Pharmacological heterogeneity among calcium channels that subserve acetylcholine release in vertebrate forebrain.
Inhibition of calcium-evoked [3H]ACh release by different classes of calcium channel blockers was compared among calcium-naive synaptosomes from chick, frog and rat forebrain tissues. In all three species, [3H]ACh release was insensitive to nifedipine (0.03-3 microM) but was completely inhibited by cadmium (IC50 range = 0.7-1.7 microM) or cobalt (190-350 microM). In contrast, the peptide omega-conotoxin revealed marked species heterogeneity in that [3H]ACh release was potently blocked in chick and rat synaptosomes (IC50 congruent to 1 nM), whereas frog tissue was notably resistant (IC50 greater than 100 nM). Together, these data provide functional evidence for pharmacological heterogeneity among presynaptic calcium channels that subserve [3H]ACh release.
Vickroy
T W
TW
Department of Physiological Sciences, University of Florida, Gainesville 32610.
Schneider
C J
CJ
Hildreth
J M
JM
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002645:Chickens; D005089:Exocytosis / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D010456:Peptides, Cyclic / Q000494:pharmacology; D016548:Prosencephalon / Q000187:drug effects / Q000378:metabolism*; D011894:Rana pipiens; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010456:Peptides, Cyclic; D020960:omega-Conotoxins; C053423:Conus magus toxin; D000109:Acetylcholine