Phosphate transport in kidneys: effect of transmembrane electrical potential.
The effect of a transmembrane electrical potential on phosphate transport by kidney brush-border membrane vesicles was studied. The initial rate of Na(+)-dependent phosphate influx was twice as high as that of efflux. Generation of a negative transmembrane potential had a stimulatory effect on the rate of influx but had no effect on efflux. The Na+ saturation curve for phosphate influx was sigmoidal, and the Hill coefficients were similar, in the presence and absence of a transmembrane potential. The membrane potential increased both the affinity for phosphate and the maximal velocity (Vmax) of the transporter. In the absence of a Na+ gradient, the stimulation by the potential was 1.78-fold. When a proton gradient (in greater than out) was the driving force, the electrical potential stimulated phosphate transport 1.71-fold. Internal Na+ (trans) inhibited phosphate influx whether a potential was present or not. Internal phosphate (trans) stimulated phosphate influx in the absence of a potential but not in its presence. These results indicate that the electrical potential is an important driving force for the Na(+)-phosphate carrier and that the translocation of the carrier is a potential-dependent step.
Université du Québec à Montréal, Département de Chimie, Canada.
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Béliveau
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Strévey
D000818:Animals; D001692:Biological Transport; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D004058:Diffusion; D004563:Electrochemistry; D005947:Glucose / Q000493:pharmacokinetics; D007668:Kidney / Q000378:metabolism* / Q000502:physiology; D007700:Kinetics; D008297:Male; D010710:Phosphates / Q000493:pharmacokinetics*; D051381:Rats; D011919:Rats, Inbred Strains; D012044:Regression Analysis; D012964:Sodium / Q000494:pharmacology; D013237:Stereoisomerism
D002712:Chlorides; D010710:Phosphates; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012964:Sodium; D005947:Glucose