CONDITIONS CAUSING A CONTINUOUS INCREASE IN Ca⁺⁺ DISSOCIATION FROM THE MUSCLE FIBRES

Abstract

1) ⁴⁵Ca efflux from the isolated frog sartorius is usually characterized by a transient increase in it when some factors to increase membrane permeability have been applied to the muscles. Occasionally, the ⁴⁵Ca efflux increase becomes continuous. The intracellular ionic properties which are common to the conditions for a continuous increase in ⁴⁵Ca efflux have been investigated with special reference to the behavior of Ca ions.2) Although when Ca free Ringer and high K Ringer were successively, but independently, applied to the muscles ⁴⁵Ca efflux from the tissue showed a transient increase in response to the treatment with each solution, the ⁴⁵Ca efflux was accompanied with a continuous increase when both conditions were simultaneously applied to the muscles. Combination of trypsin and ouabain caused a continuous increase in ⁴⁵Ca efflux. The treatment with Ca free Ringer containing Sr, Mg or Ni at the concentrations which could not prevent the appearance of a transient increase in ⁴⁵Ca efflux producible by Ca free Ringer also resulted in a continuous increase of ⁴⁵Ca efflux. In a similar situation, Ba and Cu ions could not demonstrate such a change.3) The conditions to generate a continuous increase in ⁴⁵Ca efflux from the muscle are supposed to be the factors which cause a rise of intracellular Ca⁺⁺ concentration simultaneously with mobilization of membrane Ca⁺⁺. The former change is probably brought about by influencing upon the activity of the sarcotubular system. When the latter process is conspicuous ⁴⁵Ca efflux increase may be transient in nature.