Calcium content and respiratory control index of skeletal muscle
mitochondria during exercise and recovery.
Madsen, Klavs, Per Ertbjerg, Mogens Stig Djurhuus, and Preben K.
Pedersen.
Department of Physical Education, Odense University, Denmark,
Department of Clinical Chemistry, Odense University Hospital,
Denmark
APStracts 3:0182E, 1996.
The purpose of this study was to evaluate the relationship between
mitochondrial Ca2+ concentration and the respiratory control index
(RCI; state III/state IV) in isolated mitochondria before, and after
exhaustive exercise at 75% of VO2max. Muscle biopsies of 100 to 150
mg from 12 moderately trained men were sampled at rest, immediately
after exercise, and 30 min or 60 min after exercise. The
mitochondrial Ca2+ content following exhaustive exercise was
significantly higher than the pre-exercise level (15.1, range 39.4 vs
11.6, range 6.5 nmol/mg protein, respectively; P<0.05), and RCI
increased from 11.6 (range 14.4) at rest to 13.7 (range 15.0) at
exhaustion (P<0.05). Following 60 min of recovery, the
mitochondrial Ca2+ content was still high (18.8, range 29.9 nmol/mg
protein), but the RCI value was significantly depressed due to
increased state IV value and, in fact, lower than the pre-exercise
value (8.6, range 5.1; P<0.05). Our results show that the
mitochondrial Ca2+ content is increased in human skeletal muscle
following prolonged exhaustive exercise and this is followed by an
elevated RCI value with slightly increased state III and decreased
state IV respiration. The restoration of the elevated mitochondrial
Ca2+ level is slow and could be related to an increased state IV
respiration which indicate Ca2+ uncoupled respiration during
recovery.
Received 2 October 1995; accepted in final form 29 July 1996.
APS Manuscript Number E479-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996