Maximum velocity of shortening related to myosin isoform composition in frog skeletal muscle fibres.

Abstract

SUMMARY1. The velocity of unloaded shortening (VI), the myofibrillar ATPase activity and the immunoreactivity to two monoclonal antibodies (A1 and A2) that were raised against the myosin heavy chains were studied in single fibres of the anterior tibialis muscle of Rana temporaria. VO was recorded for the fibre as a whole using the slacktest method. Myofibrillar ATPase activity was determined by means of a quantitative histochemical technique.2. A highly significant, direct relationship was found to exist between V0 and the myofibrillar ATPase activity recorded in the same single fibres. Both VJ and the myofibrillar ATPase activity changed in proportion to the cross-sectional area of the fibres.3. Muscle fibres that had first been characterized with respect to V0 and myofibrillar ATPase activity were exposed to monoclonal antibodies Al and A2. Thin fibres, having relatively low V0 and low myofibrillar ATPase activity, reacted preferentially with A 1. Thick fibres, on the other hand, exhibiting relatively high V0 and high myofibrillar ATPase activity, were preferentially stained by A2. A third category of fibres reacted with both Al and A2. The results support the view that the variability in shortening velocity and myofibrillar ATPase activity that exists among twitch fibres in frog skeletal muscle is based on differences in myosin heavychain composition.4. Attempts were made to elucidate further the previous observation (Edman, Reggiani & te that the velocity of unloaded shortening (V0) differs along the length of individual muscle fibres. To this end discrete segments (0 5-0 7 mm in length) of intact fibres were delineated by opaque markers of hair that were placed on the fibre surface. The change in length between two adjacent markers (one segment) was recorded photo-electrically while the fibre was released to shorten against a very small load between 2-2 and 2-0 sm sarcomere lengths. In the majority of fibres (eight out of eleven preparations), V0 and myofibrillar ATPase activity exhibited similar patterns of variation along the fibre. Pooled data from thirty-three segments of twelve fibres showed a positive correlation between V0 and myofibrillar ATPase activity (P < 005).* On study leave from the Institute of Human Physiology, University of Pavia, Italy. K. A. P. EDMAN AND OTHERS5. The possibility was explored that the myosin isoform composition might vary along the length of an individual muscle fibre. For this purpose bundles of fibres were cross-sectioned at 0 5-1 mm intervals along their entire length and the reactivity to monoclonal antibody A2 was tested at each location. Clear differences in immunoreactivity tc A2 were demonstrable along the length of ten out of sixty-six fibres examined. These results provide evidence that the myosin heavy-chain composition may differ from one region to another within a single muscle fibre. Such a variation in myosin isoform composition may, at least partly, account for the segmental differences in contractile properties that are found to exist along the length of...

Single-fiber myosin heavy chain polymorphism: how many patterns and what proportions?

“…Collectively, segmental variations in MHC isoform expression (16,30) and the presence of polymorphic fibers that do not adhere to the sequential scheme (both under steady-state and transitional conditions) provide important pieces of evidence demonstrating that the genetic regulation of MHC isoform composition is sufficiently complex that it may not be simply described by the I7I/IIA7IIA7IIA/IIX7IIX7IIX/ IIB7IIB scheme. Does this mean that all fiber transitions do not adhere to this scheme?…”

Force‐velocity relations and myosin heavy chain isoform compositions of skinned fibres from rat skeletal muscle.

“…A relation between shortening velocity and ATPase activity and MHC isoform composition has been found in studies performed on rat ventricular myocardium (Mercandier, Lompre, Wisnewsky, Samuel, Bercovici, Swinghedauw & Schwartz, 1981), rabbit single skinned muscle fibres (Reiser, Moss, Giulian & Greaser, 1985), avian single skinned fibres and frog muscle fibres (Edman, Reggiani, Schiaffino & te Kronnie, 1988). Recent studies, however, have shown a large variability in shortening velocity among mammalian fibres containing fast MHC .…”

Additional in-series compliance reduces muscle force summation and alters the time course of force relaxation during fixed-end contractions

“…Contractile speed, including the maximum velocity of fibre shortening and maximum rates of force development and relaxation, is governed by the kinetics of actinmyosin interaction and sarcoplasmic reticulum Ca 2+ release and reuptake (Briggs et al, 1977;Edman et al, 1988;Metzger and Moss, 1990;Gordon et al, 2000). Fibre type-specific expressions of the motor protein myosin (Edman et al, 1988;Bottinelli et al, 1991), and fibre type-related differences in Ca 2+ dynamics (Baylor and Hollingworth, 2003;Barclay, 2012) and contractile apparatus Ca 2+ sensitivity (Stephenson and Williams, 1981) mean that the mechanical output of whole muscle is also a function of fibre type composition (Harridge et al, 1996). The performance of skeletal muscle in functional terms, as either a powerful motor or brake, is ultimately dependent on both high contractile force and speed being effectively transferred to the skeletal system.…”