Abstract
Introduction: Caveolae are small, flask-like invaginations of the plasma membrane. Caveolins are structural proteins found in caveolae that have scaffolding properties to allow organization of signaling. We have recently shown that both caveolin-1 and caveolin-3 knockout (Cav-1 KO and Cav-3 KO, respectively) mice are unable to be protected from myocardial ischemia-reperfusion injury by acute treatment with volatile anesthetics. Therefore, we tested the hypothesis that delayed cardiac protection induced by volatile anesthetics is caveolin-dependent. Methods: Biochemical assays were performed in excised hearts. Electron microscopy was used to assess caveolae formation. An in vivo mouse model of ischemia-reperfusion injury with delayed anesthetic preconditioning (delayed APC) was tested in wild-type (WT), Cav-1 KO, and Cav-3 KO mice. Mice were exposed to 30 min isoflurane or oxygen and allowed to recover for 24 h. After 24 h recovery, mice underwent 30 min left anterior descending coronary artery occlusion, followed by 2 h of reperfusion at which time infarct size was determined. Results: To elucidate a role for caveolins in delayed APC, wild-type mice were exposed to delayed APC and hearts were fractionated on a discontinuous sucrose gradient to isolate buoyant caveolar membranes. Delayed APC increased the amount of Cav-3 protein but not Cav-1 protein in buoyant fractions. Glucose transporter-4 (GLUT-4), known to interact with Cav-3 and affect cardiac protection, was also increased in buoyant fractions after APC. Microscopically distinct caveolae were observed in WT and Cav-1 KO mice but not Cav-3 KO mice. We assessed the impact of caveolae formation in induction of delayed APC. Infarct size as a percent of the area at risk was reduced by isoflurane in WT (24.0 ± 2.5% vs. 45.1 ± 2.9%, p < 0.05) and Cav-1 KO mice (27.2 ± 4.4%). Cav-3 KO mice did not show delayed APC (41.5 ± 2.2%). Conclusions: These results demonstrate that isoflurane-induced delayed preconditioning involves translocation of Cav-3 and GLUT-4 to caveolae and the presence of microscopically distinct caveolae (dependent on Cav-3 expression) are a requisite for induction of delayed protection in the myocardium. This research has received full or partial funding support from the American Heart Association, AHA Western States Affiliate (California, Nevada & Utah).
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