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Double dependence of organic acid active transport in proximal tubules of surviving frog kidney on sodium ions II. Relationship between counter-flows of fluorescein and sodium ion across cell layer

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

10.1016/0005-2736(77)90154-7

1879-2642

A.A. Nikiforov, Vladimir Bresler,

Ion Transport and Channel Regulation

With the aid of a direct microfluorimetric method a dependence of organic onion (fluorescein) transport into proximal tubules of surviving frog kidney on Na+-flow in the opposite direction was studied. It was shown that the complete removal of Na+ from the tubules lumen resulted in inhibition of fluorescein transport of about 30%. After a specific inhibitor of sodium channels, amiloride (10-3M) having been introduced into lumen of the tubules, the fluorescein transport was inhibited to the same extent. Amiloride affects only when Na+ is present in the tubular lumen. S present in the tubular lumen. Strophantin K (5 · 10−5 M), a specific inhibitor of (Na+, K+)-ATPase, reduced fluorescein transport about twice. Substances increasing the 3′,5′-AMP level in cells (theophylline, NaF) and exogenous 3′,5′-AMP inhibited fluorescein transport while substance that decreased the 3′,5′-AMP level intracellularly (carbachol) stimulated it. For realization of these effects Na+ should be present in proximal tubules lumen. Thus, the various effects on the Na+ flow from lumen of the tubules to medium at the level of both the basal and apical membranes alter the rate of organic acid active transport from medium to lumen as a result of changes in the maximum rate of transport (V) with unchanged Km. It is suggested that the system of Na+ extrusion from proximal tubules produces peritubular membrane-side (near the membrane) gradient of Na+ concentration which may be higher than the summary Na+ gradient between the medium and the cytoplasm. The magnitude of this gradient affects the maximal rate value of Na+-dependent organic acid transport. So, there is a double dependence of the active transport system on Na+, and the stages where Na+ is needed are: (1) the formation of a carrier-substrate-Na+ complex and (2) the production of substantial membrane-side Na+ gradient at the expense of Na+ extrusion from the tubules.