Differential regulation of two distinct voltage-dependent sodium currents by group III metabotropic glutamate receptor activation in insect pacemaker neurons.
Using whole cell patch-clamp technique and immunocytochemistry on adult dorsal unpaired median (DUM) neurons isolated from the cockroach Periplaneta americana CNS, we reported the characterization of a native mGluR, sharing pharmacological properties with vertebrate metabotropic glutamate receptor III (mGluRIII) that regulated voltage-dependent sodium current (I(Na)). The global I(Na) was dissociated by means of l-glutamate sensitivity, deactivation time constant, voltage dependence of activation and inactivation, recovery from inactivation, and intracellular regulation process. These two currents were respectively designated I(Na1) and I(Na2) for l-glutamate-sensitive and -insensitive sodium currents. l-glutamate selectively reduced I(Na1) by an increase of intracellular cAMP level. Using different activators and/or inhibitors of G proteins and cAMP/PKA cascade, together with St-Ht31 (an inhibitor of PKA binding to AKAP) and AKAP-79 antibodies, we established that mGluRIII was linked to I(Na1) by a Gi/o and a suspected Gs protein. According to the activated signaling pathway, l-glutamate elevated the cAMP level, which thereby activated cytosolic PKA and released PKA bound to AKAP. As expected from both biophysical and pharmacological studies, we showed that, through an inhibition of I(Na1), l-glutamate increased DUM neuron spontaneous electrical activity. These results indicated that such mGluRIII-activated dual processes provided a new physiological control of pacemaker neuronal firing.
Lavialle-Defaix
Céline
C
Laboratoire Récepteurs et Canaux Ioniques Membranaires, UPRES EA 2647, Université d'Angers, UFR Sciences, 2 Boulevard Lavoisier, F-49045 Angers cedex, France.
Gautier
Hélène
H
Defaix
Antoine
A
Lapied
Bruno
B
Grolleau
Françoise
F
D000465:Algorithms; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002469:Cell Separation; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D004594:Electrophysiology; D018698:Glutamic Acid / Q000494:pharmacology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010526:Periplaneta / Q000502:physiology*; D037342:Pertussis Toxin / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers; D018094:Receptors, Metabotropic Glutamate; D015222:Sodium Channels; C102718:metabotropic glutamate receptor 3; D005576:Colforsin; D018698:Glutamic Acid; D000242:Cyclic AMP; D037342:Pertussis Toxin