Pharmacological and molecular comparison of K(ATP) channels in rat basilar and middle cerebral arteries

ATP-sensitive potassium (K(ATP)) channels play an important role in the regulation of cerebral vascular tone. In vitro studies using synthetic K(ATP) channel openers suggest that the pharmacological profiles differ between rat basilar arteries and rat middle cerebral arteries. To address this issue, we studied the possible involvement of endothelial K(ATP) channels by pressurized arteriography after luminal administration of synthetic K(ATP) channel openers to rat basilar and middle cerebral arteries. Furthermore, we examined the mRNA and protein expression profile of K(ATP) channels to rat basilar and middle cerebral arteries using quantitative real-time PCR (Polymerase Chain Reaction) and Western blotting, respectively. In the perfusion system, we found no significant responses after luminal application of three K(ATP) channel openers to rat basilar and middle cerebral arteries. In contrast, abluminal application caused a concentration-dependent dilatation of both arteries, that was more potent in basilar than in middle cerebral arteries. Quantitative real-time PCR detected the presence of mRNA transcripts of the K(ATP) channel subunits Kir6.1, Kir6.2, SUR1 and SUR2B, while SUR2A mRNA was barely detected in both rat basilar and middle cerebral arteries. Of the five mRNAs, the expression levels of Kir6.1 and SUR2B transcripts were predominant in both rat basilar and middle cerebral arteries. Western blotting detected the presence of Kir6.1, Kir6.2, SUR1 and SUR2B proteins in both arteries. Densitometric measurements of the Western blot signals further showed higher expression levels of Kir6.1 and SUR2B proteins in rat middle cerebral arteries than was found in rat basilar arteries. In conclusion, our in vitro pharmacological studies showed no evidence for functional endothelial K(ATP) channels in either artery. Furthermore, the results indicate that Kir6.1/SUR2B is the major K(ATP) channel complex in rat basilar and middle cerebral arteries.