Faculty Collaboration Database

Effects of low cell pH and elevated inorganic phosphate on the pCa-force relationship in single muscle fibers at near-physiological temperatures. Am J Physiol Cell Physiol 2014 Apr 01;306(7):C670-8

Date

01/24/2014

Pubmed ID

24452378

DOI

10.1152/ajpcell.00347.2013

Scopus ID

2-s2.0-84900546685 (requires institutional sign-in at Scopus site)   53 Citations

Abstract

Intense muscle contraction induces high rates of ATP hydrolysis with resulting increases in Pi, 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 Pi 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 Pi significantly depressed peak force in all fiber types, with the greatest effect in type IIx fibers. Across fiber types, Ca(2+) sensitivity was depressed by low pH and low pH + high Pi, 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 Pi) and 4.98 at pH 6.2 + 30 mM Pi 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 Pi. With acidosis, activation thresholds of all fiber types required higher free Ca(2+) at 15 and 30°C. With the exception of type IIx fibers, the Ca(2+) required to reach activation threshold increased further with added Pi. In conclusion, it is clear that fatigue-inducing effects of low cell pH and elevated Pi at near-physiological temperatures are substantial.

Author List

Nelson CR, Fitts RH

Author

Robert Fitts PhD Professor in the Biological Sciences department at Marquette University

MESH terms used to index this publication - Major topics in bold

Acidosis
Animals
Body Temperature
Calcium Signaling
Female
Hydrogen-Ion Concentration
Male
Muscle Contraction
Muscle Fatigue
Muscle Fibers, Fast-Twitch
Muscle Fibers, Slow-Twitch
Muscle Strength
Phosphates
Rats
Rats, Sprague-Dawley