title: Slow calcium signals after tetanic electrical stimulation in skeletal myotubes.
abstract: The fluorescent calcium signal from rat myotubes in culture was monitored after field-stimulation with tetanic protocols. After the calcium signal sensitive to ryanodine and associated to the excitation-contraction coupling, a second long-lasting calcium signal refractory to ryanodine was consistently found. The onset kinetics of this slow signal were slightly modified in nominally calcium-free medium, as were both the frequency and number of pulses during tetanus. No signal was detected in the presence of tetrodotoxin. The participation of the dihydropyridine receptor (DHPR) as the voltage sensor for this signal was assessed by treatment with agonist and antagonist dihydropyridines (Bay K 8644 and nifedipine), showing an enhanced and inhibitory response, respectively. In the dysgenic GLT cell line, which lacks the alpha1(S) subunit of the DHPR, the signal was absent. Transfection of these cells with the alpha1(S) subunit restored the slow signal. In myotubes, the inositol 1,4,5-trisphosphate (IP(3)) mass increase induced by a tetanus protocol preceded in time the slow calcium signal. Both an IP(3) receptor blocker and a phospholipase C inhibitor (xestospongin C and U73122, respectively) dramatically inhibit this signal. Long-lasting, IP(3)-generated slow calcium signals appear to be a physiological response to activity-related fluctuations in membrane potential sensed by the DHPR.
authors.affiliation: Centro de Estudios Moleculares de la Célula, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
authors.forename: José M
authors.initials: JM
authors.lastname: Eltit
authors.forename: Jorge
authors.initials: J
authors.lastname: Hidalgo
authors.forename: José L
authors.initials: JL
authors.lastname: Liberona
authors.forename: Enrique
authors.initials: E
authors.lastname: Jaimovich
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004594:Electrophysiology / Q000379:methods*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D007091:Image Processing, Computer-Assisted; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D047028:Macrocyclic Compounds; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D012433:Ryanodine / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D004963:Estrenes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D047028:Macrocyclic Compounds; D010080:Oxazoles; D011760:Pyrrolidinones; D018160:Receptors, Cytoplasmic and Nuclear; C108644:xestospongin A; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D012433:Ryanodine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D010738:Type C Phospholipases; D009543:Nifedipine; D002118:Calcium