Failure to precondition pathological human myocardium

Abstract

OBJECTIVES

We investigated the effects of ischemic preconditioning (PC) on diabetic and failing human myocardium and the role of mitochondrial K_ATPchannels on the response in these diseased tissues.

BACKGROUND

There is conflicting evidence to suggest that PC is a healthy heart phenomenon.

METHODS

Right atrial appendages were obtained from seven different groups of patients: nondiabetics, diet-controlled diabetics, noninsulin-dependent diabetics (NIDD) receiving K_ATPchannel blockers, insulin-dependent diabetics (IDD), and patients with left ventricular ejection fraction (LVEF) >50%, LVEF between 30% and 50% and LVEF <30%. After stabilization, the muscle slices were randomized into five experimental groups (n = 6/group): 1) aerobic control—incubated in oxygenated buffer for 210 min, 2) ischemia alone—90 min ischemia followed by 120 min reoxygenation, 3) preconditioning by 5 min ischemia/5 min reoxygenation before 90 min ischemia/120 min reoxygenation, 4) diazoxide (Mito K_ATPopener, 0.1 mm)—for 10 min before the 90 min ischemia/120 min reoxygenation and 5) glibenclamide (10 μm)—10 min exposure prior to PC (only in the diabetic patient groups). Creatine kinase leakage into the medium (CK, U/g wet wt) and MTT reduction (OD/mg wet wt), an index of cell viability, were assessed at the end of the experiment.

RESULTS

Ischemia caused similar injury in both normal and diseased tissue. Preconditioning prevented the effects of ischemia in all groups except NIDD, IDD and poor cardiac function (<30%). In the diazoxide-treated groups, protection was mimicked in all groups except the NIDD and IDD groups. Interestingly, glybenclamide abolished protection in nondiabetic and diet-controlled NIDD groups and did not affect NIDD groups receiving K_ATPchannel blockers or IDD groups.

CONCLUSIONS

These results show that failure to precondition the diabetic heart is due to dysfunction of the mitochondrial K_ATPchannels and that the mechanism of failure in the diabetic heart lies in elements of the signal transduction pathway different from the mitochondrial K_ATPchannels.