Response of Alpha-actinin Isoforms to Mechanical Ventilation-induced Diaphragmatic Atrophy

Abstract

Alpha-actinins are actin-binding proteins and important structural components of the Z-line. In mammalian skeletal muscle, the two isoforms are expressed, α-actinin-2 and α-actinin-3. α-actinin-2 is expressed in all skeletal muscles fibers, whereas α-actinin-3 expression is restricted to the fast fibers only, thus, α-actinin-3 is assumed to be associated with fast muscle fiber function. We previously examined α-actinin-3 level in the soleus muscle by using hindlimb unloading. This type of disuse induces the atrophy particularly in slow muscle fibers. In contrast, fast fibers are also atrophied by diaphragmatic inactivity, indicate that response of α-actinin-3 to atrophic stimuli with mechanical ventilation (MV) may differ from results of locomotor muscle disuse. PURPOSE: To examine the expression levels of α-actinin isoforms in rat diaphragm after MV. METHODS: Male Wistar rats were randomly divided into a control (n=5) or a 12h of MV (n=5) group. Mechanically ventilated animals were anesthetized, tracheostomized, and ventilated with 21% O2. Animals in the control group were acutely anesthetized but were not exposed to MV. After the treatment, diaphragms were removed, frozen with lipid nitrogen and stored at -80°C. Western blotting analysis was performed to Myosin heavy chain (MyHC) composition and expression of α-actinin isoforms. RESULTS: MV resulted in a decrease (14.0%, p < 0.01) in the cross-sectional area of diaphragm. MyHC composition did not differ between MV (I: 21.4, IIa: 19.3, IId/x: 49.2, IIb: 10.4%) and control (I: 22.2, IIa: 18.3, IId/x: 48.3, IIb: 11.2%) animals. Furthermore, there was no significant difference in expression levels of α-actinin isoforms between MV and control groups. CONCLUSION: The expression levels of α-actinin isoforms in rat diaphragm are not changed by the 12-h MV.