Abstract
Macromolecular solutes such as Dextran T500 (Mw 500,000), are known to compress the myofilament lattice of skinned skeletal muscle. Since large molecules would be physically excluded from the lattice, increase in the accessible water for the macromolecules is considered to favor the lattice shrinkage. We found that small molecules of polyethylene glycols (PEGs; Mw200 and 900) also compress the skinned fiber. To elucidate the mechanism, we pursued the effects of relevant small molecules on the fiber volume. The optical cross section of mechanically skinned fibers of frog sartorius muscle was observed. PEGs, ethylene glycol, butanols (butanol, butanediol, butanetriol), pentanols (pentanol, pentanediol) efficiently compressed the fibers, while glycerol, threitol, ribitol and mammitol did not. The number of hydrophobic groups and their distribution on the molecule would be the important factors. The molecules with compressing efficiency exerted diverse effects on fiber function. PEGs decreased Ca-sensitivity for activation, while butanol and pentanol increased it. All the tested molecules suppressed the maximal force with varied efficiency. No correlation was found between the efficiency for fiber compression, Ca-sensitization and maximum force suppression, indicating that the molecules selectively affect multiple sites on the myofilament. This suggested that the tested molecules could, at least partly, penetrate into the myofilament lattice. We infer that the network of hydration water in the myofilament lattice filters the hydrophobic molecules forming a heterogeneous field around the myofilaments. [Jpn J Physiol 55 Suppl:S122 (2005)]
