Published Online
on March 1, 2004

A more recent version of this article appeared on April 1, 2004

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Submitted on November 10, 2003
Revised on December 1, 2003

Nitric Oxide Donor Sodium Nitroprusside Dilates Rat Small Arteries by Activation of Inward Rectifier Potassium Channels

Rudolf Schubert^*; Ulrike Krien; Iris Wulfsen; Dorrit Schiemann; Gernot Lehmann; Norbert Ulfig; Ruediger W. Veh; Jürgen R. Schwarz; and Hristo Gagov

From Institute of Physiology (R.S., U.K., G.L.), University Rostock, Germany; Institute of Physiology (I.W., D.S., J.R.S.), University Hamburg, Germany; Institute of Anatomy (N.U.), RG Neuroembryology, University Rostock, Germany; Institute of Anatomy (R.W.V.), Charite, Humboldt-University, Berlin, Germany; Institute of Biophysics (H.G.), Bulgarian Academy of Sciences, Sofia, Bulgaria.

^* To whom correspondence should be addressed. E-mail: rudolf.schubert{at}medizin.uni-rostock.de.

Abstract--The role of vascular smooth muscle inward rectifier K⁺ (K_IR) channels in the mechanisms underlying vasodilation is still unclear. The hypothesis that K_IR channels are involved in sodium nitroprusside (SNP)-induced dilation of rat-tail small arteries was tested. SNP relaxed tail small arteries with an EC₅₀ of 2.6x10^-8 mol/L. Endothelium removal did not attenuate this effect. Vessel pretreatment with hydroxocobalamin, a nitric oxide (NO) scavenger, but not with rhodanese and sodium thiosulfate, inactivators of cyanide (CN), abolished the SNP effect. Vessel pretreatment with 10^-5 mol/L Ba²⁺, a specific blocker of K_IR channels at micromolar concentrations, reduced the SNP effect. Low concentrations of K⁺ dilated the vessels; this effect was attenuated largely after pretreatment with 3x10^-5 mol/L Ba²⁺. In freshly isolated smooth muscle cells, a barium-sensitive current was observed at potentials negative to the potassium equilibrium potential. Application of 10^-4 mol/L SNP increased the barium-sensitive current 1.79±0.23-fold at -100 mV and hyperpolarized the membrane potential by 8.6±0.5 mV. In tissue from freshly dissected vessels, transcripts for K_IR 2.1 and 2.2, but not for K_IR 2.3 and 2.4, were found. However, only K_IR 2.1 antibodies immunostained the tunica media of the vessel. These data suggest that vascular smooth muscle K_IR 2.1 channels are involved in the SNP-induced dilation of rat-tail small arteries.

Key words: arteries • ions • nitric oxide • potassium channels • vasodilation

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