Аннотация
Studies are presented that relate the calcium binding of isolated
sarcolemmal membranes to myocardial contractility. The contractile
strength of the perfused rabbit interventricular septum as a function
of perfusate calcium concentration is compared with calcium bound
to isolated rabbit sarcolemma at the same calcium concentrations.
If the calcium-binding incubation medium contains 140 mM sodium chloride,
the shapes of these two curves are identical. In another experiment,
sarcolemmal calcium-binding data are compared with the results of
Tillisch et al. (J. Mol. Cell. Cardiol. 11:137-148, 1979), who studied
the response of rabbit papillary muscles to changes in the perfusate
sodium concentration. Again a positive correlation between calcium
bound and force developed is obtained. The results of experiments,
using the isotope 22Na on the binding of sodium to isolated sarcolemmal
membranes were subjected to Scatchard analysis. This revealed a single
type of sodium receptor. The affinity constant for sodium binding
is 110 M-1 and calcium appears to behave as a competitive inhibitor
of sodium binding. The experimental results strongly imply a quantitative
relationship between sarcolemmal calcium binding and myocardial contractility.
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