Renal potassium transport: morphological and functional adaptations.
Maintenance of K+ homeostasis in mammals and amphibians depends primarily on the kidneys which excrete 95% of K+ ingested in the diet. The amount of K+ in the urine is determined by the rate of K+ secretion or absorption by the distal tubule and the collecting duct. When K+ intake is increased, K+ secretion rises. The mechanisms of K+ secretion by the distal tubule and collecting duct are so efficient that K+ intake can increase 20-fold with little or no increase in body K+ content or in plasma K+ concentration. Elevated K+ secretion by the distal tubule and collecting duct occurs in part because of an increase in the quantity of Na+-K+-adenosinetriphosphatase (Na+-K+-ATPase) and amplification of the basolateral membrane of principal cells. When dietary K+ intake is reduced, urinary K+ excretion falls, because K+ secretory mechanisms are suppressed and K+ absorptive mechanisms, residing in the distal tubule and collecting duct, are activated. Because a low-K+ diet is associated with hypertrophy of intercalated cells, it has been suggested that this cell type absorbs K+, possibly by an H+-K+-ATPase. In this review, I discuss the functional and morphological evidence that supports the view that principal cells secrete K+ and that intercalated cells absorb K+. In addition, some of the hormones and factors that are responsible for these changes in cell structure and function are discussed.
Stanton
B A
BA
Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03756.
D000222:Adaptation, Physiological; D000818:Animals; D001692:Biological Transport; D001696:Biomechanical Phenomena; D004032:Diet; D007668:Kidney / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D007685:Kidney Tubules, Collecting / Q000648:ultrastructure; D007686:Kidney Tubules, Distal / Q000648:ultrastructure; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology / Q000652:urine
D011188:Potassium