AJP - Cell Physiology, Vol 255, Issue 2 C133-C139, Copyright © 1988 by American Physiological Society
Transport of 3-hydroxy[3-14C]butyrate by dissociated cells from rat brain
J. T. Tildon and L. M. Roeder
Department of Pediatrics, University of Maryland School of Medicine, Baltimore 21201.
Recent studies suggest that the utilization of oxidizable substrates by the
brain may be regulated in part by transport across the plasma membrane.
Dissociated brain cells obtained by mechanical disruption of rat brain were
used to measure the uptake of 3-hydroxy[3-14C]butyrate. Total uptake
revealed two mechanisms (diffusion and a carrier-mediated system). A
Lineweaver-Burk plot of the latter component yielded an apparent Km of 1.47
mM and a maximal velocity (Vmax) of 5 nmol.min-1.mg protein-1. The rates of
uptake were temperature dependent and were significantly higher at pH 6.2
than at pH 7.4 or 8.2. Preloading the cells and increasing the
intracellular concentration of 3-hydroxybutyrate using 12.5 and 25 mM
increased the rate of uptake 143 and 206%, respectively, indicative of an
accelerative exchange mechanism. Uptake was inhibited approximately 50% by
(in mM) 10 phenylpyruvate, 10 alpha-ketoisocaproate, 10 KCN, and 1.5
NaAsO2. Uptake was also decreased by (in mM) 5 lactate, 5 methyl malonic
acid, 1 alpha-cyano-4-hydroxycinnamate, and 1 mersalyl. Dissociated brain
cells from 14- to 16-day-old rats accumulated 3-hydroxybutyrate at a rate
more than two-fold greater than cells from either younger (2-day-old) or
older (28-day-old and adult) animals. These data are consistent with the
proposal that 3-hydroxybutyrate is taken up by the brain by both diffusion
and a carrier-mediated transport system, and they support the hypothesis
that transport at the cellular level contributes to the regulation of
substrate utilization by the brain.
