PHOSPHATE DEPRIVATION INHIBITS NH(4+) TRANSPORT IN OK CELLS

Deprivation of dietary phosphate leads to a decrease in urinary excret ion of ammonium in rats which may be mediated through an alteration in ammonium transport in the proximal tubule. In the present study the O K renal epithelial cell line, a model for the proximal tubule, was use d to determine if NH4+ transport was changed during acute phosphate de privation. The intracellular pH after perfusion with NH4Cl solution wa s used for calculation of intracellular NH4+ concentration. Intracellu lar [NH4+] increased linearly during the first 2 min of acidification with NH4Cl. NH4+ transport, defined by the initial rate of the increas e in intracellular [NH4+], was decreased by 32% (P < 0.005) in phospha te-deprived cells. This transport process was inhibited by barium chlo ride, but not by DIDS, amiloride or ouabain, suggesting that the NH4transport pathway may utilize K+ channels. Acute phosphate deprivation may inhibit NH4+ transport in OK cells by decreasing membrane K+ perm eability.