Rosiglitazone induces arrhythmogenesis in diabetic hypertensive rats with calcium handling alteration.
ABSTRACT BACKGROUND: Diabetes and hypertension have significant effects on cardiac calcium (Ca(2+)) regulation, which plays an essential role in determining cardiac function. The effect of peroxisome proliferator-activated receptor (PPAR)-γ agonists on Ca(2+) regulation in the cardiomyocytes is unclear. OBJECTIVE: The purpose of this study was to investigate the effects of hypertension, diabetes, and PPAR-γ agonist-rosiglitazone on the regulation of Ca(2+) and the electrophysiological characteristics of isolated ventricular myocytes. METHODS: The indo-1 fluorometric ratio technique and whole-cell patch clamp were used to investigate intracellular Ca(2+) (Ca(2+)(i)), action potentials, and ionic currents in ventricular myocytes from rats of Wistar-Kyoto (WKY), diabetic WKY (induced by streptozotocin), diabetic WKY treated with rosiglitazone (5mg/kg), spontaneously hypertensive rats (SHR), diabetic SHR, and diabetic SHR treated with rosiglitazone. Western blot was used to evaluate protein expressions of sarcoplasmic reticulum ATPase (SERCA2a), Na(+)-Ca(2+) exchanger (NCX), and ryanodine receptor (RyR). RESULTS: Diabetic WKY and diabetic SHR had smaller sarcoplasmic reticulum Ca(2+) contents, and Ca(2+)(i) transients with a prolonged decay portion, down-regulated SERCA2a, NCX, and RyR protein expressions and smaller L-type Ca(2+) currents than non-diabetic WKY and SHR, respectively. The Ca(2+) dysregulations in diabetes were attenuated in rats treated with rosiglitazone. Diabetes and hypertension both prolonged the action potential duration which were enhanced by the use of rosiglitazone, and induced the genesis of triggered activity. CONCLUSIONS: Diabetes and hypertension modulate Ca(2+) handling. Rosiglitazone significantly changed the Ca(2+) regulation and electrophysiological characteristics, and may contain an arrhythmogenic potential in diabetes with hypertension.