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Comparison of the effluxes of 42K+ and 86Rb+ elicited by cromakalim (BRL 34915) in tonic and phasic vascular tissue
Authors:U Quast  Y Baumlin
Institution:(1) Cardiovascular Department, Preclinical Research, Sandoz Ltd, CH-4002 Basel, Switzerland
Abstract:Summary The cromakalim-induced effluxes of 42K+ and 86Rb+ were compared in rat aortic segments and in guinea-pig portal vein. In both vessels, low concentrations of cromakalim (0.1 mgrM) increased the permeability to 86Rb+ 3–4 times less than that to 42K+; at 10 mgrM the difference was about a factor of 1.3–2. In rat aorta, the threshold concentration of cromakalim for 42K+ efflux was ge0.03 mgrM; with 86Rb+ as the tracer ion it was 0.1 mgrM. At similar concentrations, cromakalim relaxed the tension of aortic segments precontracted with 23 mM KCl (IC50 = 0.06 ± 0.01 mgrM). However, no concomitant increase in 42K+ or 86Rb+ efflux could be detected from this stimulated preparation at these concentrations. In guinea-pig portal vein, 42K+ efflux measurements were performed in the presence and absence of the dihydropyridine Ca2+ entry blocker PN 200-110 (isradipine) yielding comparable results. In the presence of PN 200-110, where spontaneous activity and the K+ efflux associated with it were abolished, the threshold concentration of cromakalim for 42K+ efflux was 0.02 mgrM as compared to 0.06 mgrM for 86Rb+ efflux. In the absence of PN 200-110, spontaneous activity of the portal vein was inhibited by 70% and 90% at these concentrations. In double isotope experiments, the K+ channel inhibitor tetraethylammonium did not discriminate between the effluxes of 42K+ and 86Rb+ stimulated by cromakalim.It is concluded that in the two vascular tissues examined, cromakalim increased the permeability to 42K+ more than to 86Rb+, the difference being more marked at low cromakalim concentrations. The use of 42K+ as the tracer ion narrows the apparent gap between the concentrations of cromakalim which elicit vasorelaxant effects and those which induce an observable increase in K+ permeability; however a significant difference persists.Part of the data was presented at the Winter Meeting of the British Pharmacological Society London 1988 Br J Pharmacol 93 (1988) p 19] Send offprint requests to U. Quasi at the above address
Keywords:BRL 34915 (cromakalim)  42K+ and 86Rb+ Efflux  K+ Channels in vascular smooth muscle  Vasorelaxation
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