Metabolic capacity and myosin expression in single muscle fibres of the garter snake.

Abstract

SUMMARY1. The transversus abdominis muscle of the garter snake contains fibres of three types: tonic (T), slower twitch (S) and faster twitch (F). Fibre types can be determined by anatomical criteria in living preparations. Individual fibres identified as T, S or F were excised from the muscle and subdivided for two types of biochemical examination. Enzymes of energy metabolism were assayed using quantitative microfluorometric methods. Myosin heavy chain composition was determined by gel electrophoresis. In separate experiments, twitch time-to-peaks of F and S fibres were measured to assess the range of contraction times present within the muscle's twitch fibre population.2. Metabolic subgroups of fibres were delineated by the relative activities of adenylokinase (AK), lactate dehydrogenase (LDH) and ,-hydroxyacyl-CoA-dehydrogenase (/JOAC). The metabolic subgroups corresponded to the anatomical fibre types. Type F fibres had high levels of enzymes associated with glycolytic (LDH) and high-energy phosphate (AK) metabolism. Type T fibres had high levels of the oxidative enzyme /JOAC. Type S fibres had both types of enzyme activity in intermediate and variable amounts.3. Three myosin heavy chain isoforms were present in the muscle. Type F and type T fibres each expressed a single isoform, denoted F and T respectively. Type S fibres expressed significant quantities of two isoforms: an isoform unique to this fibre type (denoted S) and the F isoform.4. Electrophoretic mobility and antibody reactivity of the F myosin heavy chain isoform resembled that of mammalian fast-twitch myosin. By the same criteria, the T isoform resembled mammalian slow-twitch myosin. The S isoform exhibited intermediate characteristics: its antibody reactivity was similar to mammalian fasttwitch myosin, but its electrophoretic mobility was that of mammalian slow-twitch myosin.5. Based on whole-muscle analysis, two myosin alkali light chains, denoted ALCI and ALC2, and one myosin regulatory light chain were present. Gel patterns suggested that ALCI and ALC2 exist as both homodimers and heterodimers. MS 8961 R. S. WILKINSON AND OTHERS6. The population of type S fibres within a given muscle exhibited a much wider range of twitch contraction times than did the population of type F fibres. Diversity of contractile properties among type S fibres may result, in part, from differential coexpression of two myosin heavy chain isoforms, together with highly variable ratios of enzymes from two major metabolic pathways.7. The clear biochemical distinction among fibre types indicates that each type possesses a unique and limited range of physiological properties. Based on this evidence, it is argued that intrinsic fibre types contribute towards generation of functional diversity within the muscle's fibre population.

Electrophoretic separation of reptilian skeletal and cardiac muscle myosin heavy chain isoforms: Dependence on gel format

“…There are few reports of electrophoretic separation of reptilian MHC isoforms. One report indicates the presence of three MHC isoforms in the transversus abdominis muscle of the garter snake ( Thamnophis sirtalis ), using a separating gel format that included 6% acrylamide and 40% glycerol. It appears that a high glycerol concentration in separating gels is important for separating MHC isoforms among reptilian species, consistent with the original report of the effects of high glycerol concentration in SDS gels on the separation of mammalian MHC isoforms .…”

Retrograde flow rate is increased in growth cones from myosin IIB knockout mice

“…The interaction of these two myosins in growth cones is analogous to the differences observed in speed of contraction of skeletal muscle fibers. Fast and slow skeletal muscle fibers have different myosin isoforms that have different contraction speeds and ATPase activities (Wilkison et al, 1991). Some muscle fibers have mixtures of myosin isoforms and their contractile properties reflect this combination.…”