Na+ accumulation increases Ca2+ overload and impairs function in anoxic rat heart.

Area of Science:

• Cardiology
• Physiology
• Biochemistry

Background:

• Global ischemia and subsequent reoxygenation lead to significant cardiac dysfunction.
• Calcium (Ca2+) overload and intracellular sodium (Na+) accumulation are key factors in reperfusion injury.
• The role of Na+, K+-ATPase activity in preserving cardiac function during ischemia-reperfusion is not fully understood.

Purpose of the Study:

• To investigate the protective effects of low coronary flow during anoxia on isolated rat hearts.
• To determine the mechanisms underlying the observed functional recovery and prevention of Ca2+ overload.
• To elucidate the contribution of intracellular Na+ accumulation and ATP depletion to reperfusion injury.

Main Methods:

• Isolated rat hearts were subjected to anoxia with either normal or low coronary flow (1 ml/min).
• Hearts were reperfused, and functional recovery, end-diastolic pressure (LVEDP), and Ca2+ uptake were measured.
• Intracellular Na+ (Nai+) and ATP levels were assessed under various conditions, including substrate availability, ouabain treatment, and monensin exposure.

Main Results:

• Low coronary flow during anoxia maintained cardiac function and prevented Ca2+ overload during reperfusion.
• Global ischemia led to impaired recovery, increased LVEDP, and elevated reperfusion Ca2+ uptake, associated with increased Nai+.
• Substrate provision preserved ATP and lowered Nai+ during anoxia; ouabain and monensin impaired recovery by increasing Nai+ without significantly altering ATP.

Conclusions:

• Maintenance of Na+, K+-ATPase activity is crucial for preventing intracellular Na+ accumulation during anoxia.
• Reduced Nai+ accumulation, facilitated by low coronary flow, is the primary mechanism protecting against reperfusion injury.
• Targeting Na+ handling offers a promising therapeutic strategy for mitigating cardiac ischemia-reperfusion damage.