Effects of hemodynamic variables on myocardial K⁺ balance during and after shortlasting ischemia

Ischemia-induced myocardial potassium loss and post-ischemic potassium reuptake was quantitated in 8 open chest pigs during control conditions and during hemodynamic alterations which have been shown to increase steady state sarcolemmal potassium fluxes. Myocardial K⁺ balance was continuously computed before, during and after a 90 s occlusion of a branch of the circumflex artery during control (CTR), during pacing tachycardia (PACE: 34% increase in heart rate), during proximal aortic constriction (AC; 28% increase in LVSP), and during isoprenaline infusion (ISO; 135% increase in LVdP dt and 35% increase in heart rate). Ischemia-induced potassium loss increased significantly (40%) during ISO only. Higher basal metabolic rate, increased sarcolemmal K⁺ conductance, or ischemia-induced depression of a more active Na K-pump during ISO are possible explanations to why increased K⁺ loss appeared in this situation. The maximal rate of post-ischemic potassium reuptake was not different from CTR during PACE and ISO, but it was reduced during AC, which might be due to persisting subendocardial ischemia in early reperfusion when ventricular wall stress is high. The extent of potassium restoration was not different from CTR during AC, PACE and ISO.