SCN CONTRACTURE IN SKELETAL MUSCLE

Abstract

If a Ringer''s solution, containing NaSCN in a concentration which is below the threshold for direct contracture, is allowed to bathe the frog sartorius muscle for a definite time, and is then replaced by Ringer''s solution, a contracture takes place which is called indirect contracture because of its occurrence in pure Ringer''s solution. This indirect contracture can be obtained also by application of other SCN salts such as Ca(SCN)2 and NH4SCN. This and the observed low value of the isometric tension show that the indirect contracture is a SCN-contracture. The strength of the indirect SCN-contracture depends chiefly upon the composition of the 2nd solution which is substituted for SCN-Ringer''s solution. It is much greater in NaCl than in Ringer''s solution, and by the addition of small amounts of Ca, Sr, or Mg or still lower con-centrations of heavy metals such as Cu, Co, and Fe, indirect contracture can be suppressed completely. It increases with decreasing osmotic pressure and increasing pH. It is favored by stimulation of the muscle with condensor discharges. The assumption that the strength of indirect contracture is determined by the velocity with which NaSCN leaves the muscle cell and therefore by the permeability of the muscle easily explains these facts because ions increase and decrease indirect contracture in the same sense as they influence permeability. There is but 1 exception: BaCl2 if added to the 2nd solution increases the strength of indirect contracture.