Potassium Channel Dysfunction in Cerebral Arteries of Insulin-Resistant Rats Is Mediated by Reactive Oxygen Species

Abstract

Background and Purpose-Insulin resistance (IR) increases the risk of stroke in humans. One possible underlying factor is cerebrovascular dysfunction resulting from altered K+ channel function. Thus, the goal of this study was to examine K+ channel-mediated relaxation in IR cerebral arteries. Methods-Experiments were performed on pressurized isolated middle cerebral arteries (MCAs) from fructose-fed IR and control rats. Results-Dilator responses to iloprost, which are BKCa channel mediated, were reduced in the IR compared with control arteries (19±2% versus 33±2% at 10-6 mol/L). Similarly, relaxation to the KATP opener pinacidil was diminished in the IR MCAs (17±2%) compared with controls (38±2% at 10-5 mol/L). IR also reduced the KATP channel-dependent component in calcitonin gene-related peptide-induced dilation; however, the magnitude of the relaxation remained unchanged in IR because of a nonspecified K+ channel-mediated compensatory mechanism. In contrast, Kir, channel-mediated relaxation elicited by increases in extracellular [K+] (4 to 12 mmol/L) was similar in the control and IR arteries. Blockade of the Kir and Kv channels with Ba2+ and 4-aminopyridine, respectively, constricted the MCAs in both experimental groups with no significant difference. Pretreatment of arteries with superoxide dismutase (200 U/mL) plus catalase (150 U/mL) restored the dilatory responses to iloprost and pinacidil in the IR arteries. Immunoblots showed that the expressions of the pore-forming subunits of the examined K + channels are not altered by IR. Conclusions-IR induces a type-specific K+ channel dysfunction mediated by reactive oxygen species. The alteration of KATP and BKCa channel-dependent vascular responses may be responsible for the increased risk of cerebrovascular events in IR.