The Influence of Changes in pH of the Perfusion Fluid on the Occurrence of the Calcium Paradox in the Isolated Rat Heart

AUTHOR’S YNOPSIS. During Lungendor-perfusion of isolated rat hearts the minimum duration of the calcium-jiree perfusion period, after which reperfusion with calcium evokes the “ calcium paradox”, is influenced by changes in pH of the perfision fluid. and shortened by an increased pH. Calcium ions play a dominant role in muscle con-traction. Flux of this cation across the cell mem-brane is determined by many factors, one of which is probably the concentration of extracellular and intracellular hydrogen ions (Judah, Ahmed, Mc-Lean, and Christie, 1965; Wallach, Reizenstein, and Bellavia, 1966). It has been shown (Wallach et al., 1966) that the coefficients of influx and efflux of the calcium ions in the liver cell increase with an alkalotic pH and decrease with an acidotic pH of the extracellular medium. Judah et al. (1965) found that the transport of calcium, mag-nesium, and potassium ions into the mitochondria from the rat liver cell depends on the efflux of hydrogen ions from mitochondria. Zimmerman and Hulsmann (1966) introduced the term “calcium paradox ” for the following observation: after perfusion of isolated rat hearts with calcium-free perfusion fluid for. more than 3 min, followed by reintroduction of the normal calcium-containing perfusion fluid, a loss of electri-cal and mechanical activity of the heart occurs, as well as extensive morphological changes and loss of the heart cell contents (Zimmerman, Daems, Huls-mann, Snijder, Wisse, and Durrer, 1967). They postulated that this “calcium paradox ” is caused by an excessive influx of calcium ions into the myocardial cells, resulting in the destruction of larg