Sodium and potassium ion transport accelerations in erythrocytes of DOC, DOC-salt, two-kidney, one clip, and spontaneously hypertensive rats. Role of hypokalemia and cell volume.

Abstract

Sodium (Na+) and potassium (K+) transport by the furosemide-sensitive Na+-K+ transport system, the Na+-K+ pump, and the cation leak(s) were studied in erythrocytes from DOC-water, DOC-salt, two-kidney, one clip (Sprague-Dawley), and spontaneously hypertensive rats (Wistar-Kyoto). Rubidium (Rb+) was used as a tracer for K+. After 4 weeks of DOC-salt hypertension, inward K+ (Rb+) transport by the furosemide-sensitive system was increased threefold, and the inward Na+ leak and the red cell Na+ content were elevated by about 50%. The rise in cell Na+ accelerated K+ inward and Na+ outward transport by the Na+-K4 pump, DOC-water hypertension caused similar but less pronounced changes. In two-kidney, one clip hypertension, the Na+ leak and the Na+-K+ pump rates were slightly elevated, and furosemide-sensitive Rb+ uptake tended to be increased. In spontaneously hypertensive rats, furosemide-sensitive Rb+ uptake was accelerated by 50%. The marked hypokalemia in DOC-water and DOC-salt hypertension was associated with a slight loss of red cell K+ and an increase in mean cellular hemoglobin content (MCHC), indicative of cell shrinkage. Hypokalemia induced by dietary K+ deficiency caused alterations in red cell cation transport, content, and cell volume which were qualitatively similar but more pronounced than those seen in DOC-salt hypertension. Osmotic shrinkage in vitro induced a severalfold acceleration of furosemide-sensitive Rb+ uptake, similar to that observed in rat erythrocytes shrunken in vivo in K+-deficient states. It is concluded that the acceleration of furosemide-sensitive K+ (Rb+) transport in erythrocytes of mineralocorticoid hypertensive rats is largely caused by the hypokalemia and consecutive red cell K+ loss and shrinkage, respectively. Mean cellular hemoglobin content (MCHC) is thus a parameter that must be considered in studies on Na+ and K+ transport across the membrane of rat erythrocytes.