Role of vascular K(ATP) channels in blood pressure variability after sinoaortic denervation in rats

Abstract

Aim: To investigate the role of ATP-sensitive potassium (K(ATP)) channels on blood pressure variability (BPV) in sinoaortic denervated (SAD) rats.

Methods: SAD was performed on male Sprague-Dawley rats 4 weeks before the study. mRNA expression of Kir6.1, Kir6.2 and SUR2 in aorta and mesenteric artery was determined using real-time quantitative polymerase chain reaction, and confirmed at the protein level using Western blotting and laser confocal immunofluorescence assays. Concentration-response curves of isolated aortic and mesenteric arterial rings to adenosine and pinacidil were established. Effects of K(ATP) channel openers and blocker on BPV were examined in conscious SAD rats.

Results: Aortic SUR2 expression was significantly greater, while Kir6.1 was lower, in SAD rats than in sham-operated controls. In contrast, in the mesenteric artery both SUR2 and Kir6.1 expression were markedly lower in SAD rats than controls. For both arteries, Kir6.2 expression was indistinguishable between sham-operated and SAD rats. These findings were confirmed at the protein level. Responses of the aorta to both adenosine and pinacidil were enhanced after SAD, while the mesenteric response to adenosine was attenuated. Pinacidil, diazoxide, nicorandil, and glibenclamide significantly decreased BPV.

Conclusion: These findings indicate that expression of vascular K(ATP) channels is altered by chronic SAD. These alterations influence vascular reactivity, and may play a role in the increased BPV in chronic SAD rats.

Figure 1

Expression of Kir6.1, Kir6.2 and SUR2 in both aorta and mesenteric artery in sinoaortic denervated and sham-operated rats. A and B, fold changes of mRNA level (Kir6.1, Kir6.2, and SUR2) in aorta and mesenteric artery (n=7). C and D, fold changes of protein level (Kir6.1, Kir6.2, and SUR2) in aorta and mesenteric artery (n=3). The representative images are from three independent experiments. Data are expressed as mean±SEM. ^bP<0.05, ^cP<0.01 vs sham-operated rats by unpaired Student's t-test.

Figure 2

Representative images of Kir6.1, Kir6.2, and SUR2 expression in aorta (A–C) and mesenteric artery (D–F) from sinoaortic denervated (SAD) and sham-operated rats using laser scanning confocal microscopy. Aortic SUR2 expression was greater, while Kir6.1 was lower, in SAD rats than in sham-operated controls (A and C). In the mesenteric artery both SUR2 and Kir6.1 expression were markedly lower in SAD rats than controls (D and F). For both arteries, Kir6.2 expression was indistinguishable in sham-operated compared with SAD rats (B and E). Similar images were observed in vessels from at least 3 rats for each group. FITC,fluorescein isothiocyanate; DIC, differential interference contrast. The objective was ×20, scale bar: 50 μm.

Figure 3

Vasodilatation induced by adenosine and pinacidil in phenyl-ephrine-precontracted intact rat aorta (A, B) and mesenteric artery (C, D). Relaxant responses are expressed as the percentage reduction in tension produced by phenylephrine. Each point represents mean±SEM. (thoracic aorta, 17–21 aortic rings obtained from 9–12 rats; superior mesenteric artery, 12 superior mesenteric arterial rings from 9–12 rats). Sham, sham operation. ^cP<0.01 vs sham-operated rats by repeated measures analysis of variance.

Figure 4

Effects of K_ATP channel openers and blocker on blood pressure variability (BPV) in sinoaortic denervated (SAD) rats. Pinacidil (n=10), diazoxide (n=8), nicorandil (n=8), and glibenclamide (n=10) significantly decreased BPV. SBPV, systolic BPV; DBPV, diastolic BPV. Data are expressed as mean±SEM. ^cP<0.01 vs isotonic saline by paired t-test.