Facilitation of plateau potentials in turtle motoneurones by a pathway dependent on calcium and calmodulin.
1. The involvement of intracellular calcium and calmodulin in the modulation of plateau potentials in motoneurones was investigated using intracellular recordings from a spinal cord slice preparation. 2. Chelation of intracellular calcium with BAPTA-AM or inactivation of calmodulin with W-7 or trifluoperazine reduced the amplitude of depolarization-induced plateau potentials. Inactivation of calmodulin also inhibited facilitation of plateau potentials by activation of group I metabotropic glutamate receptors or muscarinic receptors. 3. In low-sodium medium and in the presence of tetraethylammonium and tetrodotoxin, calcium action potentials evoked by depolarization were followed by a short hyperpolarization ascribed to the calcium-activated non-selective cationic current (ICAN) and by a dihydropyridine-sensitive afterdepolarization. The amplitude of the afterdepolarization depended on the number of calcium spikes and was mediated by L-type calcium channels. 4. The dihydropyridine-sensitive afterdepolarization induced by calcium spikes was reduced by blockade of calmodulin. 5. It is proposed that plateau potentials in spinal motoneurones are facilitated by activation of a calcium-calmodulin-dependent pathway.
Perrier
J F
JF
Department of Medical Physiology, Panum Institute, University of Copenhagen, DK 2200 Copenhagen N, Denmark.
Mejia-Gervacio
S
S
Hounsgaard
J
J
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives*; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology; D014426:Turtles
D020746:Calcium Channels, L-Type; D002147:Calmodulin; D018492:Dopamine Antagonists; D018094:Receptors, Metabotropic Glutamate; D011976:Receptors, Muscarinic; C104077:metabotropic glutamate receptor type 1; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D014268:Trifluoperazine; D013779:Tetrodotoxin; D004533:Egtazic Acid; D019789:Tetraethylammonium; D012964:Sodium; D002118:Calcium