Energy state and myosin heavy chain isoforms in single fibres of normal and transforming rabbit muscles

Abstract

Energy-rich phosphates, [ATP]/[ADPfree] ratios, and the myosin heavy chain (MHC) complement were determined in single fibres from normal rabbit muscles, and in fibres isolated from tibialis anterior muscle undergoing fast-to-slow conversion by chronic low-frequency stimulation (CLFS). In normal muscles, energy-rich phosphate contents and [ATP]/[ADPfree] ratios could thus be assigned to different MHC-based fibre types. Phosphocreatine (PCr) contents and [ATP]/[ADPfree] ratios differed markedly between fast- and slow-twitch fibres, as well as within the fast fibre subtypes. Both magnitudes were approximately twofold higher in the fastest (type IIB) fibres as compared to the slowest (type I) fibres. According to PCr contents and [ATP]/[ADPfree] ratios pure and hybrid fibres were aligned in an order similar to that determined by their contractile properties and myofibrillar ATPase activities. CLFS for up to 30 days induced pronounced decreases in PCr and [ATP]/[ADPfree] which attained levels twofold lower than in normal slow-twitch fibres. In both normal and stimulated muscles, PCr and [ATP]/[ADPfree] ratios were correlated, indicating their equilibrium in the different fibre types. The relationship detected between MHC isoform expression and the [ATP]/[ADPfree] ratio suggests that the drastic and persistent depression of the cellular energy state may act as an important signal initiating fast-to-slow transformation processes in muscle fibres.

Functional and biochemical properties of chronically stimulated human skeletal muscle

“…Furthermore, as demonstrated Table 2 Results of chronic low-frequency stimulation (CLFS) inthe sham and CLFS groups. (ATWC Work capacity at the anaerobic threshold, ATV _O 2 oxygen uptake at the anaerobic threshold, BPD diastolic blood pressure, BPS systolic blood pressure, HR heart rate, Peak-RER peak respiratory exchange ratio) in rabbit muscle by single fiber electrophoresis, CLFS results in pronounced increases in fibers displaying the co-existence of MHCIIa and MHCI during the type IIA to type I fiber transformation (Staron et al 1987;Conjard et al 1998;Peuker et al 1998). …”

Differential Expression of Equine Myosin Heavy-chain mRNA and Protein Isoforms in a Limb Muscle

“…Also in human muscle, mismatch between MyHC mRNA and protein or MyHC-ATPase reactivity could not be attributed to variations in myosin composition along the length of the fiber because the staining of fibers did not change after extended analysis of serial sections (Andersen and Schiaffino 1997). Single-fiber analysis has shown that the MyHC expression can vary along the length of the fiber, but over distances in the millimeter range, much larger than the distances between the serial sections presented here (Peuker and Pette 1997;Conjard et al 1998). …”

Myosin Heavy Chain Isoforms in Equine Gluteus Medius Muscle: Comparison of mRNA and Protein Expression Profiles

“…Upon this induced transformation, regardless of the type of protocol applied, more mismatching between mRNA and protein expression is observed (Andersen and Schiaffino 1997;Conjard et al 1998;Andersen et al 1999a;Stevens et al 1999). Clearly, analyzing muscle fibers (pure and hybrid) at the mRNA and protein level is important for understanding the steady-state situation and the transformation process.…”

“…Another study (Conjard et al 1998) analyzed single fibers from rabbit rectus femoris, extensor digitorum longus, tibialis anterior, and soleus muscle. mRNA MyHC isoform patterns were consistent with MHC protein profiles, including hybrid fibers, in the majority of fibers from normal, untransforming muscle (Conjard et al 1998). In rat, single fibers from the soleus muscle were analyzed; in Table 1D) stained with the indicated mRNA probes (left panels) or with the indicated antibodies (right panels).…”