Neural stimulation increased phosphate content of the P-light chain in fast-twitch white muscle in a frequency-dependent manner, with lesser effects in fast-twitch red and slow-twitch muscles.
The physiological consequences of P-light chain phosphorylation, including isometric twitch tension potentiation, are most prominent in fast-twitch white skeletal muscle due to higher kinase and lower phosphatase activities.
The physiological properties of contraction-induced phosphate incorporation into the phosphorylatable light chain (P-light chain) of myosin were examined in fast-twitch white, fast-twitch red, and slow-twitch skeletal muscles in situ. Neural stimulation of rat gastrocnemius muscles between 0.5 and 100 Hz produced an increase in the phosphate content of the P-light chain from the white portion of the muscle, and the rate of P-light chain phosphorylation was frequency dependent. The extent of phosphorylation of P-light chain from the fast-twitch red portion of the gastrocnemius muscle was less. In contrast to fast-twitch skeletal muscle, only high-frequency stimulation (30-100 Hz) produced a small increase in the phosphate content of P-light chain from the slow-twitch soleus muscle. Fast white muscle contained 2.2 and 3.5 times more myosin light chain kinase activity than did the fast red and slow muscle, respectively. The rate of P-light chain dephosphorylation was four times faster in slow muscle than in fast white muscle. Thus the greater extent of phosphorylation of P-light chain in fast-twitch white skeletal muscle fibers may be due in part to the presence of more kinase and less phosphatase activities. Isometric twitch tension potentiation was correlated to the extent of phosphorylation of P-light chain from fast white muscle. The physiological consequences of P-light chain phosphorylation are likely to be of greatest importance in fast-twitch white muscle.
Moore et al. (Thu,) reported a other. Neural stimulation vs. Different muscle types (fast-twitch white, fast-twitch red, slow-twitch) was evaluated on Phosphate incorporation into the phosphorylatable light chain of myosin. Neural stimulation increased phosphate content of the P-light chain in fast-twitch white muscle in a frequency-dependent manner, with lesser effects in fast-twitch red and slow-twitch muscles.