Cardiac Sarcolemmal Na+/H+ Exchange after a Myocardial Infarction in the Rat
A growing number of studies have implicated the Na+/H+ exchanger in ischemic/reperfusion damage to the heart [1–7]. Other studies have now demonstrated accelerated ion flow through this exchanger in hypoxic/ reoxygenation insult to the heart as well [8–10]. While these are important pathological events, they are largely immediate reactions of Na+/H+ exchange activity in response to changes in the intracellular ionic environment in the heart. These reactions occur so quickly that they likely do not involve structural changes in the protein or alterations in protein synthesis. However, during low-flow ischemia of a relatively long duration, there are indications that these pathways are beginning to be activated. Changes in the Na+/H+ exchange mRNA message have been detected in hearts after three hours of low-flow ischemia . These changes do not occur in global ischemia experiments, which employ considerably shorter ischemic periods (≤1 hour) [11,12]. Chronic alterations in the exchanger would be more likely to occur during conditions where an adaptive stimulus is placed upon the heart for a much longer period of time and/or where the tissue is allowed sufficient time to induce its adaptive mechanisms. A stimulus that frequently induces an adaptive response in the heart is myocardial disease.
KeywordsCholesterol Sucrose Depression Ischemia Washout
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