Cross-bridge kinetics of fast and slow fibres of cat jaw and limb muscles: correlations with myosin subunit composition

Abstract

Mechanical properties of the jaw-closing muscles of the cat are poorly understood. These muscles are known to differ in myosin and fibre type compositions from limb muscles. This work aims to correlate mechanical properties of single fibres in cat jaw and limb muscles with their myosin subunit compositions. The stiffness minimum frequency, f(min), which reflects isometric cross-bridge kinetics, was measured in Ca(2+)-activated glycerinated fast and slow fibres from cat jaw and limb muscles for temperatures ranging between 15 and 30 degrees C by mechanical perturbation analysis. At 15 degrees C, f(min) was 0.5 Hz for limb-slow fibres, 4-6 Hz for jaw-slow fibres, and 10-13 Hz for limb-fast and jaw-fast fibres. The activation energy for f(min) obtained from the slope of the Arrhenius plot for limb-slow fibres was 30-40% higher than values for the other three types of fibres. SDS-PAGE and western blotting using highly specific antibodies verified that limb-fast fibres contained IIA or IIX myosin heavy chain (MyHC). Jaw-fast fibres expressed masticatory MyHC while both jaw-fast and jaw-slow fibres expressed masticatory myosin light chains (MLCs). The nucleotide sequences of the 3' ends of the slow MyHC cDNAs isolated from cat masseter and soleus cDNA libraries showed identical coding and 3'-untranslated regions, suggesting that jaw-slow and limb-slow fibres express the same slow MyHC gene. We conclude that the isometric cross-bridge cycling kinetics of jaw-fast and limb-fast fibres detected by f(min) are indistinguishable in spite of differences in MyHC and light chain compositions. However, jaw-slow fibres, in which the same slow MyHCs are found in combination with MLCs of the jaw type, show enhanced cross-bridge cycling kinetics and reduced activation energy for cross-bridge detachment.

Masticatory (`superfast') myosin heavy chain and embryonic/atrial myosin light chain 1 in rodent jaw-closing muscles

“…These authors reported that masticatory MLC1 and 2 are associated with MHC-M in some fibers of cat masseter, consistent with Rowlerson et al (Rowlerson et al, 1981), and with slow-type MHC-I in other fibers of the same muscle, consistent with Sciote et al (Sciote et al, 1995). Furthermore, Hoh et al (Hoh et al, 2007) reported that the slow fibers in cat masseter have significantly faster contractile kinetics, compared with slow fibers in limb muscle, which express the same MHC isoform but not masticatory MLC1 or 2. This suggests that MLC1E/A and masticatory MLC1 have similar roles in modulating (increasing) contractile kinetics.…”

“…However, what needs to be considered is the gain (or loss) of function associated with the substitution of MLC1E/A for other MLC isoforms that would otherwise be associated with MHC-M. The results from Hoh et al (Hoh et al, 2007) are particularly interesting in this regard. These authors reported that masticatory MLC1 and 2 are associated with MHC-M in some fibers of cat masseter, consistent with Rowlerson et al (Rowlerson et al, 1981), and with slow-type MHC-I in other fibers of the same muscle, consistent with Sciote et al (Sciote et al, 1995).…”

Expression of Masticatory-specific Isoforms of Myosin Heavy-chain, Myosin-binding Protein-C and Tropomyosin in Muscle Fibers and Satellite Cell Cultures of Cat Masticatory Muscle

“…Our immunohistochemical results suggest that the jaw-slow fibers, which express the same slow MyHC as limb slow fibers (Hoh et al 2007b), express isoforms of Tm and MBP-C different from those in masticatory fibers. SDS-PAGE of myofibrillar proteins of the cat masseter included a band identical in mobility to limb b-Tm ( Figure 4D) and another band with a slightly higher mobility than m-MBP-C ( Figure 2E).…”

“…The functional characteristics of masticatory fibers include high Ca sensitivity (Kato et al 1985), high tension cost (Saeki et al 1987), high force-per-unit crosssectional area (Saeki et al 1987;Toniolo et al 2008), moderate cross-bridge cycling rate as indicated by dynamic stiffness analysis (Hoh et al 2007b), and moderate speed of shortening (Toniolo et al 2008). The high-tension cost is probably related to the high ATPase activity of the masticatory myosin (Rowlerson et al 1981), whose MyHCs and light chains are structurally distinct from those of limb muscle (Rowlerson et al 1981;Qin et al 1994Qin et al ,2002.…”

Chronic Low-Frequency Stimulation Transforms Cat Masticatory Muscle Fibers into Jaw-Slow Fibers

“…MAb 1A10 binds fetal MyHCs and jaw-slow, but not limb-slow, myosin. This capacity of MAb 1A10 to distinguish jaw-slow from limb-slow myosin is likely due to the association of masticatory myosin light chains with slow MyHCs in jaw-slow fibers (Hoh et al 2007). MAb CH1 reacts with all jaw and limb muscle tropomyosin isoforms (Hoh et al 1989).…”