Roles of ryanodine and inositol triphosphate receptors in regulation of plateau potentials in turtle spinal motoneurons.
Generation of plateau potentials in spinal motoneurons depends on activation of voltage sensitive L-type Ca(2+) channels. These channels are facilitated by metabotropic receptors known to promote release of Ca(2+) from intracellular stores. The aim of this study is to determine if Ca(2+)-release receptors in the endoplasmic reticulum (ER) that are sensitive to ryanodine (RyRs) and to inositol triphosphate receptors (IP(3)Rs) contribute to the generation of plateau potentials. The effects of antagonists to RyRs, IP(3)Rs and phospholipase C (PLC) were tested on discharge patterns associated with plateau potentials in motoneurons in slices from the spinal cord of the turtle. Plateau-related discharge patterns, un-facilitated or facilitated by agonists for group I glutamate metabotropic receptors, muscarine-sensitive cholinergic receptors or L-type Ca(2+) channels were inhibited by blockade of RyRs. In contrast, antagonists of IP(3)Rs or PLC preferentially inhibited plateau-related discharge patterns when facilitated by activation of metabotropic receptors but in only half of the cells when promoted in the absence of metabotropic facilitators. Our findings show that RyRs and IP(3)Rs regulate the generation of plateau potentials in motoneurons and suggest that RyRs may be directly involved with activation of the plateau potential.
Mejia-Gervacio
S
S
Dept. de Neurobiología Celular y Molecular, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Apartado Postal 1-1141, Juriquilla, Querétaro, Mexico. mejiag@calli.inb.unam.mx
Hounsgaard
J
J
Diaz-Muñoz
M
M
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology*; D014426:Turtles
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester