A sodium-pump-mediated afterhyperpolarization in pyramidal neurons.
The sodium-potassium ATPase (i.e., the "sodium pump") plays a central role in maintaining ionic homeostasis in all cells. Although the sodium pump is intrinsically electrogenic and responsive to dynamic changes in intracellular sodium concentration, its role in regulating neuronal excitability remains unclear. Here we describe a physiological role for the sodium pump in regulating the excitability of mouse neocortical layer 5 and hippocampal CA1 pyramidal neurons. Trains of action potentials produced long-lasting (∼20 s) afterhyperpolarizations (AHPs) that were insensitive to blockade of voltage-gated calcium channels or chelation of intracellular calcium, but were blocked by tetrodotoxin, ouabain, or the removal of extracellular potassium. Correspondingly, the AHP time course was similar to the decay of activity-induced increases in intracellular sodium, whereas intracellular calcium decayed at much faster rates. To determine whether physiological patterns of activity engage the sodium pump, we replayed in vitro a place-specific burst of 15 action potentials recorded originally in vivo in a CA1 "place cell" as the animal traversed the associated place field. In both layer 5 and CA1 pyramidal neurons, this "place cell train" generated small, long-lasting AHPs capable of reducing neuronal excitability for many seconds. Place-cell-train-induced AHPs were blocked by ouabain or removal of extracellular potassium, but not by intracellular calcium chelation. Finally, we found calcium contributions to the AHP to be temperature dependent: prominent at room temperature, but largely absent at 35°C. Our results demonstrate a previously unappreciated role for the sodium-potassium ATPase in regulating the excitability of neocortical and hippocampal pyramidal neurons.
Department of Physiology and Neurobiology and Program in Experimental and Molecular Medicine, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756, USA. allan.gulledge@dartmouth.edu
Allan T
AT
Gulledge
Sameera
S
Dasari
Keita
K
Onoue
Emily K
EK
Stephens
J Michael
JM
Hasse
Daniel
D
Avesar
D000200:Action Potentials / Q000502:physiology*; D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D001572:Benzofurans / Q000378:metabolism; D055592:Biophysical Phenomena / Q000187:drug effects; D019256:Cadmium Chloride / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000378:metabolism; D005260:Female; D005452:Fluoresceins / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D017397:Prefrontal Cortex / Q000166:cytology; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D026941:Sodium Channel Blockers / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D000814:Aniline Compounds; D001572:Benzofurans; D002712:Chlorides; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D005452:Fluoresceins; C503942:Oregon green 488 BAPTA-1; D026941:Sodium Channel Blockers; C061665:sodium-binding benzofuran isophthalate; D002586:Cesium; D013779:Tetrodotoxin; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; C028019:cesium chloride; D019256:Cadmium Chloride; D011188:Potassium