Objective  To investigate the effect of preconditioning with mitochondrial ATP-sensitive potassium channel opener on the mitochondrial functions.   Methods  Thirty SD rats were used. Isoproterenol was used to induce myocardial ischemic injury in 20 rats

ten of which were pretreated with diazoxide. Rhodamine123 (Rh123) was used as fluorescent prober to measure mitochondrial membrane potential. The activities of mitochondrial Na

+

K

+

-ATPase and Ca

2+

-ATPase were detected. The mitochondrial respiratory parameters were recorded with a Clark electrode. The effect of diazoxide on mitochondrial membrane potential and mitochondrial respiration was investigated.   Results  Compared with the controls

the levels of state 3 (ST3)

respiratory control rate (RCR)

mitochondrial membrane potential content and the activities of mitochondrial ATPase were decreased in the rats that received isoproterenol

while diazoxide pretreatment alleviated the changes of ST3

RCR

mitochondrial membrane potential and the activities of mitochondrial ATPase.   Conclusion  Preconditioning with diazoxide enhances the activities of mitochondrial ATPase and protects the myocardial mitochondrial function after isoproterenol induced myocardial ischemic injury.