Abstract 183: Improved Ca-cycling by Dexamethasone Preserves Contractility After Ischemia/Reperfusion in Diabetic Rat Cardiomyocytes

Abstract

Glucocorticoid receptor (GR) stimulation is essential for normal heart function and dexamethasone (DEX) treatment has been shown to reduce ischemia reperfusion injury (IRI). Prevalence of diabetes is increasing and myocardial infarction in such patients is more severe and risk of complications is augmented. We tested the hypothesis, that GR stimulation with DEX protects diabetic myocardium from IRI by improving Ca cycling. Cardiomyocytes from type 2 diabetic Zucker diabetic fatty rats were isolated and cultured in DEX (10 μg/mL) vs. vehicle for 24h. [Ca] i and fractional shortening (FS) was measured in electrical field-stimulated cardiomyocytes loaded with Fura-2 AM (10 μM). Compared to control, DEX-treated cells display increased Ca transient amplitude (0.33±0.03 vs. 0.46±0.04, P = 0.01, n=6 animals) and FS (fig.) DEX also significantly increased sarcoplasmic reticulum (SR) Ca content (Caffeine, 10 mM) and reduced SR Ca leak measured as Ca spark frequency (SpF), fluo-4 loaded myocytes, confocal microscopy (fig.). To test, whether DEX reduced IRI, rats were treated with DEX (2 mg/kg i.p.) 24h before measurement (vehicle as control). Left ventricular developed pressure (LVDP) was monitored in Langendorff-perfused-hearts during global ischemia for 30 min and reperfusion. During reperfusion, DEX-treated hearts showed significantly greater LVDP (P < 0.05, 2way ANOVA, fig.). In diabetic rats, glucocorticoid receptor stimulation with DEX leads to a more efficient Ca cycling with reduced SR Ca leakage, which translates to an increased contractility on the cellular level and protection against ischemia reperfusion injury in the whole organ.