Functional properties of skinned rabbit skeletal and cardiac muscle preparations containing a-cardiac myosin heavy chain

Abstract

Contractile properties of skinned muscle fibres from the masseter muscle and strips of heart atrium muscle from rabbits, both containing the alpha-cardiac myosin heavy chain isoform (alpha-cardiac MHC), were investigated and compared with those of other skeletal muscle fibre types. The stretch-induced delayed force increase (stretch activation) was investigated on maximally Ca(2+)-activated skinned preparations as an index of the kinetic properties of the myosin heads of various MHC isoforms. Skeletal muscle fibres containing exclusively alpha-cardiac MHC (type alpha) and muscle strips of heart atrium showed specific kinetics of stretch activation intermediate between those of types IIA and I fibres. In agreement with available data the unloaded shortening velocity V(u) of type alpha fibres was also intermediate between that of types IIA and I fibres. Compared with skeletal muscle type alpha fibres, muscle strips of heart atrium exhibited significantly (P<0.001) faster kinetics of both stretch activation and V(u). We conclude that type alpha fibres have characteristic kinetic properties that fill the gap between the fast type II and the slow type I fibres, and the following order of velocity can be established: IIB>IID(X)>IIA>alpha>I.

Kinetic properties of myosin heavy chain isoforms in mouse skeletal muscle: comparison with rat, rabbit, and human and correlation with amino acid sequence

“…The following combinations of MHC isoforms were found: MHCIIb and MHCIIx(d) (type IIBX), MHC IIa and MHCIIx(d) (type IIAX), and MHCIIa and MHCI (type C). Sarcomere lengths measured under resting conditions were similar in different fiber types (Table 1), which is in accordance with other mammalian species (3,7,19). The cross-sectional area (measured in relaxation solution containing 40 g/l dextran T-500) differed in different pure fiber types (see Table 1).…”

“…Although the same relationship between stretch activation kinetics and MHC isoforms was found for mouse, rat, rabbit, and human fibers (3,17,19,26), the t 3 values of corresponding fiber types within different animal species are not identical in these mammalian species. Figure 4 shows a double logarithmic plot of the velocity parameter 1/t 3 (mean Ϯ SD) of mouse, rat, rabbit, and human fiber types against the corresponding body mass.…”

“…For type II fibers, this is in accord with findings in other mammalian species. However, in contrast to mouse fibers, the t 3 values of rat, rabbit, and human type I fibers did not show a Gaussian distribution (2,3,17,26). A Gaussian distribution generally indicates that the data originate from one single identity.…”

“…Furthermore, V u was compared with the actin filament sliding propelled by the different myosin isoforms (28,39). The kinetics of stretch activation has never been investigated in mouse skeletal muscle fibers, although a strong correlation of this parameter with the MHC isoforms has been found in other species (3,12,16,17,19,24,26,33). This correlation most likely points to different kinetic properties of myosin heads of various MHC isoforms while generating force (1,31,34).…”

Expression of eight distinct MHC isoforms in bovine striated muscles:evidence for MHC-2B presence only in extraocular muscles

“…Fibres were dissected from rabbit masseter and their v 0 was intermediate between slow and fast 2A fibres. Similar conclusions were reached in a recent study (Andruchov et al, 2004) where tension transients after a small and fast elongation were analysed. Our results indicate that fibres containing MHC-␣ are similar to hybrid 1-2A fibres in their speed of shortening, tension development and, thus, in power output.…”