Relationship between XXXX content and the speed of relaxation in chronically stimulated @entity95 fast-twitch muscle.

@entity141 @entity50808 @entity1 @entity95
The time courses of changes in @entity50808 (PA) content, isometric twitch tension, and half-relaxation time (1/2 RT) were studied in @entity95 tibialis anterior muscle following chronic 10 Hz nerve stimulation of 1-21 days. Up to 5 days stimulation had no effect on PA content, but it induced a slight (10-15%) increase in the 1/2 RT. This change occurred together with the previously observed 50% decrease in @entity141 -uptake by the SR (Leberer et al. 1987). While prolonged stimulation produced no further decrease in the @entity141 -uptake by the SR, PA content declined after 5 days of stimulation. The reduction in PA content was accompanied by a progressive lengthening of the 1/2 RT. However, the increase in 1/2 RT was particularly pronounced after PA had fallen below 50% of its normal value. A 90% reduction in PA coincided with a 60% increase in the 1/2 RT. By this time the staircase phenomenon, normally observed in fast-twitch muscle, was completely abolished. Although the changes in PA content and 1/2 RT were not linearly related, these results suggest that PA plays an important role in the relaxation process of @entity1 fast-twitch muscle.
