Different effects of phenylephrine and clonidine on 86Rb efflux and on contraction in the rat caudal artery

KCa channel blockers reveal hyperpolarization and relaxation to K+ in rat isolated mesenteric artery

“…Because stimulation of smooth muscle cells with constrictor agonists is associated with the activation of K Ca channels, increasing stimulation will be associated with an increase in the efflux of K ϩ through these channels. Evidence that phenylephrine can stimulate K ϩ efflux came originally from monitoring 86 Rb efflux (6). In the present study, the degree of activation of the K Ca is indicated by the effect on the contraction to phenylephrine.…”

“…An additional source for [K ϩ ] o is the artery wall itself, where stimulation of both smooth muscle and endothelial cells is associated with K ϩ efflux (2,6,12,16). Ca 2ϩ -activated K ϩ channels (K Ca ) provide the predominant route for this K ϩ efflux, and the activity of these channels has important functional consequences in the regulation of myogenic tone (3,24).…”

“…One possibility is that antagonism results from an increasing efflux of K ϩ from both the smooth muscle and endothelial cells, as the intensity of stimulation with phenylephrine increases. Stimulation of both cell types is known to be associated with a significant efflux of K ϩ (2,6,12,16). K Ca provide a predominant route for the efflux, and not surprisingly these channels have very important functional consequences.…”