Extracellular calcium ion activity and reversible cardiac arrest

Abstract

The critical level of [Ca++] for reversible cardiac arrest was studied in isolated and perfused rabbit hearts. The heart could be effectively arrested by removal of Ca from the extracellular space without changing the K concentration. Chelating or Ca-binding agents such as Na or K citrate, sodium ethylenediaminetetraacetate, or oxalate were all effective in inducing arrest, but only after citrate did full recovery occur without complication. The citrate ion itself appears to have no effect directly but only through its influence on [Ca++]. At the normal range (3-5 m[image]/l) of K concentration in the perfusate, the critical [Ca++] for the onset arrest was determined to be 0. 09 m[image]/l, which is about 5% of the normal level and is uninfluenced by the citrate concentration, but is critically affected by increases in [K+] above the normal level. With an increase of [K+] from 5 to 25 mmoles/liter, the [Ca++] at which arrest is induced rises from 0. 09 to 0. 16 mM/l. The heart can be maintained in induced arrest and oxygenated by perfusion with salt solution containing 0. 09 mM/l Ca in the absence of chelating agents for long periods.