Functional characterization of albumin binding to the apical
membrane of ok cells.
Gekle, Michael, Sigrid Mildenberger, Ruth Freudinger, and Stefan
Silbernagl.
Department of Physiology, University of W[umlaut]urzburg,
W[umlaut]urzburg, Germany
APStracts 3:0041F, 1996.
We characterized binding of albumin to the apical membrane of OK cells
using FITC-(bovine serum)albumin as substrate. Functional analysis of
binding data showed one specific binding site characterized by half
-maximal binding (Km) at 20 mg/l (300 nmol/l) and maximal binding
capacity (Bmax) of 0.61 [mu]g/mg cellular protein. Excess of
unlabeled albumin (BSA) inhibited binding at low concentrations of
FITC-albumin completely but only partially at high concentrations.
FITC-albumin binding was reversible and pH-dependent. Km increased
about 6-fold when pH decreased from 7.4 to 5.0. The inhibitory
effects of conalbumin, [alpha]-lactalbumin and transferrin were
significantly smaller as compared to BSA. We conclude that OK cells
express a high-affinity binding site for albumin on the apical
membrane. This binding site is pH-sensitive, binds albumin in the
physiological range and could be responsible for the effective
receptor-mediated reabsorption of albumin in the proximal tubule.
Received 10 October 1995; accepted in final form 22 February
1996.
APS Manuscript Number F337-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96