[Efflux of Ca2+ from fragmented sarcoplasmic reticulum during AMP deamination]

Deamination of AMP in skeletal muscle sarcoplasmic reticulum followed by an increase in pH from 6,5 up to 8,0 leads in a liberation of part of Ca2+ from the SR vesicles. This effect is enhanced by K+, which activate the deamination, and is suppressed by Mg2+, which inhibit the reaction. The activating effect of AMP on Ca2+ efflux from the vesicles markedly decreases after AMP deaminase dissociation from the vesicles and is restored after reconstitution of their deaminase activity. Substitution of IMP for AMP causes a decrease of Ca2+ efflux from the vesicles. The data obtained are in good agreement with the assumption that the ammonium formation from AMP can favour the release of Ca2+ from some vesicles of SR.