SALBUTAMOL AND CHRONIC LOW-FREQUENCY STIMULATION OF CANINE SKELETAL-MUSCLE

1. The effect of simultaneous application of chronic muscle stimulatio n and salbutamol on the expression of mRNAs and proteins normally expr essed by fast- or slow-twitch fibres was followed and the effects of c hanges in protein expression on mechanical performance were evaluated. Chronic low-frequency stimulation increased the myosin heavy chain (H C)-I level in the canine latissimus dorsi muscle and simultaneous admi nistration of salbutamol partially blocked this change. Associated wit h tile increase in HC-I level was a decrease in the velocity of shorte ning at zero load, V-max. The change in V-max was partially blocked by salbutamol. 2. Chronic low-frequency stimulation increased the levels of slow-twitch cardiac isoform sarco-/endoplasmic reticulum Ca2+-ATPa se (SERCA2a) and phospholamban mRNA, and SERCA2a and phospholamban pro tein expression. These changes were associated with an increase in tim e-to-peak tension and a decrease in fusion frequency. Simultaneous adm inistration of salbutamol blocked these changes in protein expression and muscle mechanics. Chronic stimulation of latissimus dorsi decrease d the levels of the fast-twitch isoform of sarco-/endoplasmic reticulu m Ca2+-ATPase (SERCA1a) and increased SERCA2a protein expression and d ecreased calcium uptake rate by muscle homogenates. These changes mere blocked by salbutamol. 3. The loss of latissimus dorsi muscle weight Ly chronic stimulation was partially blocked by salbutamol.