Anions and the contraction of glycerol-extracted muscle fibers.

Glycerinated rabbit psoas fibers 5-19 days old were immersed in contracting solutions with and without varying concentrations of different sodium salts. Raising the pH of the solution in small steps identified a threshold pH above which the fibers rapidly developed maximum tension. In solutions with added chloride or acetate (O-O.15 M), threshold pH and maximum tension changed only slightly. In solutions with added nitrate, bromide, or iodide, fibers developed much less tension, according to the series: CH&OO> Cl> NOa> Br> I-. Addition of excess calcium to the last solutions produced no further tension. After 15 min in NO,, Br-, or Isolution, fibers partially regained tension when reimmersed in acetate but not chloride solution. Fibers that had developed tension in chloride solution lost some of it when reimmersed in nitrate, bromide, or iodide solution, according to the same anion series, out they retained more tension than they could develop initially in the latter solution.