Abstract 1293: SUR2 Disrupted Mice Protected from Ischemia by Mechanism Distinct from Classical Preconditioning
The cell surface cardiac ATP-sensitive potassium channel (cellKATP) is formed by a KIR6.x pore and a SUR2 regulatory subunit. In an earlier attempt to “knock out” KATP channels, a disruption cassette was introduced in wild-type (WT) mouse to disrupt the sequence between exons 10 and 21 of the SUR2 gene. The full-length 150-kDa SUR2 and cellKATP activity were both absent from the sur2 mutant heart, as was the diazoxide-induced mitochondrial autofluorescence. Infarctions were created by 30-min coronary ligature and sized after 90 min reperfusion in both the WT and the sur2 mutant, with and without acute and delayed (24 hr) ischemic preconditioning protocols (APC and DPC). Infarct sizes were computed as infarct area relative to area at risk for WT: sham, 37.96±1.78% (n=10); APC, 25.28±1.87 % (n=11) and DPC, 27.40±4.45% (n=5), whereas for the sur2 mutant: sham, 24.04±3.73% (n=10); APC, 18.87±1.13% (n=10) and DPC, 21.14±2.81% (n=5). Thus, the sur2 mutant mice had significantly smaller infarctions than WT as if they were pre-protected, and both forms of preconditioning produced only marginal improvements in infract sizes. These mice had previously been shown to have spontaneous coronary vasospasm, but known protein markers of preconditioning (Hsp70, Bcl2) were found to be not elevated suggesting the classical preconditioning might not be the mechanism for this protection. We then used RACE/nested PCR and a panel of antibodies to identify 55-kDa SUR2A and SUR2B in purified heart mitochondria of WT, and surprisingly of the mutant sur2 mice as well. The identifications of the sequences encoding the SUR2 short forms suggests that they are generated by post-transcriptional modifications, which are not affected by the insertion of the disruption cassette. Thus, this sur2 mutant mouse may contain the critical components for the cardiac mitoKATP channels, which confer cardioprotection during ischemia, but the mechanism, at present unknown, may be distinct from classical acute and delayed preconditioning.