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1 Medical Biophysics, Institute of Physiology and Pathophysiology, INF 326, Ruprecht-Karls-University, 69120 Heidelberg, Germany2 Department of Physiology, Catholic University of Louvain, 1200 Bruxelles, Belgium3 Department of Neurology, University of Washington, Seattle, WA, USA
L-type calcium currents (iCa) were recorded using the two-microelectrode voltage-clamp technique in single short toe muscle fibres of three different mouse strains: (i) C57/SV129 wild-type mice (wt); (ii) mdx mice (an animal model for Duchenne muscular dystrophy; and (iii) transgenically engineered mini-dystrophin (MinD)-expressing mdx mice. The activation and inactivation properties of iCa were examined in 2- to 18-month-old animals. Ca2+ current densities at 0 mV in mdx fibres increased with age, but were always significantly smaller compared to age-matched wild-type fibres. Time-to-peak (TTP) of iCa was prolonged in mdx fibres compared to wt fibres. MinD fibres always showed similar TTP and current amplitudes compared to age-matched wt fibres. In all three genotypes, the voltage-dependent inactivation and deactivation of iCa were similar. Intracellular resting calcium concentration ([Ca2+]i) and the distribution of dihydropyridine binding sites were also not different in young animals of all three genotypes, whereas iCa was markedly reduced in mdx fibres. We conclude, that dystrophin influences L-type Ca2+ channels via a direct or indirect linkage which may be disrupted in mdx mice and may be crucial for proper excitation–contraction coupling initiating Ca2+ release from the sarcoplasmic reticulum. This linkage seems to be fully restored in the presence of mini-dystrophin.
(Received 1 September 2003;
accepted after revision 27 October 2003;
first published online 31 October 2003)
Corresponding author R. H. A. Fink: Medical Biophysics, Institute of Physiology and Pathophysiology, INF 326, Ruprecht-Karls-University, 69120 Heidelberg, Germany. Email: rainer.fink{at}urz.uni-heidelberg.de
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