Abstract: Objective To study the contribution of mitochohondrial adenosine triphosphate (ATP)-sensitive potassium channel (mitoK_ATP) in the antihypertrophic effect of quercetin(Que) in neonatal rat ventricular myocytes.Methods Myocardial cells of neonatal rats were cultured in vitro.The hypertrophic myocytes were induced by phenylephrine(PE) 10 μmol·L^-1 and then different doses of Que(25,50,100 μmol·L^-1) were administered.Antihypertrophic effects of Que stimulation under administration of 100 μmol/L of 5-hydroxydecanoic acid (5-HD),a specific blocker of mitochondial K_ATP channel,was also observed.The total protein content was measured with Lowry method.The cardiomyocyte size was measured by computer photograph analysis system.The expression of atrial natriuretic peptide(ANP) mRNA was determined with reverse transcription polymerase chain reaction (RT-PCR).The expression of K_ir6.2 was determined by Western blot.Results PE increased the total protein content (27.45±2.45 μg),the cardiomyocytes size (2 278±156 μm³),and the expression of ANP mRNA.Que (50,100 μmol/L)showed a dose-dependent function,with the reduction of total protein content (21.15±1.39 to 19.28±2.23 μg),cardiomyocytes size (1 656±230 to 1 398±298 μm³),the expression of ANP mRNA,and the expression of K_ir6.2 in the absence of 5-HD.Conclusion The results suggest that the inhibitory effect of Que on PE-induced hypertrophy may involve mito K_ATP.