Abstract 3926: Effect of Replacing Cx43 With Cx32 on Myocardial Energetics and Preconditioning Protection
Connexin43 (Cx43) has been shown to be involved in preconditioning protection. We have previously demonstrated that Cx43 locates at the inner mitochondrial membrane of cardiomyocytes and influences K+ fluxes.
Objectives: to analyse the consequences of replacement of Cx43 by Cx32 on myocardial energetics and preconditioning protection in a knock-in mice in which the coding region of Cx43 is replaced by that of Cx32 (Cx43KI32).
Methods and Results: Homozygous Cx43KI32 mice did not show differences respect to wild-type animals either in QRS duration (10.25±0.27 vs 10.52±0.28 ms, p=ns) or LV fractional shortening (2D Echo) (51.35±1.41 vs 49.62±1.28%, p=ns). Isolated mitochondria obtained from hearts of Cx43KI32 homozygous mice showed reduced complex I-driven respiratory control rate (4.7 vs. 7.1, p<0.001). 31P-NMR spectroscopy of Langendorff-perfused hearts showed similar ATP and PCr levels in wild-type and homozygous mice under normoxic conditions. However, when flow was reduced to 20% of baseline, a reduction in ATP and PCr levels was observed (56.48 and 72.36% of basal values, respectively). In isolated hearts (n=81) submitted to 40min of ischemia and 60min of reperfusion, both ischemic (4 cycles of 3.5min of ischemia and 5min of reperfusion) and pharmacological (50 μmol/L diazoxide for 10 min) preconditioning protected the hearts from wild-type mice (infarct size reduction of 24.84% and 26.63%, respectively, p<0.05), but only ischemic preconditioning was effective in hearts from heterozygous animals (39.62% of infarct size reduction, p<0.05), and both ischemic and pharmacologic preconditioning failed in hearts from homozygous mice (infarct size reduction of 13.08 and −0.25%, respectively, p=ns). As positive control, protection afforded by pretreatment with 7 μmol/L cariporide was maintained in hearts from homozygous mice (reduction of 34.34%, p<0.05). In conclusion, replacement of Cx43 by Cx32 is compatible with normal cardiac function under normal conditions, but results in altered myocardial energetics and abolished preconditioning protection.