RESUMEN
Our laboratory has evidence that multiple nicotinic acetylcholine receptor subtypes regulate bovine adrenal catecholamine release. In the following studies, receptor protection assays were used to differentiate adrenal nicotinic receptor subpopulations. Under alkylating conditions, bromoacetylcholine (30 microM) reduced nicotinic receptor-stimulated adrenal catecholamine secretion by approximately 80%. When 100 microM tubocurarine was present during alkylation, nicotine-stimulated secretion was reduced by less than 30%. Hexamethonium (500 microM), decamethonium (500 microM), mecamylamine (50 microM), pentolinium (50 microM), adiphenine (50 microM), methyllycaconitine (1 microM) and alpha-bungarotoxin (1 microM) afforded no protection when present during alkylation. When the pharmacology of residual, tubocurarine-protected receptors was investigated, the EC50 value for nicotine's stimulatory effects on secretion significantly increased from 4.0 (2.5-6.5) microM in control cells to 9.1 (7.2-11.4) microM in tubocurarine-protected cells. In addition, the IC50 value for tubocurarine's inhibitory effects on release significantly decreased from 0.7 (0.5-0.9) microM in control cells to 0.3 (0.2-0.4) microM in tubocurarine-protected cells. These studies support the use of protection assays to characterize nicotinic receptor subpopulations.
Asunto(s)
Médula Suprarrenal/metabolismo , Células Cromafines/metabolismo , Neuronas/metabolismo , Antagonistas Nicotínicos/farmacología , Receptores Nicotínicos/metabolismo , Tubocurarina/farmacología , Acetilcolina/farmacología , Médula Suprarrenal/efectos de los fármacos , Alquilación/efectos de los fármacos , Animales , Unión Competitiva/efectos de los fármacos , Unión Competitiva/fisiología , Catecolaminas/metabolismo , Bovinos , Células Cultivadas , Células Cromafines/efectos de los fármacos , Interacciones Farmacológicas/fisiología , Neuronas/efectos de los fármacos , Receptores Nicotínicos/efectos de los fármacosRESUMEN
The importance of disulfide bridges in muscle nicotinic receptors is well established; however, for neuronal nicotinic receptors, the effects of sulfhydryl modification are less definitive. In these studies the effects of treatment with the mild reducing agent, dithiothreitol, on adrenal nicotinic receptors are described. We have found that following dithiothreitol treatment, adrenal chromaffin cells retained the ability to be stimulated by a variety of nicotinic receptor agonists including nicotine, acetylcholine, cytisine, epibatidine, and bromoacetylcholine. However, with dithiothreitol treatment, changes in apparent affinities were seen with two agonists, epibatidine and bromoacetylcholine. These effects of dithiothreitol on apparent affinities were concentration-dependent and reversible upon treatment with an oxidizing agent. Dithiothreitol treatment also produced effects on secretion that were independent of nicotinic receptor activation. Our results are unlike those in other tissues containing nicotinic receptors and suggest that subunit composition of nicotinic receptors influences the functional outcome of sulfhydryl modification.
Asunto(s)
Glándulas Suprarrenales/metabolismo , Disulfuros/metabolismo , Receptores Nicotínicos/metabolismo , Compuestos de Sulfhidrilo/química , Glándulas Suprarrenales/efectos de los fármacos , Animales , Catecolaminas/metabolismo , Bovinos , Células Cromafines/efectos de los fármacos , Células Cromafines/metabolismo , Ditiotreitol/farmacología , Agonistas Nicotínicos/farmacología , Antagonistas Nicotínicos/farmacología , Receptores Nicotínicos/química , Receptores Nicotínicos/efectos de los fármacos , Reactivos de Sulfhidrilo/farmacologíaRESUMEN
We have prepared ring E analogs of the diterpenoid alkaloid methyllycaconitine. These compounds have been assayed for nicotinic activity and were found to act as functional antagonists on adrenal nicotinic receptors.