Expansion of extracellular space in the nonischemic zone of the infarcted heart and concomitant changes in tissue electrolyte contents in the rat.

The alterations in electrolyte content that occur in an infarcted zone of the heart have also been reported to occur in a similar manner, although to a far less degree, in the distant, apparently normal zones of the heart. These alterations in the nonischemic myocardium have usually been tabulated without comment, presumably because their magnitudes approach values of statistical dispersion. Our measurements of electrolyte content in the normal zone of the infarcted rat heart confirmed that all of the electrolyte contents were slightly modified. There was a rise in sodium, calcium, and chloride and a decline in potassium and magnesium. In addition, the extracellular space ([14C]sucrose) in this zone was elevated by nearly 15%. We have postulated a mechanism for this elevation based on an increase in the net filtration rate through myocardial capillaries. The expansion of the extracellular space can account for all of the electrolyte changes in the normal zone with the exception of the alteration in calcium. Therefore, there is no basis for assuming that these myocardial alterations reflect general movements of electrolytes down their electrochemical gradients. We suggest that the increment in the nominal concentration of cellular calcium is related to a compensatory mechanism that allows the reduced mass of functional myocardium to contract more vigorously.