[Passive Ca2+ influx into vesicles of the sarcoplasmic reticulum, modified by succinic anhydride].

Treatment of the sarcoplasmic reticulum (SR) vesicles with succinic anhydride in concentration of 1-2 mM modifies about 20% of amino groups. It increases initial rate and changes the pH-dependence of the passive influx of Ca2+ into vesicles and does not affect either Ca(2+)-binding or maximal passive Ca(2+)-loading of the SR vesicles. It is supposed that this effect may be caused by modification of the Ca-channel gating behaviour as a result of replacement of positive surface amino groups by carboxyl groups.

[Change in the passive influx of Ca2+ into sarcoplasmic reticulum vesicles as a result of chemical modification of surface amino groups].

Treatment of sarcoplasmic reticulum (SR) vesicles with trinitrobenzene (TNBS) and 1-ethyl-3(3-dimethylaminopropyl)carbodiimide (EDC) stimulates the initial rate of passive influx of Ca2+ into SR vesicles, but does not affect either the binding or the maximal passive loading of SR vesicles with Ca2+. The changes in the kinetics of KCl-stimulated passive influx of Ca2+ depend on the reagent used. It is supposed that stimulation of passive influx of Ca2+ into SR vesicles and the changes in the reaction kinetics may be caused by modification of the Ca2+ channel gating behaviour as a result of binding of surface amino groups.

[The effect of pH on the passive transport of Ca2+ by membranes of fragmented sarcoplasmic reticulum of skeletal muscles].

The initial rate of Ca2+ translocation in vesicular preparations of the sarcoplasmic reticulum membranes is shown to fall with a pH decrease to 6.0 or 5.0 and to rise with a pH change to 7.

[Ca 2+ outflow from sarcoplasmic reticulum vesicles during changes in membrane potential, Ca2+ concentration and pH].

The concentration gradient Ca2+ outflux from the vesicles of the fragmented sarcoplasmic reticulum of rabbit skeletal muscles has been studied under conditions of the induced membrane potential, the concentrations of Ca2+ and H+ in the medium washing over the vesicles being different. The Ca2+ outflux from vesicles is shown to be the same with a decrease of the membrane potential from--80 down to -10 mV and gets higher with the zero and subsequent positive values of the latter. A significant intensification of the Ca2+ outflux from vesicles under the effect of external-vesicular Ca2+ has been observed at its concentration of 10(-5) M.