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Division of Cardiology, Department of Pediatrics, University of Washington School of Medicine and Children's Hospital and Medical Center, Seattle, Washington 98195-6320
Changes in the
relationship between myocardial high-energy phosphates and oxygen
consumption in vivo occur during development, implying that the mode of
respiratory control undergoes maturation. We hypothesized that these
maturational changes in sheep heart are paralleled by alterations in
the adenine nucleotide translocator (ANT), which are in turn related to
changes in the expression of this gene. Increases in myocardial oxygen
consumption (M
O2) were
induced by epinephrine infusion in newborn (0-32 h,
n = 6) and mature sheep (30-32
days, n = 6), and high-energy
phosphates were monitored with 31P
nuclear magnetic resonance. Western blot analyses for the
ANT1 and the
-subunit of
F1-adenosinetriphosphatase
(ATPase) were performed in these hearts and additional
(n = 9 total per group) as well as in
fetal hearts (130-132 days of gestation,
n = 5). Northern blot analyses were
performed to assess for changes in steady-state RNA transcripts for
these two genes. Kinetic analyses for the
31P spectra data revealed that the
ADP-M
O2 relationship for
the newborns conformed to a Michaelis-Menten model but that the mature data did not conform to first- or second-order kinetic control of
respiration through ANT. Maturation from fetal to mature was accompanied by a 2.5-fold increase in ANT protein (by Western blot),
with no detectable change in
-F1-ATPase. Northern blot data
show that steady-state mRNA levels for ANT and
-F1-ATPase increased
~2.5-fold from fetal to mature. These data indicate that
1) respiratory control pattern in
the newborn is consistent with a kinetic type regulation through ANT,
2) maturational decreases in control
through ANT are paralleled by specific increases in ANT content, and
3) regulation of these changes in
ANT may be related to increases in steady-state transcript levels for
its gene.
myocardial oxygen consumption; mitochondria; sheep; adenosine 5'-triphosphate; adenosinetriphosphatase; oxidative phosphorylation
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