i) and the KCl -evoked rise in [Ca2+](i) to an extent similar to DTG. SNP, but not DT G, produced a rise in cyclic GMP levels, suggesting that the effect of DTG on [Ca2+](i) was not mediated via downstream regulation of cyclic GMP levels. DTG increased Ca-45(2+) uptake and efflux under basal con ditions and inhibited the Ca-45(2+) uptake induced by depolarization w ith KCI. The KCl-evoked rise in [Ca2+](i) was inhibited by omega-conot oxin (omega-CgTx)-GVIA and -MVIIC but not nifedipine and omega-agatoxi n-IVA. The effect of DTG on decreasing the KCl-evoked rise in [Ca2+](i ) was additive with omega-CgTx-MVIIC but not with omega-CgTx-GVIA. The se data suggest that DTG was producing some of its effects on synapsin I and dynamin phosphorylation and intrasynaptosomal Ca2+ levels via i nhibition of N-type Ca2+ channels.