Titre :
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Resting Ca2+ influx and potential role of TRPC channels investigated by MN2+ quenching of FURA-2 fluorescence and gene transfer in mammalian skeletal muscle fibres under voltage control
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contenu dans :
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Auteurs :
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Congrès international de myologie 2008 (International Congress of Myology 2008; 26-30 mai 2008; Marseille, France) ;
Berbey C ;
Weiss N ;
Legrand C ;
Allard B
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Type de document :
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Article
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Année de publication :
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2008
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Pages :
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p. 128
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Langues:
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Anglais
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Mots-clés :
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canal calcium
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canal cationique TRPC
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colloque
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courant calcique
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dystrophie musculaire de Duchenne
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électrodiagnostic
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fibre musculaire isolée
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manganèse
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muscle squelettique
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physiopathologie
;
souris
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Résumé :
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A Ca2+ influx is known to occur in skeletal muscle cells at rest. The study of this influx is of primordial interest since an exacerbated resting Ca2+ entry has been considered to represent an early step associated with the pathophysiological changes in dystrophin-deficient muscles. Single channel recordings have revealed the existence of Ca2+ channels open at rest that could correspond to TRPC channels since repression of expression of these channels led to a reduction of channel activity. At the macroscopic level, the passive entry of Ca2+ has been essentially monitored using the Mn2+ quenching method but this was always performed in the absence of voltage control of the cell and therefore it was not established whether Mn2+ entry generates a measurable macroscopic membrane current consistent with the existence of Ca2+ permeable ion channels open at rest. The aim of the present study was to investigate resting Ca2+ influx using the method of Mn2+ quenching of fura-2 fluorescence on enzymatically isolated mouse muscle cells under voltage control and the potential role of TRPC1 in this influx using an overexpression strategy. The rate of quenching of fura-2 fluorescence induced by substitution of Mn2+ for external Mg2+ was found to be dependent on the external [Mn2+] and on the cell membrane potential. Replacement of Mn2+ by Mg2+ gave rise to an outward current at -80 mV associated with an increase in the input resistance. Calibration of the fura-2 response in ionomycine-permeabilized cells indicated that the Mn2+ influx is too minute to be resolved as a macroscopic current. In cells overexpressing TRPC1 channels after gene transfer by electroporation, resting potential, action potentials, resting conductance and Mn2+ quenching rate of fura-2 were found to be unchanged. The possibility that TRPC1 channels are involved in other steps of muscle Ca2+ handling is currently explored.
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