title: Phosphate transport in Ehrlich ascites tumor cells: inhibition by H+.
abstract: The effect of changes in extracellular pH (pHo) and intracellular pH (pHi) on Na+-dependent and Na+-independent inorganic phosphate (Pi) transport in Ehrlich cells was investigated. In the presence of Na+, acutely reducing pHo from 7.30 to 5.50 results first in a transient (approximately 7 min) stimulation of Pi transport. The enhanced rate of transport is a saturable function of the extracellular [H+]; the Ks equals 2.3 X 10(-6) M (pHo 6.68). However, Pi transport is progressively inhibited as pHi falls below 6.50. The effect of pHi on Pi transport measured at various intracellular [Na+] suggests that inhibition develops as a consequence of H+ interaction with an intracellular Na+ site(s) on the Na+-dependent carrier. At pHo 7.4, about 15% of the steady state Pi flux persists in the absence of Na+. However, when pHo is reduced, transport is stimulated to the same extent and with the same time course and kinetic characteristics as in the presence of Na+. Thus, H+ stimulated Pi transport does not require Na+, raising the possibility that the Na+-independent component is mediated by the anion (Cl-) exchanger.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001693:Biological Transport, Active; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010710:Phosphates / Q000378:metabolism*; D011522:Protons; D012964:Sodium / Q000378:metabolism
chemical_list: D007473:Ion Channels; D010710:Phosphates; D011522:Protons; D012964:Sodium