Abstract
Macromolecules, such as Dextran T500 (Mw 500k), have been considered to compress skinned fibers of skeletal muscle osmotically because they are too large to penetrate into myofilament lattice. However, we found that polyethylene glycols (PEG) of small molecular weight (Mw 3350 and 200) efficiently compress skinned fibers. From the size of the molecule, they are small enough to penetrate into the myofilament lattice. Since PEG was reported to affect interaction between proteins, we pursued the effects of relevant polyols on the volume of skinned fibers at rest. Fiber volume was measured as optical cross-sectional area of isolated skinned fibers from bullfrog sartorius muscle. Any polyols in the ethylene glycol (EG) series (EG, diEG, triEG, tetraEG, PEG200, PEG900, PEG3350, and cyclodextrins) compressed the fibers. Most efficient was PEG3350 (Mw 3350), which compressed the fiber volume to 25% of the original at 30% (w/w). Interestingly, even on mole fraction basis, EG (H-[CHOH]2-H) was as efficient as threitol (H-[CHOH]4-H), but more efficient than glycerol (H-[CHOH]3-H). Cyclodextrins (Mw 972-1297), which has characteristic molecular structure, were roughly as efficient as PEG200. PEG suppressed isometric force development of the fiber, while cyclodextrins significantly increased the isometric force as well as the rate of force rise on activation with Ca2+. These results indicated that the effects of polyols on skinned fibers were not a simple osmotic effect but reflect subtle structure of the molecules. The effect of macromolecules on muscle should be carefully reconsidered in this light. [Jpn J Physiol 54 Suppl:S119 (2004)]
