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심장근 근장그물에서의 Ca++과 Na+에 의한 Ca++유리작용 : The Ca*-and Nat-Induced Ca" Release from Isolated Cardiac Sarcoplasmic Reticulum

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김해원; 김명석; 박찬웅

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서울대학교 의과대학
Seoul J Med, Vol.23 No.1, pp. 7-16
The Ca't-and Nat-induced Ca" release was studied
in sarcoplasmic reticulum isolated from porcine ventricles
by milipore filtration method using radioisot·
ope "sCa.
The isolated cardiac sarcoplasmic reticulum took
up calcium maximally 40 to 50 min of incubation in
the presence of 50mM inorganic phosphate. After
reaching the maximal uptake, the spontaneous release
of calcium was observed at high concentrations of
CaCI, (above l50"M) in the medium, at the low
concentrations of CaC!" however, the amount of
calcium taken up was retained for prolonged period.
Unidirectional calcium efflux, calulated from mea'
surements of influx of tracer 4fiCa at steady state
calcium uptake, was stimulated by increasing external
remaining calcium concentrations in the range of
1 to 201,M. The initial calcium efflux showed saturation
kinetics with the apparent KCa uf 7/,M and a
maximal calcium efflux of 180 nmol of calcium/mg
In the absence of fiDmM inorganic phosphate, rna'
ximal calcium binding by isolated cardiac sarcoplasmic
reticulum in the free calcium concentrations
of 5 x 10-8 to 5 x 1O-5M was 40 nmol/mg protein.
Calcium release was not observed by 1 to 10mM
Na" in the medium containing 0.5mM EGTA to
prevent sarcoplasmic reticulum from rebinding the
released Caito
Tbe changes in Na'/K+ ratio also did not influence
the calcium binding or release.
From the experiment, the Ca"-induced Ca" release
from cardiac sarcoplasmic reticulum may be one of
the calcium release mechanisms, and the released Ca" could initiate the cardiac contraction In the physiclogic
conditions. The NaI itself and changes in Na"
/K I ratio might he no influence on calcium hinding
and release mechanism in cardiac sarcoplasmic reticulum.
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