The calcium homeostasis and the membrane potential of cultured muscle cells from patients with myotonic dystrophy.
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.
Jacobs
A E
AE
Department of Biochemistry, University of Nijmegen, The Netherlands.
Benders
A A
AA
Oosterhof
A
A
Veerkamp
J H
JH
van Mier
P
P
Wevers
R A
RA
Joosten
E M
EM
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
D015220:Calcium Channels; D009543:Nifedipine; D000109:Acetylcholine; D002118:Calcium