Pfluegers Archiv/European Journal of Physiology 2006-10-01

Dual effect of initial [K] on vascular tone in rat mesenteric arteries.

Didier X P Brochet, Philip D Langton

文献索引：Pflugers Arch. 453(1) , 33-41, (2006)

全文：HTML全文

摘要

A slight increase in extracellular concentration of potassium ([K(+)](o)) can act as a vasodilator in rat mesenteric vascular bed. However, in recent years, several groups have failed to consistently observe relaxation of rat mesenteric arteries in these conditions. The aim of the present study was to provide a mechanistic understanding of this discrepancy. In rat small mesenteric arteries, 37 of 40 arteries mounted for measurement of isometric force and pre-contracted with phenylephrine (PE) did not relax when ([K(+)](o) was raised from 5.9 mM (control ([K(+)](o) to 11.2 or 21.2 mM. However, when ([K(+)](o) was briefly lowered to 1.2 mM, increasing ([K(+)](o) to between 5.9 and 41.2 mM evoked relaxation. This relaxation was not reduced by barium or by removal of the endothelium, but was abolished by 0.1 mM ouabain. Raising ([K(+)](o) from concentrations between 0 and 5.9 mM to 13.8 mM elicited a relaxation of PE-induced tone that was inversely proportional to initial ([K(+)](o). Relaxation was associated with a ouabain-sensitive hyperpolarization of smooth muscle cells. In arteries exposed to dihydroouabain (DHO), raising ([K(+)](o) from 5.9 to 13.8 mM and simultaneously washing out DHO resulted in relaxation of PE-induced force. These results suggest that only when the initial ([K(+)](o) is less than approximately 5 mM do small elevations in ([K(+)](o) evoke smooth muscle hyperpolarization and relaxation via activation of Na,K-ATPase, and not inwardly rectifying K(+) channels. Therefore, small differences in the initial ([K(+)](o) (4.6 vs 5.9 mM) can strongly influence the variations of vascular tone to increases in ([K(+)](o).