A quantitative study of bioenergetics in skeletal muscle lacking carbonic anhydrase III using 31P magnetic resonance spectroscopy

doi:10.1073/pnas.0609870104

A quantitative study of bioenergetics in skeletal muscle lacking carbonic anhydrase III using ³¹P magnetic resonance spectroscopy

*Department of Physical Therapy, University of Florida, Gainesville, FL 32610-0154; and
^†Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6085

Contributed by R. E. Forster, November 8, 2006 (received for review October 16, 2006)

Abstract

Oxidative slow skeletal muscle contains carbonic anhydrase III in high concentration, but its primary function remains unknown. To determine whether its lack handicaps energy metabolism and/or acid elimination, we measured the intracellular pH and energy phosphates by ³¹P magnetic resonance spectroscopy in hind limb muscles of wild-type and CA III knockout mice during and after ischemia and intense exercise (electrical stimulation). Thirty minutes of ischemia caused phosphocreatine (PCr) to fall and P_i to rise while pH and ATP remained constant in both strains of mice. PCr and P_i kinetics during ischemia and recovery were not significantly different between the two genotypes. From this we conclude that under neutral pH conditions resting muscle anaerobic metabolism, the rate of the creatine kinase reaction, intracellular buffering of protons, and phosphorylation of creatine by mitochondrial oxygen metabolism are not influenced by the lack of CA III. Two minutes of intense stimulation of the mouse gastrocnemius caused PCr, ATP, and pH to fall and ADP and P_i to rise, and these changes, with the exception of ATP, were all significantly larger in the CA III knockouts. The rate of return of pH and ADP to control values was the same in wild-type and mutant mice, but in the mutants PCr and P_i recovery were delayed in the first minute after stimulation. Because the tension decrease during fatigue is known to be the same in the two genotypes, we conclude that a lack of CA III impairs mitochondrial ATP synthesis.

mitochondrial ATP synthesis

Footnotes

^‡To whom correspondence should be addressed. E-mail: forster{at}mail.med.upenn.edu
Author contributions: M.L., G.A.W., R.E.F., and K.V. designed research; M.L. and N.C.P. performed research; M.L. and R.E.F. analyzed data; and M.L., G.A.W., R.E.F., and K.V. wrote the paper.
Some of these results were presented at the meeting of the International Society of Magnetic Resonance in Medicine in Miami Beach, FL, May 7–13, 2005.
The authors declare no conflict of interest.
Abbreviations:

Cr,

creatine;

MRS,

magnetic resonance spectroscopy;

PCr,

phosphocreatine;

pHi,

intracellular pH.