Relationship between parvalbumin content and the speed of relaxation in chronically stimulated rabbit fast-twitch muscle.
The time courses of changes in parvalbumin (PA) content, isometric twitch tension, and half-relaxation time (1/2 RT) were studied in rabbit 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 Ca2+-uptake by the SR (Leberer et al. 1987). While prolonged stimulation produced no further decrease in the Ca2+-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 mammalian fast-twitch muscle.
Klug
G A
GA
Fakultät für Biologie, Universität Konstanz, Federal Republic of Germany.
Leberer
E
E
Leisner
E
E
Simoneau
J A
JA
Pette
D
D
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000502:physiology*; D009126:Muscle Relaxation; D009132:Muscles / Q000502:physiology*; D010320:Parvalbumins / Q000502:physiology*; D011817:Rabbits; D012016:Reference Values; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013997:Time Factors
D009124:Muscle Proteins; D010320:Parvalbumins; D002118:Calcium