Altered myoplasmic Ca(2+) handling in rat fast-twitch skeletal muscle fibres during disuse atrophy.
Pflugers Arch - Eur J Physiol. 2009-12-08; 459(4): 631-644
DOI: 10.1007/s00424-009-0764-x
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Weiss N(1), Andrianjafiniony T, Dupré-Aucouturier S, Pouvreau S, Desplanches D,
Jacquemond V.
Author information:
(1)Physiologie Intégrative Cellulaire et Moléculaire, Université Lyon 1, UMR
CNRS 5123, Bât. Raphaël Dubois, 43 boulevard du 11 novembre 1918, 69622,
Villeurbanne, France.
Calcium-dependent signalling pathways are believed to play an important role in
skeletal muscle atrophy, but whether intracellular Ca(2+) homeostasis is
affected in that situation remains obscure. We show here that there is a 20%
atrophy of the fast-type flexor digitorum brevis (FDB) muscle in rats hind limb
unloaded (HU) for 2 weeks, with no change in fibre type distribution. In
voltage-clamp experiments, the amplitude of the slow Ca(2+) current was found
similar in fibres from control and HU animals. In fibres loaded with the Ca(2+)
dye indo-1, the value for the rate of [Ca(2+)] decay after the end of
5-100-ms-long voltage-clamp depolarisations from -80 to +10 mV was found to be
30-50% lower in fibres from HU animals. This effect was consistent with a
reduced contribution of both saturable and non-saturable components of
myoplasmic Ca(2+) removal. However, there was no change in the relative amount
of parvalbumin, and type 1 sarco-endoplasmic reticulum Ca(2+)-ATPase was
increased by a factor of three in the atrophied muscles. Confocal imaging of
mitochondrial membrane potential showed that atrophied FDB fibres had
significantly depolarized mitochondria as compared to control fibres.
Depolarization of mitochondria in control fibres with carbonyl
cyanide-p-trifluoromethoxyphenylhydrazone induced a slowing of the decay of
[Ca(2+)] transients accompanied by an increase in resting [Ca(2+)] and a
reduction of the peak amplitude of the transients. Overall results provide the
first functional evidence for severely altered intracellular Ca(2+) removal
capabilities in atrophied fast-type muscle fibres and highlight the possible
contribution of reduced mitochondrial polarisation.
DOI: 10.1007/s00424-009-0764-x
PMID: 19997852 [Indexed for MEDLINE]