Abstract 15914: Mitochondrial Short Form Sulfonylurea Receptors-2A Splice Variant Protects Hearts From Ischemia Reperfusion Injury.
Sulfonylurea receptor-2 is a subunit of ATP-sensitive K-channels (KATP) that have been implicated in protecting hearts from ischemia reperfusion (I/R) injury. Surprisingly, SUR2 knockout (SUR2KO) male mice are protected against I/R injury. A 55kDa intra-exonic splice variant of SUR2A (SUR2A-55) unique to mitochondrial membrane fractions forms functional KATP channels and is more abundant in mitochondria of SUR2KO mice than in wild type (Wt). We hypothesized that increased expression of SUR2A-55 protects hearts from I/R injury. We established three transgenic (Tg+) mouse lines with 1, 3 or >5 copies of the SUR2A-55 transgene using a cardiac specific α-MHC promoter in the Wt background. Cardiac specific mitochondrial expression of SUR2A-55 increased in the order Wt < Tg+1 < Tg+3 < Tg+5 by immunoblotting and RT-PCR. Survival of the Tg+5 mice was low presumably due to toxic over-expression. After 30 min ischemia and 24 h reperfusion, the infarct sizes in Tg+1 (10±3%, n=11, p<0.05) and Tg+3 (7±3%, n=9, p<0.001) were smaller compared with Wt littermates (18±4%, n=12) by triphenyltetrazolium chloride staining. Echocardiography showed no difference in cardiac functions of Tg+1, Tg+3 or Wt before infarction. After infarction, end-diastolic left ventricular volume (LVEDV) increased by 1.3±1 μL in Tg+3 compared with 5.2±2 μL in Wt mice (n=4, p<0.05) and, ejection fraction (EF) decreased by 5.8±2 % in Tg+3 compared with 11.1±2% in Wt mice (n=4, p<0.05). Isolated myocytes were exposed to no-glucose-no-oxygen buffer (ischemia) followed by normal tyrode (reperfusion) for 30 min each. More myocytes (n=16–20) from Tg+1 (29±9%, p<0.05) or Tg+3 (53±8%, p<0.0001) mice survived the protocol compared with Wt (16±6%). KATP channels have been implicated in maintenance of the mitochondria membrane potential (Δψ) and; thus, Δψ was estimated by rhodamine fluorescence in myocytes (n=8–10). The Δψ depolarized more slowly in Tg+ lines and, at the end of the reperfusion, was less depolarized in Tg+1 (27±8%, p<0.05) or Tg+3 (11±4%, p<0.001) myocytes compared with Wt (49±11%). In conclusion, over-expression of SUR2A-55 reduces infarct size and maintains cardiac function with improved maintenance of Δψ. Detrimental over-expression in Tg+5 remain to be studied.
- © 2010 by American Heart Association, Inc.