Myosin conformation and enzymatic activity: effect of chloroform, diethyl ether and halothane on optical rotatory dispersion and APTase

Eccentric contraction-induced strength loss in dystrophin-deficient muscle: Preparations, protocols, and mechanisms

The absence of dystrophin hypersensitizes skeletal muscle of lower and higher vertebrates to eccentric contraction (ECC)-induced strength loss. Loss of strength can be accompanied by transient and reversible alterations to sarcolemmal excitability and disruption, triad dysfunction, and aberrations in calcium kinetics and reactive oxygen species production. The degree of ECC-induced strength loss, however, appears dependent on several extrinsic and intrinsic factors such as vertebrate model, skeletal muscle preparation (in vivo, in situ, or ex vivo), skeletal muscle hierarchy (single fiber versus whole muscle and permeabilized versus intact), strength production, fiber branching, age, and genetic background, among others. Consistent findings across research groups show that dystrophin-deficient fast(er)-twitch muscle is hypersensitive to ECCs relative to wildtype muscle, but because preparations are highly variable and sensitivity to ECCs are used repeatedly to determine efficacy of many preclinical treatments, it is critical to evaluate the impact of skeletal muscle preparations on sensitivity to ECC-induced strength loss in dystrophin-deficient skeletal muscle. Here, we review and discuss variations in skeletal muscle preparations to evaluate the factors responsible for variations and discrepancies between research groups. We further highlight that dystrophin-deficiency, or loss of the dystrophin-glycoprotein complex in skeletal muscle, is not a prerequisite for accelerated strength loss-induced by ECCs.

Effects of halothane on Ca2+-activated tension development in mechanically disrupted rabbit myocardial fibers

The effect of halothane on maximal and submaximal Ca2+-activated tension in mechanically disrupted right ventricular papillary muscle from rabbits was studied. Steady-state isometric tension generation was measured in the muscle bundle. The relaxing solution contained (in mM) [Mg2+] = 1, [K+] = 70, [MgATP2-] = 2, [creatine phosphate2-] = 15, [EGTA total] = 7 and imidazole proprionate. The contracting solution contained in addition Ca2+ in various concentrations. In all solutions ionic strength was maintained at 0.15 and pH at 7.00 +/- 0.02 at 20 degrees C. Each fiber bundle was immersed in control solutions equilibrated with 100% N2 and test solutions equilibrated with various concentrations of halothane-N2 mixture. Increasing doses of halothane (1--4%) significantly shifted the relationship between Ca2+ and tension towards higher [Ca2+] and depressed the maximum Ca2+-activated tension. The maximum tension generated at pCa = 3.8 was depressed 5% per 1% increase in halothane concentration. The percentage of maximum tension at submaximum Ca2+ concentrations (pCa = 5.6--5.0) was not significantly decreased until halothane concentration was greater than 2%. It is concluded that halothane slightly but significantly depressed the interactions of contractile proteins and to a lesser degree Ca2+-activation of the regulatory proteins. The halothane-induced depression was completely reversible.

Structural and enzymatic properties of cardiac myosin in ischaemic and non-ischaemic regions of the rat myocardium

In rats with ligation of the left coronary artery changes in ATPase activity and structure of cardiac myosin in both ischaemic and non-ischaemic zones of the myocardium were followed. In control animals, ATPase activity and the structure of the myosin molecule in right and left ventricles did not differ. Non-specific factors, such as anaesthesia and thoracotomy, can result in a decrease or an increase in ATPase activity respectively. One hour after ligation of the left coronary artery ATPase activity increased in the right, non-ischaemic myocardium and there was a significant right-to-left difference. Four hours after ligation, ATPase activity in both ventricles significantly decreased and the right-left difference disappeared. Within 48 h, normal values were found only in the non-ischaemic right ventricle. Ligation of the left coronary artery results after 48 h in the formation of structural alterations in cardiac myosin, primarily in the left, ischaemic myocardium. These changes are characterised by the formation of myosin aggregates, which have a significantly lower ATPase activity in comparison with monomeric myosin.

The effects of halothane on cultured mouse neuroblastoma cells. I. Inhibition of morphological differentiation

Mouse neuroblastoma cells (clone NB2a) were cultured in the presence of 0.3-2.1% halothane in the gas phase for up to 72 h. Halothane inhibited neurite extension dose dependently and virtually abolished microspike formation even at the lowest concentration tested. These effects were completely reversible. Electron microscopy demonstrated that microfilaments measuring 40-80 A in diameter are the only fibrous organelles visible within microspikes. When the cells were exposed to halothane, no microfilamentous complexes could be identified in any cells and the subcortical regions of neurites often appeared devoid of individual microfilaments. Microtubules were still present in neurites after exposure to halothane concentrations at which microfilaments disappeared. However, at concentrations above 1.0%, microtubules gradually appeared to decrease in number. Short-term experiments showed that existing neurites and microspikes rapidly retracted when suddenly exposed to culture medium equilibrated with 1.0% halothane and quickly reformed when the halothane was removed. The inhibition of neuroblastoma cell differentiation by halothane appears to be mediated by disruption of 40-80 A diameter microfilaments.