[Kinetic analysis of mechanisms of Na+-dependent organic acid transport in the proximal tubules of surviving frog kidney. II. Relationship between Na+ concentration in the medium and changes in the parameters of the Michaelis-Menten equation for fluorescein and uranin transport].
The dependence of active transport rates of fluorescein and uranin into proximal tubules was studied, firstly, on the concentration of these substrates in the incubation medium with constant Na-concentration and, secondly, on Na+-concentration in the medium with constant concentrations of fluorescein or uranin, Km, Vmax, and KmNa, VmaxNa values being determined correspondingly. With the decrease of Na+-concentration in the medium the apparent Km values for fluorescein and uranin increase, while Vmax values remain unchanged and ratios Vmax/Km decrease. The 1/Km value for uranin transport is a linear function of Na+-concentration, while it is a quadratic function of Na+-concentration for fluorescein transport. The KmNa value for fluorescein transport is twice as much as that for uranin transport. The obtained data suggest that one Na+-ion is spent from the medium for translocation of one uranin molecule across the basal membrane, whereas two Na+-ions from the medium are necessary for translocation of one fluorescein molecule. It is assumed that fluorescein and uranin transports are carried out by producing a four-fold transporting complex (a carrier+a substratum+2Na+; in the case of fluorescein 2Na+ appear from the medium, whereas in the case of uranin only one Na+ from the medium is used.
D000818:Animals; D001001:Anura; D001693:Biological Transport, Active / Q000187:drug effects; D005452:Fluoresceins / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D012964:Sodium / Q000494:pharmacology*
D005452:Fluoresceins; D012964:Sodium
Kineticheskiĭ analiz mekhanizmov Na+-zavisimogo transporta organicheskikh kislot v proksimal'nykh kanal'tsakh perezhivaiushcheĭ pochki liagushki. II. Izmeneniia parametrov uravneniia Mikhaélisa--Mentena dlia transporta fluorestseina i uranina v zavisimosti ot kontsentratsii Na+ v srede.