Dissociation of cell volume regulation and sodium-potassium exchange pump activity in dog myocardium in vitro

The relation between myocardial cell potassium and water contents after hypoxia at 0°C (cold shock) in Krebs-Ringers-Phosphate solution was studied using 252 myocardial slices from six dogs. Losses of potassium were marked and similar after immediate cold shock, cold shock after 1 h equilibration in oxygenated media at 25°C and immediate cold shock plus 1 m m ouabain. However, myocardial water and total monovalent cations were only slightly increased by cold shock after equilibration compared to the marked increases found after immediate cold shock with and without ouabain ( P < 0.01). When edematous slices were warmed to 25°C in oxygenated media, myocardial potassium increased towards control values in the absence of ouabain ( P < 0.01) and decreased further when ouabain was present ( P < 0.01), but in both cases myocardial water and total monovalent cations decreased towards control values ( P < 0.01). This dissociation of NaK exchange pump activity and myocardial cell volume regulation can be only partially explained using the classic “pump-leak” theory of cell volume regulation.