Nitration and Functional Loss of Voltage-Gated K⁺ Channels in Rat Coronary Microvessels Exposed to High Glucose

Abstract

Coronary microvessels generate reactive oxygen species in response to high glucose (HG), resulting in vasodilator defects involving an impaired function of vascular K⁺ channels. Inhibition of voltage-gated K⁺ (K_v) channels by peroxynitrite (ONOO⁻), formed by the interaction of superoxide and nitric oxide, may contribute to impaired dilation. The present study investigated whether HG induces ONOO⁻ formation to mediate nitration and impairment of K_v channels in rat small coronary arteries (RSCAs). Exposure to ONOO⁻ reduced the dilator influence of K_v channels in RSCAs. Patch-clamp studies revealed that ONOO⁻ diminished whole-cell and unitary K_v currents attributable to the K_v1 gene family in smooth muscle cells. Subsequently, immunohistochemically detected enhancement of nitrotyrosine residues in RSCAs that were cultured in HG (23 mmol/l) compared with normal glucose (5.5 mmol/l) for 24 h correlated with the nitration of K_v1.2 channel α-subunits. HG-induced nitrotyrosine formation was partially reversed by scavenging ONOO⁻. Finally, RSCAs that were exposed to HG for 24 h showed a loss of K_v channel dilator influence that also was partially restored by the ONOO⁻ scavengers urate and ebselen. We conclude that ONOO⁻ generated by HG impairs K_v channel function in coronary microvessels, possibly by nitrating tyrosine residues in the pore-forming region of the K_v channel protein.