Abstract
Extensive variations exist in the heavy and light chain components of myosin in vertebrate striated muscles. In the present study, we have characterized a specific contractile property, velocity of shortening, and protein subunit composition of single fibers from adult rabbit soleus muscles. Maximum velocity of shortening (Vmax) was measured using the slack test method, and the myosin composition of these same fibers was determined using an ultrasensitive sodium dodecyl sulfate-polyacrylamide gel electrophoresis system. While most fibers were found to have velocities between 0.5 and 1.0 muscle length/s, several had velocities distributed between 1.33 and 2.99 muscle length/s. The fibers in the slower group had myosin subunits that were solely of the slow type; however, those in the faster group contained both fast and slow heavy chains and light chains. The velocity of shortening measured in fibers having both myosin types was highly correlated with the myosin heavy chain composition, with velocity increasing as the proportion of fast-type heavy chain increased. Variations in light chain composition, particularly fast and slow myosin light chain 1, appeared to occur independently of the variations in heavy chain composition, suggesting that some myosin molecules consist of mixtures of slow- and fast-type subunits.
Highlights
Our results indicate that 1)fastfibers was determined using an ultrasensitive sodium and slow-type myosins frequently occur within the same adult dodecyslulfate-polyacrylamide gel electrophoresis soleus fiber; 2) within a single fiber having mixed myosin system
The velocity of shortening measured ifnibershavingboth myosin typewsas sometimes different from the ratio of fastto slowheavy chains; and 3) shortening velocity in soleus fibers is highly correlated with the proportion of total heavy chain that is of the fast type
Highly correlated with the myosin heavy chain composition, withvelocity increasing as the proportionof fast-type heavychainincreased.Variationsinlight
Summary
Maximum velocity of myosin heavy chain and light chain compositions and the shortening (Vmax)was measured using the slack test maximum shortening velocities of single fibers from adult method,andthemyosincompositionofthesesame soleus muscles of the rabbit. While mostfibers were found to have velocities types, the ratio of total fast tototal slow light chain is between 0.5 and 1.0 muscle length/s, several had velocities distributedbetween 1.33 and 2.99 muscle lengthsls. The fibers in the slower group had myosin subunits that were solely of the slow type; those in thefaster group contained both fast and slow heavy chains and light chains.
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