ARTICLE

¹ From the Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195.

Dr. Harris's present address is the Department of Biochemistry, University of Washington School of Medicine, Seattle, Washington 98195

The maximal calcium-activated isometric tension produced by a skinned frog single muscle fiber falls off as the ionic strength of the solution bathing this fiber is elevated declining to zero near 0.5 M as the ionic strength is varied using KCl. When other neutral salts are used, the tension always declines at high ionic strength, but there is some difference between the various neutral salts used. The anions and cations can be ordered in terms of their ability to inhibit the maximal calcium-activated tension. The order of increasing inhibition of tension (decreasing tension) at high ionic strength for anions is propionate^- SO₄^-- < Cl^- < Br^-. The order of increasing inhibition of calcium-activated tension for cations is K⁺ Na⁺ TMA⁺ < TEA⁺ < TPrA⁺ < TBuA⁺. The decline of maximal calcium-activated isometric tension with elevated salt concentration (ionic strength) can quantitatively explain the decline of isometric tetanic tension of a frog muscle fiber bathed in a hypertonic solution if one assumes that the internal ionic strength of a muscle fiber in normal Ringer's solution is 0.14–0.17 M. There is an increase in the base-line tension of a skinned muscle fiber bathed in a relaxing solution (no added calcium and 3 mM EGTA) of low ionic strength. This tension, which has no correlate in the intact fiber in hypotonic solutions, appears to be a noncalcium-activated tension and correlates more with a declining ionic strength than with small changes in [MgATP], [Mg], pH buffer, or [EGTA]. It is dependent upon the specific neutral salts used with cations being ordered in increasing inhibition of this noncalcium-activated tension (decreasing tension) as TPrA⁺ < TMA⁺ < K⁺ Na⁺. Measurements of potentials inside these skinned muscle fibers bathed in relaxing solutions produced occasional small positive values (<6 mV) which were not significantly different from zero.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Facebook    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				A. M. Gordon, E. Homsher, and M. Regnier Regulation of Contraction in Striated Muscle Physiol Rev, April 1, 2000; 80(2): 853 - 924. [Abstract] [Full Text] [PDF]

				B. M. MILLMAN The Filament Lattice of Striated Muscle Physiol Rev, April 1, 1998; 78(2): 359 - 391. [Abstract] [Full Text] [PDF]

				G.-R. Li, M. Zhang, L. S. Satin, and C. M. Baumgarten Biphasic effects of cell volume on excitation-contraction coupling in rabbit ventricular myocytes Am J Physiol Heart Circ Physiol, April 1, 2002; 282(4): H1270 - H1277. [Abstract] [Full Text] [PDF]

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents