Na-P(i) cotransporter type I activity causes a transient intracellular alkalinization during ATP depletion in rabbit medullary thick ascending limb cells.
The cellular pathophysiology of renal ischemia-reperfusion injury was investigated in primary cell cultures from rabbit medullary thick ascending limb (MTAL). Metabolic inhibition (MI) was achieved with cyanide and 2-deoxyglucose. Sixty minutes of MI caused a profound but reversible decrease in intracellular concentration of ATP ([ATP]i). Intracellular pH (pHi) first decreased after initiation of MI, followed by a transient alkalinization. When [ATP]i reached its lowest value (<1% of control), the cells slowly acidified to reach a stable pHi of 6.92 after 50 min of MI. In the presence of EIPA (10 micromol/L), the pattern of changes in pHi was unchanged and acidification was not increased, indicating that the Na+/H+ exchangers were inactive during ATP depletion. When inorganic phosphate (P(i)) or Na+ was omitted from the apical solutions during MI, the transient alkalinization was no longer observed and the cytosol slowly acidified. Experiments on Na+-dependent alkalinizations revealed the presence of a Na-P(i) cotransporter in the apical cell membrane. With indirect immunofluorescence, the Na-P(i) cotransporter expressed in these primary cell cultures could be identified as Na-P(i) type I. Although the exact physiological role of Na-P(i) type I still is unresolved, these experiments demonstrate that apical Na-P(i) type I activity is increased at the onset of ATP depletion in MTAL cells.
Jans
F
F
Department of Physiology, Biomedical Research Institute, University of Hasselt, Diepenbeek, Belgium. frank.jans@hotmail.com
Ameloot
M
M
Wouters
P
P
Steels
P
P
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D019084:Fluorescent Antibody Technique, Indirect; D006863:Hydrogen-Ion Concentration; D007511:Ischemia / Q000378:metabolism; D007679:Kidney Medulla / Q000378:metabolism*; D008138:Loop of Henle / Q000378:metabolism*; D011817:Rabbits; D050609:Sodium-Phosphate Cotransporter Proteins, Type I / Q000502:physiology*
D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D000255:Adenosine Triphosphate