Spontaneous coronary vasospasm in KATP mutant mice arises from a smooth muscle-extrinsic process

In the vasculature, ATP-sensitive potassium channels (K-ATP) channels regulate vascular tone. Mice with targeted gene disruptions of K-ATP subunits expressed in vascular smooth muscle develop spontaneous coronary vascular spasm and sudden death. From these models, it was hypothesized that the loss of K-ATP channel activity in arterial vascular smooth muscle was responsible for coronary artery spasm. We now tested this hypothesis using a transgenic strategy where the full-length sulfonylurea receptor containing exon 40 was expressed under the control of a smooth muscle-specific SM22 alpha promoter. Two transgenic founder lines were generated and independently bred to sulfonylurea receptor 2 (SUR2) null mice to generate mice that restored expression of K-ATP channels in vascular smooth muscle. Transgenic expression of the sulfonylurea receptor in vascular smooth muscle cells was confirmed by detecting mRNA and protein from the transgene. Functional restoration was determined by recording pinacidil-based K-ATP current by whole cell voltage clamping of isolated aortic vascular smooth muscle cells isolated from the transgenic restored mice. Despite successful restoration of K-ATP channels in vascular smooth muscle, transgene-restored SUR2 null mice continued to display frequent episodes of spontaneous ST segment elevation, identical to the phenotype seen in SUR2 null mice. As in SUR2 null mice, ST segment elevation was frequently followed by atrioventricular heart block. ST segment elevation and coronary perfusion pressure in the restored mice did not differ significantly between transgene-negative and transgene-positive SUR2 null mice. We conclude that spontaneous coronary vasospasm and sudden death in SUR2 null mice arises from a coronary artery vascular smooth muscle-extrinsic process.