[Interrelated effects of ATP and ionic strength on Ca2+-sensitivity of isolated myofibrils].

Ability of isolated myofibrils for relaxation was studied in a medium with KCl concentrations of 6 to 250 mM with ATP content varying from 0.01 to 1.0 mM. It was shown that myofibrils can relax at all the studied values of the ionic strength, but ATP concentration required for the relaxation is to increase with decreasing the ionic strength A stable state of Ca2+-sensitive system of myofibrils is maintained at approximately the same values of ATP and KCl concentrations. A possible mechanism of this phenomenon is discussed.