title: Voltage-Independent Inhibition of the Tetrodotoxin-Sensitive Sodium Currents by Oxotremorine and Angiotensin II in Rat Sympathetic Neurons.
abstract: Tetrodotoxin-sensitive Na(+) currents have been extensively studied because they play a major role in neuronal firing and bursting. In this study, we showed that voltage-dependent Na(+) currents are regulated in a slow manner by oxotremorine (oxo-M) and angiotensin II in rat sympathetic neurons. We found that these currents can be readily inhibited through a signaling pathway mediated by G proteins and phospholipase C (PLC) β1. This inhibition is slowly established, pertussis toxin-insensitive, partially reversed within tens of seconds after oxo-M washout, and not relieved by a strong depolarization, suggesting a voltage-insensitive mechanism of inhibition. Specificity of the M1 receptor was tested by the MT-7 toxin. Activation and inactivation curves showed no shift in the voltage dependency under the inhibition by oxo-M. This inhibition is blocked by a PLC inhibitor (U73122, 1-(6-{[(17β)-3-Methoxyestra-1,3,5(10)-trien-17-yl]amino}hexyl)-1H-pyrrole-2,5-dione), and recovery from inhibition is prevented by wortmannin, a PI3/4 kinase inhibitor. Hence, the pathway involves Gq/11 and is mediated by a diffusible second messenger. Oxo-M inhibition is occluded by screening phosphatidylinositol 4,5-bisphosphate (PIP2)-negative charges with poly-l-lysine and prevented by intracellular dialysis with a PIP2 analog. In addition, bisindolylmaleimide I, a specific ATP-competitive protein kinase C (PKC) inhibitor, rules out that this inhibition may be mediated by this protein kinase. Furthermore, oxo-M-induced suppression of Na(+) currents remains unchanged when neurons are treated with calphostin C, a PKC inhibitor that targets the diacylglycerol-binding site of the kinase. These results support a general mechanism of Na(+) current inhibition that is widely present in excitable cells through modulation of ion channels by specific G protein-coupled receptors.
authors: Department of Physiology, School of Medicine, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico (E.I.P., L.D.C., I.A., D.E.G.), and Section of Bioelectronics, Department of Electrical Engineering, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico (D.E.-V.).
authors: Erika I
authors: EI
authors: Puente
authors: Department of Physiology, School of Medicine, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico (E.I.P., L.D.C., I.A., D.E.G.), and Section of Bioelectronics, Department of Electrical Engineering, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico (D.E.-V.).
authors: Lizbeth
authors: L
authors: De la Cruz
authors: Department of Physiology, School of Medicine, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico (E.I.P., L.D.C., I.A., D.E.G.), and Section of Bioelectronics, Department of Electrical Engineering, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico (D.E.-V.).
authors: Isabel
authors: I
authors: Arenas
authors: Department of Physiology, School of Medicine, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico (E.I.P., L.D.C., I.A., D.E.G.), and Section of Bioelectronics, Department of Electrical Engineering, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico (D.E.-V.).
authors: David
authors: D
authors: Elias-Viñas
authors: Department of Physiology, School of Medicine, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico (E.I.P., L.D.C., I.A., D.E.G.), and Section of Bioelectronics, Department of Electrical Engineering, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico (D.E.-V.). erasmo@unam.mx.
authors: David E
authors: DE
authors: Garcia
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D005728:Ganglia, Sympathetic / Q000187:drug effects / Q000502:physiology; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010095:Oxotremorine / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000502:physiology*; D017783:Superior Cervical Ganglion / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology*
chemical_list: D026941:Sodium Channel Blockers; D015222:Sodium Channels; D000804:Angiotensin II; D013779:Tetrodotoxin; D010095:Oxotremorine