The effect of ions and buffers in acid preincubation solution on the myofibrillar ATPase stain of the rat plantaris muscle was examined. The time course of the activation of type I fibers and inactivation of type II fibers varied depending on the species and concentration of ions and buffers. A good discrimination between fiber types was produced with a combination of ions and buffers where the activation of type I fibers and inactivation of type IIA fibers were completed in less than five minutes. Muscle fiber types were clearly identified with the preincubation solution of 100mM citrate (pH4.55〜4.60) in which no neutral salts were added. 100mM succinate or the combination of 100mM acetate and 100mM KCl was also acceptable.
　We speculated that ions and buffers bound directly to myofibrillar protein with different strengths and thereby altered the rate of activation and inactivation of myofibrillar ATPase in a varied degree.

DESCENTE SPORTS SCIENCE Vol.7/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE