[Specific binding of organic acids by a fraction of the basolateral membrane of the rat kidney cortex isolated by osmotic shock].

Non-vesiculated membrane fragments of the basolateral membrane of the rat kidney cortex were isolated by the osmotic shock method and fractionated by means of differentional centrifugation. Formation and purity of membrane fragments were tested morphologically (contact luminescent, phase-contrast and electron microscopy) and biochemically (determination of the activity of marker enzymes--Na+, K+-dependent ATPase and alkaline phosphatase). The activities of Na+, K+-ATPase and alkaline phosphatase in the purified fraction of the basolateral membrane were 21 and 0.2%, respectively, of those in the kidney cortex homogenate. The binding of 14C-hyppuric and 14C-uric acids with basolateral membrane fragments was studied by means of filtration through the millipore filters. The existence of competitive inhibition and substrate saturation of the binding testify to the presence of organic acid carrier in the basolateral membrane. The affinity of the carrier to hyppurate in membrane preparations was proved to be the same as in the intact proximal tubules (the apparent Michaelis constant is equal to 0.7 mM). The equilibrium constant (Kf) for the carrier-hyppurate complex does not exceed 10 M-1. That means that the complex of the carrier with hyppurate is not strong.