Potassium efflux from the myocardium during hypoxia: role of lactate ions.

To determine the role of lactate in the causation of potassium efflux during hypoxia, the effect of lactate ions on the uptake and efflux of 42potassium was studied in the isolated arterially perfused interventricular septum of the rabbit. Septa were equilibrated with lactate (50 mmol.litre-1) under isosmotic conditions before switching to a perfusate containing the inert and impermeant anion isethionate (50 mmol.litre-1). A reduction in tissue 42potassium content was detected, which could only partly be accounted for by increased efflux. During hypoxic substrate free perfusion potassium loss was due to an increased efflux with no evidence of altered influx. The extrusion of accumulating anions, such as lactate ions, from the myocardium is one mechanism for the early potassium loss during hypoxia.