title: The calcium homeostasis and the membrane potential of cultured muscle cells from patients with myotonic dystrophy.
abstract: Using the fluorescence indicator, quin2, we compared the cytoplasmic Ca2+ concentration ([Ca2+]i) of cultured myotubes obtained from control subjects and myotonic dystrophy (MyD) patients. In Ca2(+)-free buffer the [Ca2+]i of the cultured MyD muscle cells was not significantly different from that of the control cells. In the presence of 1 mM external Ca2+ the cultured MyD muscle cells showed a significantly higher [Ca2+]i, which was due to the influx of Ca2+ through voltage-operated nifedipine-sensitive Ca2+ channels. In the presence of external Ca2+, MyD myotubes did not respond to acetylcholine, whereas control myotubes showed a transient increase in [Ca2+]i after addition of acetylcholine. This increase was inhibited by the addition of nifedipine. The differences in Ca2(+)-homeostasis between cultured MyD muscle cells and control cells were not due to differences in the resting membrane potential or the inability of the MyD cells to depolarize as a response to acetylcholine. Therefore, cultured MyD muscle cells exhibit altered nifedipine-sensitive voltage-operated channels which are active under conditions in which they are normally present in the inactive state, and which are unable to respond to depolarization caused by acetylcholine.
authors.affiliation: Department of Biochemistry, University of Nijmegen, The Netherlands.
authors.forename: A E
authors.initials: AE
authors.lastname: Jacobs
authors.forename: A A
authors.initials: AA
authors.lastname: Benders
authors.forename: A
authors.initials: A
authors.lastname: Oosterhof
authors.forename: J H
authors.initials: JH
authors.lastname: Veerkamp
authors.forename: P
authors.initials: P
authors.lastname: van Mier
authors.forename: R A
authors.initials: RA
authors.lastname: Wevers
authors.forename: E M
authors.initials: EM
authors.lastname: Joosten
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000328:Adult; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006706:Homeostasis; D006801:Humans; D008297:Male; D008564:Membrane Potentials; D008870:Microtubules / Q000187:drug effects / Q000502:physiology; D008875:Middle Aged; D009132:Muscles / Q000187:drug effects / Q000503:physiopathology*; D009136:Muscular Dystrophies / Q000503:physiopathology*; D009543:Nifedipine / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D009543:Nifedipine; D000109:Acetylcholine; D002118:Calcium