An M-like outward current regulates the excitability of spinal motoneurones in the adult turtle.
The excitatory action of muscarine on spinal motoneurones was investigated with intracellular recordings in a slice preparation from adult turtles. In these cells muscarine is known to facilitate a persistent inward current mediated by L-type Ca(2+) channels. When this effect was blocked by nifedipine, muscarine still increased the excitability. In voltage clamp, a slowly activating outward current, generated during depolarizing voltage commands and deactivating as a tail current on return to the holding voltage, was reduced by muscarine. This outward current was activated when the voltage was stepped to potentials positive to -60 mV, was voltage sensitive and had a deactivation time constant of approximately 80 ms. These findings are compatible with an M-current. This possibility was also supported by the finding that the current was reduced by XE-991 - a selective blocker of the KCNQ potassium channels underlying M-currents in other cell types. Our findings suggest that an M-like current, mediated by a KCNQ channel, contributes to the intrinsic response properties of motoneurones in the adult spinal cord by increasing adaptation of repetitive firing and decreasing the slope of the frequency-current relation.
Alaburda
Aidas
A
Department of Medical Physiology, Panum Institute, University of Copenhagen, Copenhagen N. DK 2200, Denmark.
Perrier
Jean-François
JF
Hounsgaard
Jørn
J
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009116:Muscarine / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011930:Reaction Time; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D013331:Strychnine / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014426:Turtles
C112297:10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone; D000873:Anthracenes; D020746:Calcium Channels, L-Type; D011976:Receptors, Muscarinic; D013779:Tetrodotoxin; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D001285:Atropine; D009116:Muscarine; D013331:Strychnine; D009543:Nifedipine