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Differential Osmotic Behavior of Water Components in Living Skeletal Muscle Resolved by ¹H-NMR

Department of Physiology, Jikei University School of Medicine, Minato-ku, Tokyo 105-8461, Japan

Correspondence: Address reprint requests to Masako Kimura, Dept. of Physiology, Jikei University School of Medicine 3-25-8, Nishishinbashi, Minato-ku, Tokyo 105-8461, Japan. Tel.: 81-3-3431-3827; Fax: 81-3-3431-3827; E-mail: masako{at}jikei.ac.jp.

Using frog sartorius muscle, we observed transverse relaxation processes of ¹H-NMR signals from myowater. The process could be well described by four characteristic exponentials: the extremely slow exponential of relaxation time constant T₂ > 0.4 s, the slow one of T₂ 0.15 s, the intermediate one of 0.03 s < T₂ < 0.06 s, and the rapid one of T₂ < 0.03 s. Addition of isotonic extracellular solution affected only the extremely slow exponential, linearly increasing its amplitude and gradually increasing its T₂ toward that of the bulk solution (1.7 s). Therefore, this exponential should represent extracellular surplus solution independently of the other exponentials. At two thirds to three times the isotonicity, the amplitude of the intermediate exponential showed normal osmotic behavior in parallel with the volume change of the myofilament lattice measured with x-ray diffraction. In the same tonicity range, the amplitude of the rapid exponential showed converse osmotic behavior. Lower tonicities increased the amplitude of only the slow exponential. Studied tonicities did not affect the T₂ values. The distinct osmotic behavior indicated that each characteristic exponential could be viewed as a distinct water group. In addition, the converse osmotic behavior suggested that the rapid exponential would not be a static water layer on the macromolecule surface.

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