Norepinephrine activates potassium conductance in neurons of the turtle cerebral cortex.
Whole-cell voltage and current clamp recordings were obtained from cortical neurons of the pond turtle, Pseudemys scripta elegans. Norepinephrine (NE) induced an outward current in 50% of pyramidal neurons. This current had a reversal potential of -88.3 +/- 3.2 mV, consistent with a K+ conductance increase, and had a mean amplitude of 18.3 +/- 7.2 pA at -40 mV. The ionic dependence and pharmacological analyses are both consistent with alpha 2 adrenergic receptor stimulation. Inhibition of Na(+)-dependent action potentials with TTX did not diminish the NE-induced K+ conductance, indicating that NE acts directly on the postsynaptic neuron. In addition to effects on postsynaptic conductance, NE dramatically decreased the amplitude of spontaneous inhibitory postsynaptic currents (IPSCs) in 55% of pyramidal neurons. The decrease in spontaneous IPSCs was observed both in those neurons which exhibited an increase in K+ conductance in response to NE administration (81%) and in those which did not (33%). Thus, NE modulates neuronal excitability both directly by activating a postsynaptic K+ conductance and indirectly by decreasing spontaneous IPSCs.
Blanton
K J
KJ
Department of Neurology and Neurological Sciences, Stanford University School of Medicine, CA 94305.
Kriegstein
A R
AR
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects*; D004553:Electric Conductivity / Q000187:drug effects; D005071:Evoked Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D011188:Potassium / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014426:Turtles / Q000502:physiology*
D013779:Tetrodotoxin; D011188:Potassium; D009638:Norepinephrine