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-DIETHYLAMINOETHYLDIPHENYLPROPYLACETATE (SKF 5254)
1 Department of Pharmacology and Therapeutics, University of Manitoba Faculty of Medicine, Winnipeg, Canada
Exposure of rabbit aortic strips to SKF 525A (2.6 x 10-5 M; 1 x 10-5 g/ml) for 30 minutes blocked potassium-induced contractions without reducing those to moderate concentrations of norepinephrine or phenylephrine. Contractions induced by calcium in aortic strips incubated in a calcium-free, high-potassium solution were almost completely abolished by a 15-minute exposure to SKF 525A. Responses to norepinephrine and phenylephrine were decreased only partially and very slowly during exposure to SKF 525A. Responses induced by calcium added in the presence of norepinephrine in a calcium-free medium were significantly, but only partially, depressed by a 15-minute exposure to SKF 525A. It was concluded that SKF 525A selectively blocks some step in the process by which potassium-induced depolarization promotes the movement of extracellular and/or superficially bound calcium to the contractile elements, but does not directly interfere with mobilization of calcium by norepinephrine from a separate, firmly bound source. The results obtained are also consonant with a combined parallel and series arrangement of calcium binding sites, i.e., that extracellular calcium can reach the firmly bound fraction both via superficial binding sites (antagonized by SKF 525A) and by an independent mechanism. The effects of SKF 525A on responses to 5-hydroxytryptamine, histamine and angiotensin indicated that these stimulants utilize superficial and firmly bound calcium to differing extents in producing contractions of aortic strips. The apparent specificity of the observed effects of SKF 525A suggests that this drug may be a useful tool in studies of the involvement of extracellular and loosely bound calcium in various processes.
Submitted on January 8, 1970
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