Influence of extracellular pH and perfusion rate on Na+/H+ exchange in cultured opossum kidney cells.
Studies were undertaken in cultured opossum kidney (OK) cells to determine whether the rate of H+ secretion by apical membrane Na+/H+ exchange is modulated by changes in extracellular pH or perfusion rate. H+ secretion was assessed in single cells by measuring the rate of Na(+)-dependent intracellular pH recovery after NH4Cl loading, using the pH-sensitive fluorescent dye, 2'7'-bis(carboxyethyl)-5,6-carboxyfluorescein, in monolayers mounted to allow independent perfusion of the apical and basolateral surfaces. At constant intracellular pH, Na(+)-dependent H+ secretion was found to be inversely related to extracellular H+ activity, and directly related to the perfusate flow rate. Inhibition of H+ secretion by perfusate acidity occurred immediately and was greater when perfusate Na+ was reduced, consistent with H+ competition with Na+ for binding to the transporter. By contrast, the effect of the perfusion rate was a delayed response, requiring 20 min of exposure, and was independent of perfusate Na+ concentration. The results indicate that both extracellular pH and the perfusion rate modulate H+ secretion by OK cells, and that the two effects are independent.
Gennari
F J
FJ
University of Vermont, Burlington 05405.
Helmle-Kolb
C
C
Murer
H
H
D000818:Animals; D002021:Buffers; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D005110:Extracellular Space / Q000502:physiology*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D007700:Kinetics; D009893:Opossums; D010477:Perfusion; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D002021:Buffers; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D006859:Hydrogen; D012964:Sodium