Further characterization of phasic calcium influx in rat cerebrocortical synaptosomes: inferences regarding calcium channel type(s) in nerve endings.
Under conditions minimizing the contribution of Na+/Ca2+ exchange to calcium entry in synaptosomes, the K+ depolarization-dependent calcium influx (JCa) is a single exponential function of time. JCa activates and slowly inactivates at membrane potentials positive to -50 mV, a result indicating the involvement of moderate voltage-activating, slowly inactivating calcium channels. Calcium channels in synaptosomes are characterized by stronger sensitivity to blockage by Cd2+ than Co2+, insensitivity to dihydropyridine calcium antagonists or the agonist Bay K 8644, and weak, partial sensitivity to the peptide toxin omega-conotoxin GVIA. These characteristics suggest that voltage-sensitive calcium channels in rat cerebrocortical synaptosomes are dissimilar from the somatic T, N, or L channel types. JCa is not affected by treatment of synaptosomes with the adenylate cyclase activator forskolin, the membrane permeant dibutyryl-cyclic AMP, or the kinase C activator phorbol 12-myristate 13-acetate diester, results suggesting that calcium channels in synaptosomes are not directly modulated by protein kinase A- or C-mediated phosphorylation.
Suszkiw
J B
JB
Department of Physiology and Biophysics, University of Cincinnati College of Medicine, Ohio.
Murawsky
M M
MM
Shi
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000145:classification* / Q000187:drug effects / Q000502:physiology; D002540:Cerebral Cortex / Q000378:metabolism* / Q000648:ultrastructure; D004594:Electrophysiology; D007700:Kinetics; D008978:Mollusk Venoms / Q000494:pharmacology; D009411:Nerve Endings / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism*; D020866:omega-Conotoxin GVIA
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008978:Mollusk Venoms; D020866:omega-Conotoxin GVIA; D002118:Calcium