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1 Department of Medicine
(Cardiology) and 2 Ernest Gallo
Clinic and Research Center,
Long-standing heavy alcohol consumption acts as
a chronic stress on the heart. It is thought that alcohol-induced
changes of contractility are due to altered
Ca2+ handling, but no measurements
of cytosolic Ca2+
([Ca2+]c)
after chronic alcohol exposure have been made. Therefore experiments were performed to determine whether alcohol-induced changes in contractility are due to altered
Ca2+ handling by measuring
[Ca2+]c
(indo 1) in hearts from rats drinking 36% ethanol for 7 mo and
age-matched controls. Peak left ventricular pressure was depressed (
16%), whereas rates of contraction (12%) and relaxation
(14-20%) were faster in alcohol-exposed hearts. Systolic
[Ca2+]c
(808 ± 45 vs. 813 ± 45 nM), diastolic
[Ca2+]c
(195 ± 11 vs. 193 ± 10 nM), and rates of
[Ca2+]c
rise and decline were the same in alcohol-exposed and control hearts.
Protein levels of Ca2+-handling
proteins, sarcoplasmic reticulum
Ca2+-ATPase and phospholamban,
were the same in myocytes isolated from alcohol-exposed and control
hearts (SDS-polyacrylamide gel). These data suggest that chronic
alcohol-induced contractile changes are not due to altered
Ca2+ handling but may be due to
changes at the level of the myofilament. As a first step in elucidating
the mechanism(s) of alcohol-induced changes at the myofilament, we
assessed myosin heavy chain (MHC) isoform content (SDS-polyacrylamide
gel).
-MHC was decreased relative to
-MHC
(a/a + b = 0.55 ± 0.03 vs. 0.66 ± 0.02; P < 0.02) in alcohol-exposed
hearts, which cannot account for the observed alcohol-induced
contractile changes. In conclusion, changes of myocardial contractility
due to chronic alcohol exposure do not result from altered
Ca2+ handling but from changes at
the level of the myofilament that do not involve MHC isoform shifts.
ethanol; myocyte; myosin heavy chain; sarcoplasmic reticulum; adenosinetriphosphatase; phospholamban
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