1 7 2 s Biochemical Society Transactions ( 1 992) 20
Changes in the myocardial creatine kinase isozyme
profile with progression and regression of volume
overload eccentric hypertrophy
MARK L FIELD, CAMPBELL THOMPSON. CHRISTOPHER
HENDERSON', ANNE-MARIE L SEYMOUR" and GEORGE K. RADDA.
iron repletion, the M to B shift was found to revert to control
levels while the total activity was significantly reduced below that
of controls. The percentage of mitochondrial CK isozyme rose in
hypertrophy and dropped to normal in regression.
a) EIGHT WEEKS OF IRON DEFICIENCY
Department of Biochemistry, Oxford University, South Parks
Road, Oxford OX1 3QU, U.K.; Bioscience II, ICI Pharmaceuticals,
Alderley Park. Cheshire SKI0 4TG, U.K. and ** National Heart and
Lung Institute, London SW3 6LY. U.K.
Myocardial hypertrophy may be classified as either pressure
overload (PO) or volume overload (VO) depending on the nature of
the stimulus for growth [l]. PO hypertrophy results from an
elevated afterload leading to concentric growth, whereas VO arises
from an elevated preload leading to eccentric growth. The response
of the creatine kinase (CK) system to hypertrophy has been well
characterized in models of PO [2] as a decrease in cytosolic
phosphocreatine [PCr], total CK activity and the MM isozyme as
well as an increase in the MB & BB isozymes. The suggestion has
been made that although PO and VO hypertrophy are both the
result of alterations in haemodynamic load, they are biochemically distinct [l]. This raises the question whether the CK
response to VO is different to that in PO. Furthermore, are the
changes in the CK system reversible during regression of
hypertrophy? We have addressed these questions using a model
of chronic anaemia in the rat.
Ten 50g male Wistar rats were fed a diet deficient in iron (5-7
mgslkg) over a period of eight weeks. Five rats were then
randomly picked for examination while the remaining five were
placed back on a normal diet (iron contenbl09 mgskg) for a
further eight weeks. Age matched controls were used for
comparison. Hearts were excised and perfused in the Langendorff
mode at constant flow rate (1Omls min.-l g wet wt.-1). The
perfusate, Krebs-Henseleit buffer containing 1.25mM CaC12,
9mM glucose and 2mM pyruvate was gassed [02/C02 19:l
(Volume %)] and warmed to 37oC. 31P NMR spectroscopy was
performed in a vertical super wide bore (82mm) 7.05T
superconducting magnet at the Larmor frequency for phosphorus
of 121.5 MHz. Spectra were acquired using 900 pulses and a 15
second interpulse delay, after which hearts were freeze clamped
for biochemical analysis. Total CK activities and isozyme profile
were measured by the method of Rosalki et al [3] using a Gelman
CK reagent kit and fluorescence densitometry.
Eight weeks of anaemia resulted in a 30% (P<O.OOl) elevation
in heart wt./body wt. ratio (Tablel.). This hypertrophy was
completely reversible by 8 weeks of iron repletion. The myocardial phosphocreatine concentration was unchanged compared with
age and weight matched controls unlike models of PO (2.4).
However, cytosolic phosphocreatine was found to be elevated in
regression. Although there was an M to B foetal shift (Figurel).
total CK activity was increased in contrast to models of PO. Upon
Table I.Effects of iron deficiency (8 weeks)followed by iron repletion (8 weeks)
on the rat myocardium. Each value represents the mean S.E.M. of greater than
5 measurements. PCr= phosphocreatine. *=p<O.OS.usingthe Students t test
*
control
fed
control
fed
Bodywt.
(9)
206
lt3
209
f4
277
lt6
3 1 7'
+13
Heart wt./
bodywt.
(g/kg)
5.15
+0.2
7.39'
t0.5
4.13
to.1
t0.2
PCr (pmol
/g wet wt.)
5.33
t0.4
5.29
f0.4
5.63
f0.5
8.1 *
t0.5
CK activity
(IU)
259
+9
361
+9
297
f14
192'
f12
4.15
r
MlTO
MB
BB
b) EIGHT WEEKS OF IRON REPLETION
60
1
50
Y
0
- r 40
5s
a = 30
u
- m
0 2 0
*
m
control
fed
10
0
MlTO
MM
MB
BB
FIGURE 1. Effects of iron deficiency (8 weeks)foUowed by iron repletion (8
weeks)on (he rat myocardial creatine base (CK) isayme profileError bars
represent the mean +S.E.M.of >n=5 NS= not significant, *=p<o.O5 using the
Students t test.
During the hypertrophy of a myocyte, the contribution of the
phosphocreatine shuttle[5] to the supply of ATP may become
important because of increased diffusion distances between mitochondria and myofibrils. The effect of changes in the CK system on
the contribution of PCr to th6 supply of ATP as a result of the
foetal shift is unclear. Certainly during hypertrophic growth the
efficiency of the CK system will be compromised by a drop in the
Yo MM isozyme and any contribution to the supply of ATP by the
CK system would be limited. This may restrict the myocytes'
ability to sustain hypertrophic growth. The BB and MB isozyme
rise may be beneficial if spatially associated with the increased
glycolytic component [6] normally seen in hypertrophy.
Localisation of the hypertrophic induced B form, has yet to be
determined. Similarly, the increase in mitochondrial CK would
assist in the supply of ATP if a shuttle is in operation under these
conditions. The elevated total CK activity and normal cytosolic
phosphocreatine (neither characteristics of PO) may assist in
acute ischaemic episodes associated with hypertrophy. The net
result of the CK shift may be complicated by other isozyme shifts
such as myosin. The correction of these changes in regression
appears to involve an overshoot in the opposite direction. This
may be the result of the trial and error process of hypertrophic
adaption suggested by Swynghedauw[il. It is concluded that the net
effect of a CK foetal shift on the energy supply of the heart is
likely to depend on the type and extent of the hypertrophy.
The authors thank the MRC, ICI Pharmaceuticals and the BHF for
financial support.
1.
2.
Abbreviations used CKcreatine base; Po,pressure overload: VO. volume
overload.
MM
3.
4.
5.
6.
7.
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