Substrate and inhibitor specificity of monocarboxylate transport
across the plasma membrane of single rat cardiac myocytes determined
using the intracellular ph-sensitive fluorescent indicator bcecf.
Wang, X., Levi, A. J. and Halestrap, A. P.
Departments of Biochemistry and Physiology, School of Medical
Sciences, University of Bristol, Bristol, BS8 1TD, UK
APStracts 2:0355H, 1995.
We have used the intracellular pH-sensitive fluorescent dye 2 , 7 -
bis (carboxyethyl)- 5 (6) - carboxyfluorescein (BCECF) to
characterise the substrate and inhibitor specificity of
monocarboxylate transport into isolated rat heart cells. Further
evidence was obtained for the presence of two lactate carriers
present in heart cells (Wang, X., et al., Biochem. J. 290:249-258,
1993) both distinct from the recently cloned monocarboxylate
transporter isoform 1 (MCT-1) found in many other cell types. Only
one isoform was potently inhibited by [alpha]-cyano-4
-hydroxycinnamate (CHC - Ki 190[mu]M) and the stilbene disulphonates
DIDS (Ki 79[mu]M) and DNDS (Ki of cis and trans isomers 38[mu]M and
171[mu]M respectively; neither isomer inhibits MCT-1). The second
carrier had a Ki of about 3mM for CHC and 0.5-2mM for the stilbene
disulphonates. Thus, unlike in many other tissues, in rat heart cells
these inhibitors are not effective at blocking lactate transport
totally unless used at very high concentrations. Both carriers were
inhibited by 3-isobutyl-1-methylxanthine (IBMX - Ki 340[mu]M) and
neither by 5-nitro-2-(3-phenylpropylamino) benzoate (NPPB, a potent
inhibitor of MCT-1). The overall Km and Vmax of transport of a
variety of substituted monocarboxylates (C2-C5) were determined,
although it was not possible to elucidate the kinetic parameters of
the two isoforms. Of physiological interest, the ketone bodies D
-[beta]-hydroxybutyrate and acetoacetate had Km values of 10mM and
5.4mM respectively. Vmax values were similar to those of L-lactate
and pyruvate and indicate that transport could limit rates of
utilisation of ketone bodies. No stereoselectivity for L- over D-
isomers of 2-chloro- or 2-hydroxy acids were observed
Received 7 December 1994; accepted in final form 7 August 1995.
APS Manuscript Number H1072-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 August 1995.