Involvement of inositol 1,4,5-trisphosphate in nicotinic calcium responses in dystrophic myotubes assessed by near-plasma membrane calcium measurement.
In skeletal muscle cells, plasma membrane depolarization causes a rapid calcium release from the sarcoplasmic reticulum through ryanodine receptors triggering contraction. In Duchenne muscular dystrophy (DMD), a lethal disease that is caused by the lack of the cytoskeletal protein dystrophin, the cytosolic calcium concentration is known to be increased, and this increase may lead to cell necrosis. Here, we used myotubes derived from control and mdx mice, the murine model of DMD, to study the calcium responses induced by nicotinic acetylcholine receptor stimulation. The photoprotein aequorin was expressed in the cytosol or targeted to the plasma membrane as a fusion protein with the synaptosome-associated protein SNAP-25, thus allowing calcium measurements in a restricted area localized just below the plasma membrane. The carbachol-induced calcium responses were 4.5 times bigger in dystrophic myotubes than in control myotubes. Moreover, in dystrophic myotubes the carbachol-mediated calcium responses measured in the subsarcolemmal area were at least 10 times bigger than in the bulk cytosol. The initial calcium responses were due to calcium influx into the cells followed by a fast refilling/release phase from the sarcoplasmic reticulum. In addition and unexpectedly, the inositol 1,4,5-trisphosphate receptor pathway was involved in these calcium signals only in the dystrophic myotubes. This surprising involvement of this calcium release channel in the excitation-contraction coupling could open new ways for understanding exercise-induced calcium increases and downstream muscle degeneration in mdx mice and, therefore, in DMD.
Pharmacology Laboratory, School of Pharmacy, University of Lausanne-Geneva, 1211 Geneva, Switzerland.
Olivier
O
Basset
François-Xavier
FX
Boittin
Olivier M
OM
Dorchies
Jean-Yves
JY
Chatton
Cornelis
C
van Breemen
Urs T
UT
Ruegg
D000331:Aequorin / Q000737:chemistry; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D018679:Cholinergic Agonists / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D009336:Necrosis; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25; D013997:Time Factors; D014162:Transfection
D015220:Calcium Channels; D018679:Cholinergic Agonists; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D018160:Receptors, Cytoplasmic and Nuclear; D011978:Receptors, Nicotinic; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D049452:Green Fluorescent Proteins; D000331:Aequorin; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D002118:Calcium