Mechanism of Phosphate Transport Adaptation in Rat Intestinal and Renal Brush Border Membranes

Abstract

Studies on the regulation of phosphate (P_i) transport in gut and kidney have revealed an adaptation of P_i transport under dietary restriction of P_i. In response to low P_i diet, P_i absorption is enhanced in kidney and small intestine (1,2). In kidney, this stimulation results, at least in part, from the increase in the capacity of the sodium-P_i cotransport process located in the brush border membrane of the proximal tubule. The K_m of the transport process is not modified (3). It is not known, to the best of our knowledge, whether the adaptation of P_i absorption in small intestine is expressed at the brush border membrane level and how these changes occur, if any. Furthermore, since sodium is cotransported with phosphate in the luminal membrane of renal and intestinal tissues, it could be that an alteration of the dependency of the phosphate carrier on sodium played some role in the stimulation of P_i transport.