Phosphate and Acidosis Act Synergistically to Depress Peak Power in Rat Muscle Fibers

Authors

Cassandra R. Nelson, Marquette UniversityFollow
Edward P. Debold, University of Massachusetts-Amherst
Robert H. Fitts, Marquette UniversityFollow

Document Type

Article

Language

eng

Format of Original

12 p.

Publication Date

11-2014

Publisher

American Physiological Society

Source Publication

American Journal of Physiology - Cell Physiology

Source ISSN

0002-9513

Original Item ID

doi: 10.1152/ajpcell.00206.2014

Abstract

Skeletal muscle fatigue is characterized by the buildup of H⁺ and inorganic phosphate (P_i), metabolites that are thought to cause fatigue by inhibiting muscle force, velocity, and power. While the individual effects of elevated H⁺ or P_i have been well characterized, the effects of simultaneously elevating the ions, as occurs during fatigue in vivo, are still poorly understood. To address this, we exposed slow and fast rat skinned muscle fibers to fatiguing levels of H⁺ (pH 6.2) and P_i (30 mM) and determined the effects on contractile properties. At 30°C, elevated P_i and low pH depressed maximal shortening velocity (V_max) by 15% (4.23 to 3.58 fl/s) in slow and 31% (6.24 vs. 4.55 fl/s) in fast fibers, values similar to depressions from low pH alone. Maximal isometric force dropped by 36% in slow (148 to 94 kN/m²) and 46% in fast fibers (148 to 80 kN/m²), declines substantially larger than what either ion exerted individually. The strong effect on force combined with the significant effect on velocity caused peak power to decline by over 60% in both fiber types. Force-stiffness ratios significantly decreased with pH 6.2 + 30 mM P_i in both fiber types, suggesting these ions reduced force by decreasing the force per bridge and/or increasing the number of low-force bridges. The data indicate the collective effects of elevating H⁺ and P_i on maximal isometric force and peak power are stronger than what either ion exerts individually and suggest the ions act synergistically to reduce muscle function during fatigue.

Comments

Accepted version. American Journal of Physiology - Cell Physiology, Vol. 307, No. 10 (November 2014): C939-C950. DOI. © 2014 American Physiology Society. Used with permission.

Recommended Citation

Nelson, Cassandra R.; Debold, Edward P.; and Fitts, Robert H., "Phosphate and Acidosis Act Synergistically to Depress Peak Power in Rat Muscle Fibers" (2014). Biomedical Sciences Faculty Research and Publications. 55.
https://epublications.marquette.edu/biomedsci_fac/55