Evidence for a dihydropyridine-sensitive and conotoxin-insensitive release of noradrenaline and uptake of calcium in adrenal chromaffin cells.
1. It has been suggested that neuronal voltage-sensitive calcium channels (VSCC) may be divided into dihydropyridine (DHP)-sensitive (L) and DHP-insensitive (N and T), and that both the L and the N type channels are attenuated by the peptide blocker omega-conotoxin. Here the effects of omega-conotoxin on release of noradrenaline and uptake of calcium in bovine adrenal chromaffin cells were investigated. 2. Release of noradrenaline in response to 25 mM K+, 65 mM K+, 10 nM bradykinin or 10 microM prostaglandin E1 was not affected by omega-conotoxin in the range 10 nM-1 microM. 3. 45Ca2+ uptake stimulated by high K+ and prostaglandin was attenuated by 1 microM nitrendipine and enhanced by 1 microM Bay K 8644; these calcium fluxes were not modified by 20 nM omega-conotoxin. 4. With superfused rat brain striatal slices in the same medium as the above cell studies, release of dopamine in response to 25 mM K+ was attenuated by 20 nM omega-conotoxin. 5. These results show that in these neurone-like cells, release may be effected by calcium influx through DHP-sensitive but omega-conotoxin-insensitive VSCC, a result inconsistent with the suggestion that omega-conotoxin blocks both L-type and N-type neuronal calcium channels.
Owen
P J
PJ
Department of Pharmacology and Therapeutics, University of Leicester.
Marriott
D B
DB
Boarder
M R
MR
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000527:Alprostadil / Q000378:metabolism; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002417:Cattle; D002838:Chromaffin System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020916:Conotoxins; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D004095:Dihydropyridines / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism; D066298:In Vitro Techniques; D008978:Mollusk Venoms / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology
D002132:Calcium Radioisotopes; D020916:Conotoxins; D004095:Dihydropyridines; D008978:Mollusk Venoms; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C055407:conotoxin GV; D000527:Alprostadil; D011188:Potassium; D002118:Calcium; D004298:Dopamine; D009638:Norepinephrine