Evidence for a dihydropyridine-sensitive and conotoxin-insensitive release of noradrenaline and uptake of calcium in adrenal chromaffin cells

OWEN, P J and MARRIOTT, D B and BOARDER, M R (1989) Evidence for a dihydropyridine-sensitive and conotoxin-insensitive release of noradrenaline and uptake of calcium in adrenal chromaffin cells. British Journal of Pharmacology, 97 (1). pp. 133-138. ISSN 0007-1188

Abstract

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 ω-conotoxin. Here the effects of ω-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 μm prostaglandin E1 was not affected by ω-conotoxin in the range 10 nm-1 μm. 3 45Ca2+ uptake stimulated by high K+ and prostaglandin was attenuated by 1 μm nitrendipine and enhanced by 1 μm Bay K 8644; these calcium fluxes were not modified by 20 nm ω-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 ω-conotoxin. 5 These results show that in these neurone-like cells, release may be effected by calcium influx through DHP-sensitive but ω-conotoxin-insensitive VSCC, a result inconsistent with the suggestion that ω-conotoxin blocks both L-type and N-type neuronal calcium channels.