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 synaptosomal protein synapsin Ib without having direct effects on protein kinases or protein phosphatases. DTG dose-dependently decreased the basal cytosolic free Ca2+ concentration ([Ca2+]i) and blocked the depolarization-dependent increases in [Ca2+]i. These effects were inhibited by the sigma antagonists rimcazole and BMY14802. The nitric oxide donors sodium nitroprusside (SNP) and 8-(p-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate decreased basal [Ca2+]i and the KCI-evoked rise in [Ca2+]i to an extent similar to DTG. SNP, but not DTG, 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 45Ca2+ uptake and efflux under basal conditions and inhibited the 45Ca2+ uptake induced by depolarization with KCI. The KCI-evoked rise in [Ca2+]i was inhibited by omega-conotoxin (omega-CgTx)-GVIA and -MVIIC but not nifedipine and omega-agatoxin-IVA. The effect of DTG on decreasing the KCI-evoked rise in [Ca2+]i was additive with omega-CgTx-MVIIC but not with omega-CgTx-GVIA. These data suggest that DTG was producing some of its effects on synapsin I and dynamin phosphorylation and intrasynaptosomal Ca2+ levels via inhibition of N-type Ca2+ channels.
Brent
P J
PJ
Neuroscience Group, Discipline of Clinical Pharmacology, Mater Hospital, Waratah, New South Wales, Australia.
Herd
L
L
Saunders
H
H
Sim
A T
AT
Dunkley
P R
PR
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects; D006152:Cyclic GMP / Q000378:metabolism; D006146:Guanidines / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008024:Ligands; D010750:Phosphoproteins / Q000096:biosynthesis*; D016548:Prosencephalon / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017480:Receptors, sigma / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D006146:Guanidines; D008024:Ligands; D010750:Phosphoproteins; D017480:Receptors, sigma; D006152:Cyclic GMP; C050232:1,3-ditolylguanidine; D002118:Calcium