Transport and metabolism of l-glutamate during oxygenation, anoxia
and reoxygenation of rat cardiac myocytes.
Dinkelborg, Ludger M., Rolf K. H. Kinne, and Manfred K. Grieshaber.
INSTITUT F[umlaut]uR ZOOPHYSIOLOGIE, LEHRSTUHL F[umlaut]uR
STOFFWECHSELPHYSIOLOGIE, HEINRICH-HEINE-UNIVERSIT[umlaut]aT, 40225
D[umlaut]uSSELDORF AND MAX-PLANCK INSTITUT F[umlaut]uR MOLEKULARE
PHYSIOLOGIE, 44026 DORTMUND, GERMANY
APStracts 2:0508H, 1995.
The intracellular glutamate concentration of oxygenated isolated adult
rat heart cells incuba ted with 0.15 mmol x l-1 glutamate amounts to
2.89 +/- 0.6 mmol x l-1. Under these conditions the velocity of
glutamate transport was 24.3 +/- 1.6 pmol x min-1 x mg-1 protein and
occurs via a high affinity carrier characterized by an apparent
affinity (Km) value of 0.18 +/- 0.03 mmol x l-1. At high glutamate
concentrations (>1 mmol x l-1) this high affinity transport
system is superimposed by additional uptake processes of a low
affinity but a high capacity for glutamate. The 1.6-fold increased
uptake of glutamate observed during 30 min of anoxic incubation of
cardiomyocytes does not prevent an intracellular decrease in this
amino acid to a concentration of 0.49 mmol x l-1. After 15 min
reoxygenation of cardiomyocytes the in tracellular glutamate content
increases to the control values of oxygenated cells. Only 2.4 % of
the glutamate increase after reoxygenation is due to the transport of
glutamate from the incubation medium. The competitive inhibitor of
transaminases, aminooxyacetate, prevents both the observed
intracellular decrease in glutamate during anoxia and the increase in
intracellular glutamate after reoxygenation of cardiomyocytes. Half
of the amino groups needed for the synthesis of glutamate originate
from intracellular alanine which increases during anoxia and is
metabolized during reoxygenation of cardiomyocytes. The velocity of
the glutamate uptake of cardiomyocytes incubated in a medium
containing 10 mmol x l-1 L-glutamate amounted to 728 +/- 140 pmol x
min-1 x mg-1 protein. During anoxic incubation of cardiomyocytes at
this high extracellular glutamate concentration the observed
intracellular glutamate decrease is compensated by a simultaneous
uptake of this amino acid via the trans port processes characterized
by a high capacity.
Received 16 May 1995; accepted in final form 6 November 1995.
APS Manuscript Number H462-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95