Abstract
We found that organic solutes potently compress the myofilament lattice of skinned skeletal muscle. This compressing effect cannot be ascribed to the ordinary osmotic compression due to the filtration of the solutes by the lattice, because some solutes smaller than ATP in molecular weight could effectively compress the muscle. Another candidate for the compressing force comes from the entropic aggregating force of the macromolecules constituting the myofilament lattice. As Asakura-Oosawa theory and its derivatives describe, the aggregation of macromolecules in the presence of smaller particles depends on the exclusion of the particles from the very vicinity of the macromolecule surface. To estimate the effective exclusion volume for the organic solutes in the myofilament lattice, we examined the compressing effects of a series of organic molecules from mono- and poly-hydric alcohols. The results clearly indicated that the compressing efficiency of the alcohols depends primarily on the number of CH2 group that is not directly attached by the hydroxyl group. That is, the unitary component for the compressing effect is a single CH2 group. Since the molecular size of the CH2 group is very close to that of the water molecule (OH2; 0.31 nm3), any macromolecular aggregation force due to the exclusion of solutes would not work, unless each CH2 group forms a larger complex with surrounding water molecules or water molecules form a stable cluster larger than the bare CH2 group. The possibility of the CH2-OH2 complex formation and the stable water cluster formation will be discussed. [J Physiol Sci. 2006;56 Suppl:S78]
