Resting oxygen consumption and in vivo ADP are increased in myopathy due to complex I deficiency.
BACKGROUND
Patients with isolated complex I deficiency (CID) in skeletal muscle mitochondria often present with exercise intolerance as their major clinical symptom.


OBJECTIVE
To study the in vivo bioenergetics in patients with complex I deficiency in skeletal muscle mitochondria.


METHODS
In vivo bioenergetics were studied in three of these patients by measuring oxygen uptake at rest and during maximal exercise, together with forearm ADP concentrations ([ADP]) at rest. Whole-body oxygen consumption at rest (VO(2)) was measured with respiratory calorimetry. Maximal oxygen uptake (VO(2)max) was measured during maximal exercise on a cycle ergometer. Resting [ADP] was estimated from in vivo (31)P MRS measurements of inorganic phosphate, phosphocreatine, and ATP content of forearm muscle.


RESULTS
Resting VO(2) was significantly increased in all three patients: 128 +/- 14% (SD) of values in healthy control subjects. VO(2)max in patients was on average 2.8 times their VO(2) at rest and was only 28% of VO(2)max in control subjects. Resting [ADP] in forearm muscle was significantly increased compared with healthy control subjects (patients 26 +/- 2 microM, healthy controls 9 +/- 2 microM).


CONCLUSIONS
In patients with CID, the increased whole-body oxygen consumption rate at rest reflects increased electron transport through the respiratory chain, driven by a decreased phosphorylation potential. The increased electron transport rate may compensate for the decreased efficiency of oxidative phosphorylation (phosphorylation potential).
Roef
M J
MJ
Department of Pediatric Gastroenterology, University Children's Hospital, Utrecht, The Netherlands.
Reijngoud
D-J
DJ
Jeneson
J A L
JA
Berger
R
R
de Meer
K
K
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000328:Adult; D016001:Confidence Intervals; D042967:Electron Transport Complex I; D005080:Exercise Test / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008931:Mitochondria, Muscle / Q000201:enzymology; D009135:Muscular Diseases / Q000201:enzymology / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000172:deficiency*; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000502:physiology*
D000244:Adenosine Diphosphate; D009247:NADH, NADPH Oxidoreductases; D042967:Electron Transport Complex I