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LETTER TO THE EDITOR

Mitochondrial respiration in creatine-loaded muscle: is there ³¹P-MRS evidence of direct effects of phosphocreatine and creatine in vivo?

Recent human isolated muscle fiber studies suggest that phosphocreatine (PCr) and creatine (Cr) concentrations play a role in the regulation of mitochondrial respiration rate. To determine whether similar regulatory mechanisms are present in vivo, this study examined the relationship between skeletal muscle mitochondrial respiration rate and end-exercise PCr, Cr, PCr-to-Cr ratio (PCr/Cr), ADP, and pH by using ³¹P-magnetic resonance spectroscopy in 16 men and women (36.9 ± 4.6 yr). The initial PCr resynthesis rate and time constant (T_c) were used as indicators of mitochondrial respiration after brief (10–12 s) and exhaustive (1–4 min) dynamic knee extension exercise performed in placebo and creatine-supplemented conditions. The results show that the initial PCr resynthesis rate has a strong relationship with end-exercise PCr, Cr, and PCr/Cr (r > 0.80, P < 0.001), a moderate relationship with end-exercise ADP (r = 0.77, P < 0.001), and no relationship with end-exercise pH (r = –0.14, P = 0.34). The PCr T_c was not as strongly related to PCr, Cr, PCr/Cr, and ADP (r < 0.77, P < 0.001–0.18) and was significantly influenced by end-exercise pH (r = –0.43, P < 0.01). These findings suggest that end-exercise PCr and Cr should be taken into consideration when PCr recovery kinetics is used as an indicator of mitochondrial respiration and that the initial PCr resynthesis rate is a more reliable indicator of mitochondrial respiration compared with the PCr T_c.

REPLY

Health Sciences Programs
College of Nursing and Health Professions
Drexel University
Philadelphia, Pennsylvania
e-mail: sas86{at}drexel.edu

Scott J. Montain

US Army Research Institute of Environmental Medicine
Natick, Massachusetts
e-mail: scott.montain{at}us.army.mil

This article has been cited by other articles:

				G. Kemp Physiological implications of linear kinetics of mitochondrial respiration in vitro Am J Physiol Cell Physiol, September 1, 2008; 295(3): C844 - C846. [Full Text] [PDF]

				G. Kemp Altered creatine dependence of muscle mitochondrial respiration in vitro: what are the likely effects in vivo? J Appl Physiol, December 1, 2006; 101(6): 1814 - 1815. [Full Text] [PDF]