Portal de Periódicos da CAPES

Double dependence of organic acid active transport in proximal tubules of surviving frog kidney on sodium ions I. Influence of sodium ions in bath medium on the uptake and run out of fluorescein and uranin

1977; Elsevier BV; Volume: 468; Issue: 1 Linguagem: Inglês

10.1016/0005-2736(77)90153-5

1879-2642

Vladimir Bresler, A.A. Nikoforov,

Pediatric Urology and Nephrology Studies

With the aid of direct microfluorimetric determination of marker organic anions (fluorescein and uranin) accumulated in the proximal tubules the influence of Na+ in the bath medium on the active transport of these anions was studied. Kinetic analysis of the rate dependence of organic acid active transport into tubules on their concentration in the bath medium with a constant Na+ concentration permitted to define values of apparent Km and V for uranin and fluorescein transport in the medium with different Na+ content. It was shown that a decrease of Na+ concentration in the medium increases Km and lowers the V/Km ratio with uncharged V. By varying the Na+ concentration in the medium with a constant concentration of the marker anion the KmNa+ and VNa+ values for fluorescein and uranin transport were determined. A KmNa+ value for fluorescein in twice as much that for uranin. The 1/Km value for uranin transport is a linear function of Na+ concentration, while for fluorescein transport it is a quadratic one. Therefore it is concluded that two Na+ from the medium participate in active transfer of one fluorescein anion whereas only one Na+ from the medium is required for active transfer of one uranin anion. The run out of fluorescein from tubules preloaded with this acid is sharply reinforced by the Na+ omission from the medium. Thus, active transport of organic acids in proximal tubules of frog kidney is Na+-dependent, and Na+ from the medium is likely to participate directly in formation of a transport complex. When Na+ is absent in the medium a carrier fulfils a facilitated diffusion only.