Effects of Low Cell pH and Elevated Inorganic Phosphate on the pCa-Force Relationship in Single Muscle Fibers at Near-Physiological Temperatures

Authors

Cassandra R. Nelson, Marquette UniversityFollow
Robert H. Fitts, Marquette UniversityFollow

Document Type

Article

Language

eng

Publication Date

4-2014

Publisher

American Physiological Society

Source Publication

American Journal of Physiology: Cell Physiology

Source ISSN

0002-9513

Abstract

Intense muscle contraction induces high rates of ATP hydrolysis with resulting increases in P_i, H⁺, and ADP, factors thought to induce fatigue by interfering with steps in the cross-bridge cycle. Force inhibition is less at physiological temperatures; thus the role of low pH in fatigue has been questioned. Effects of pH 6.2 and collective effects with 30 mM P_i on the pCa-force relationship were assessed in skinned fast and slow rat skeletal muscle fibers at 15 and 30°C. At 30°C, pH 6.2 + 30 mM P_i significantly depressed peak force in all fiber types, with the greatest effect in type IIx fibers. Across fiber types, Ca²⁺ sensitivity was depressed by low pH and low pH + high P_i, with the greater effect at 30°C. For type IIx fibers at 30°C, half-maximal activation (pCa₅₀) was 5.36 at pH 6.2 (no added P_i) and 4.98 at pH 6.2 + 30 mM P_i compared with 6.58 in the control condition (pH 7, no added Pi). At 30°C, n₂, reflective of thick filament cooperativity, was unchanged by low cell pH but was depressed from 5.02 to 2.46 in type IIx fibers with pH 6.2 + 30 mM P_i. With acidosis, activation thresholds of all fiber types required higher free Ca²⁺ at 15 and 30°C. With the exception of type IIx fibers, the Ca²⁺ required to reach activation threshold increased further with added P_i. In conclusion, it is clear that fatigue-inducing effects of low cell pH and elevated P_i at near-physiological temperatures are substantial.

Comments

Accepted version. American Journal of Physiology: Cell Physiology, Vol. 306, No. 7 (April 2014): C670-C678. DOI. © 2019 the American Physiological Society. Used with permission.

Recommended Citation

Nelson, Cassandra R. and Fitts, Robert H., "Effects of Low Cell pH and Elevated Inorganic Phosphate on the pCa-Force Relationship in Single Muscle Fibers at Near-Physiological Temperatures" (2014). Biological Sciences Faculty Research and Publications. 590.
https://epublications.marquette.edu/bio_fac/590