Phosphorylation of rabbit skeletal muscle myosin in situ

Abstract

Myosin light chain (P light chain) is phosphorylated by Ca2+ X calmodulin-dependent myosin light chain kinase. Based on studies with rat skeletal muscles, it has been shown that P light chain phosphorylation correlated to the extent of potentiation of isometric twitch tension. It is not clear whether this correlation exists in rabbit skeletal muscle, which has been the primary source of contractile proteins for biochemical studies. Therefore, phosphorylation of myosin P light chain in rabbit slow-twitch soleus and fast-twitch plantaris muscles in situ was examined. Electrical stimulation (5 Hz, 20 seconds) of plantaris muscle produced an increase in the phosphate content of P light chain from 0.17 to 0.45 mol phosphate/mol P light chain. This increase in phosphate content was accompanied by a 58% increase in maximal isometric twitch tension. Tetanic stimulation (100 Hz, 15 seconds) of rabbit soleus muscle resulted in only a small increase in P light chain phosphate content from 0.02 to 0.10 mol phosphate/mol P light chain, and posttetanic twitch tension did not increase significantly. The correlation between potentiated isometric twitch tension and P light chain phosphorylation in rabbit fast-twitch muscle is similar to that observed in rat skeletal muscle. These results were consistent with the hypothesis that phosphorylation of rabbit skeletal muscle myosin, which results in an increase in actin-activated ATPase activity, may be related to isometric twitch potentiation.

Alteration of cross-bridge kinetics by myosin light chain phosphorylation in rabbit skeletal muscle: implications for regulation of actin-myosin interaction.

“…(26), repetitive stimuli lead to activation of myosin light chain kinase and myosin light chain phosphorylation (10)(11)(12)(13). This phosphorylation will increase the rate of tension production as well as the tension-time integral about 2-fold (10)(11)(12)(13)27).…”

“…However, subsequent work in skinned and intact skeletal muscle fibers did not support a causal relationship (7)(8)(9). The only known physiological correlation to myosin light chain phosphorylation is an increase in the rate of force development and potentiation of isometric twitch tension in fast-twitch skeletal muscle fibers (10)(11)(12)(13). Myosin light chain phosphorylation causes an increase in force production at low levels of calcium activation (14,15) and also causes an increased rate of force development (16) over a wide range of activation levels in permeable skeletal muscle fibers.…”

Regulatory domains of myosins: influence of heavy chain on Ca2+-binding

“…Phosphorylation of smooth and non-muscle myosin RLCs also facilitates filament assembly in the presence of ATP (Onishi & Wakabayashi, 1982;Trybus et al, 1982;Cross et al, 1986;Kendrick-Jones et al, 1987). Phosphorylation of rabbit RLC may play a role in the post-tetanic potentiation of tension generation (Moore et aL, 1985). It has also been proposed that molluscan catch myosins are regulated both by direct Ca2+-binding and RLC phosphorylation (Takahashi et al, 1988).…”

Enhanced Skeletal Muscle Contraction with Myosin Light Chain Phosphorylation by a Calmodulin-sensing Kinase

“…When detectable, stimulation-induced RLC phosphorylation in slow-twitch muscle required higher frequencies and longer stimulation times than did fast-twitch muscle, conditions that typically lead to fatigue (11-13). Likewise, twitch force potentiation was more robust in fast-versus slow-twitch muscle (13,14). Reduced RLC phosphorylation may be due to lower skMLCK and greater myosin phosphatase activities in slow-twitch muscle (13).…”