Mitochondrial efficiency and exercise economy following heat stress: a potential role of uncoupling protein 3.
Heat stress has been reported to reduce uncoupling proteins (UCP) expression, which in turn should improve mitochondrial efficiency. Such an improvement in efficiency may translate to the systemic level as greater exercise economy. However, neither the heat-induced improvement in mitochondrial efficiency (due to decrease in UCP), nor its potential to improve economy has been studied. Determine: (i) if heat stress in vitro lowers UCP3 thereby improving mitochondrial efficiency in C2C12 myocytes; (ii) whether heat acclimation (HA) in vivo improves exercise economy in trained individuals; and (iii) the potential improved economy during exercise at altitude. In vitro, myocytes were heat stressed for 24 h (40°C), followed by measurements of UCP3, mitochondrial uncoupling, and efficiency. In vivo, eight trained males completed: (i) pre-HA testing; (ii) 10 days of HA (40°C, 20% RH); and (iii) post-HA testing. Pre- and posttesting consisted of maximal exercise test and submaximal exercise at two intensities to assess exercise economy at 1600 m (Albuquerque, NM) and 4350 m. Heat-stressed myocytes displayed significantly reduced UCP3 mRNA expression and, mitochondrial uncoupling (77.1 ± 1.2%, P < 0.0001) and improved mitochondrial efficiency (62.9 ± 4.1%, P < 0.0001) compared to control. In humans, at both 1600 m and 4350 m, following HA, submaximal exercise economy did not change at low and moderate exercise intensities. Our findings indicate that while heat-induced reduction in UCP3 improves mitochondrial efficiency in vitro, this is not translated to in vivo improvement of exercise economy at 1600 m or 4350 m.
Department of Health, Exercise and Sports Sciences, University of New Mexico, Albuquerque, New Mexico roy.m.salgado.ctr@mail.mil.
Roy M
RM
Salgado
Department of Health, Exercise and Sports Sciences, University of New Mexico, Albuquerque, New Mexico.|School of Kinesiology and Nutritional Science, California State University Los Angeles, Los Angeles, California.
Ailish C
AC
Sheard
Department of Exercise Science, High Point University, High Point, North Carolina.
Roger A
RA
Vaughan
Deparment of Kinesiology and Health Science, California State University Sacramento, Sacramento, California.
Daryl L
DL
Parker
Department of Health, Exercise and Sports Sciences, University of New Mexico, Albuquerque, New Mexico.
Suzanne M
SM
Schneider
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts.
Robert W
RW
Kenefick
Department of Health, Exercise and Sports Sciences, University of New Mexico, Albuquerque, New Mexico.
James J
JJ
McCormick
School of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin.
Nicholas P
NP
Gannon
Department of Health, Exercise and Sports Sciences, University of New Mexico, Albuquerque, New Mexico.|Department of Exercise and Sport Management, Kennesaw State University, Kennesaw, Georgia.
Trisha A
TA
Van Dusseldorp
Department of Health, Exercise and Sports Sciences, University of New Mexico, Albuquerque, New Mexico.
Len R
LR
Kravitz
Department of Health, Exercise and Sports Sciences, University of New Mexico, Albuquerque, New Mexico.
Christine M
CM
Mermier
D000064:Acclimatization; D000328:Adult; D000531:Altitude; D000818:Animals; D002460:Cell Line; D015444:Exercise; D018869:Heat-Shock Response; D006801:Humans; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D032342:Muscle Cells / Q000378:metabolism*; D010101:Oxygen Consumption; D000071247:Uncoupling Protein 3 / Q000378:metabolism*
C000604393:Ucp3 protein, mouse; D000071247:Uncoupling Protein 3
Altitude; cross‐tolerance; exercise capacity; heat acclimation; mitochondria