Abstract
Introduction Obesity is associated with increased risk of cardiovascular and cerebrovascular disease. Alterations in artery function may underlie these effects, in particular inhibition of the large-conductance, Ca2+-activated K+-channel (BKCa) in vascular smooth muscle cells. Aims The aim of this study was to investigate the effect of diet-induced obesity on BKCa expression and function in the rat middle-cerebral artery. Methods Male Sprague-Dawley rats were maintained on a cafeteria-style, high-fat diet or standard chow (control diet) for 16-20 weeks. Responses of isolated, pressurized (80 mmHg) middle-cerebral arteries were examined. BKCa expression in the arteries was measured using real-time PCR, Western blotting and immunohistochemistry. Results Diet-induced obesity increased expression of the BKCa β1-subunit in rat middle cerebral arteries, but expression of the α-subunit was not altered. Expression of subunits was localised to vascular smooth muscle. Endothelium-dependent dilation of the arteries, induced by bradykinin, was inhibited by 50.1±5.6% (n = 5) in vessels from obese rats compared to control, but vasodilator responses to the PAR2-agonist SLIGRL (20 µM) were not affected by obesity, nor were responses to the endothelium-independent vasodilator sodium nitroprusside (SNP). In arteries from both control and obese rats, responses to bradykinin and SNP were abolished by the BKCa inhibitor iberiotoxin (0.1 µM). In arteries from control rats, SLIGRL-induced dilation was almost abolished by the combination of the NOS and guanylate cyclase inhibitors L-NAME (100 µM) and ODQ (10 µM) respectively, whereas iberiotoxin alone had no effect. In arteries from obese rats L-NAME/ODQ had only a minor effect on SLIGRL-induced dilation, but iberiotoxin inhibited SLIGRL-induced dilation by 56.3±8.1 % (n = 6). Discussion The obesity-induced increase in BKCa β1-subunit expression in rat middle cerebral arteries enabled maintenance of PAR2-induced, endothelium-dependent vasodilation, but did not prevent inhibition of BKCa-dependent responses to bradykinin.