[The relationship between Na overload and Na/H exchange--a study in the isolated isovolumic rat hearts]

Thirty min after stabilization perfusion with oxygenated buffer, hearts were divided in four groups: (1) CONTROL GROUP: 75 min. of aerobic perfusion; (2) Low flow anoxia group: 45 min. of low flow anoxic perfusion (95% N2:5%CO2, 0.15 ml/min.) followed by 30 min. of aerobic perfusion; (3) Ouabain group: protocol same as (2), except that ouabain (200 mumol/L) was added to anoxic perfusate during low flow anoxia; (4) Ouabain+Amiloride group: protocol same as (3) except that amiloride (0.5 mmol/I) was added to perfusate during low flow anoxia. Compared with the low flow anoxia group, ouabain resulted in an additional increase in Na during reperfusion accompanied with a depressed ventricular function. The deleterious effects of ouabain could be significantly combatted by amiloride. It is concluded that a decrease in Na/K ATPase activity may contribute to Na gain in reperfused myocardium, the mechanism of which might result from stimulation of Na/H exchange.