AJP - Cell Physiology, Vol 260, Issue 6 C1151-C1157, Copyright © 1991 by American Physiological Society
Sodium-dependent succinate transport by isolated chick intestinal cells
G. A. Kimmich, J. Randles and E. Bennett
Department of Biochemistry, School of Medicine and Dentistry, University of Rochester, New York 14642.
Isolated chick intestinal epithelial cells take up succinate by a
Na(+)-coupled transport system similar in some characteristics to those
described for renal epithelium. The transport system exhibits a hyperbolic
dependence on succinate concentration but a sigmoidal dependence on Na+
concentration. Best nonlinear fit of the Na+ dependence data to the Hill
equation indicates a Michaelis constant for half-maximal transport rate
(Km) for Na+ of approximately 20 mM, a maximal transport rate (Vmax) of 1.1
nmol succinate.min-1.mg protein-1, and a Hill coefficient of 2.5. Nearly
equivalent fit was obtained with trial Hill coefficients down to 2.0. The
data for succinate dependence indicated a Km of 25 microM and Vmax of 1.05
nmol.min-1.mg protein-1. The kinetic parameters indicate a higher affinity,
lower capacity system than for succinate transport in the renal
brush-border system. Thiocyanate-induced diffusion potentials cause no
change in Na(+)-dependent succinate influx despite pronounced effects on
the influx of tetraphenylphosphonium and on Na(+)-dependent
alpha-methylglucoside (AMG) and alanine uptake. Several other dicarboxylic
and tricarboxylic metabolic intermediates (but not the dicarboxylic amino
acids) compete with succinate for uptake via the transport system. The data
are consistent with the likelihood that these cells have a succinate
transport system with a 2Na+:1succinate stoichiometry per transport cycle.
The system catalyzes no net charge transfer and is therefore different from
the potential-responsive succinate transporter described for renal tissue.
