title: Intracellular Na(+) and metabolic modulation of Na/K pump and excitability in the rat suprachiasmatic nucleus neurons.
abstract: Na/K pump activity and metabolic rate are both higher during the day in the suprachiasmatic nucleus (SCN) that houses the circadian clock. Here we investigated the role of intracellular Na(+) and energy metabolism in regulating Na/K pump activity and neuronal excitability. Removal of extracellular K(+) to block the Na/K pump excited SCN neurons to fire at higher rates and return to normal K(+) to reactivate the pump produced rebound hyperpolarization to inhibit firing. In the presence of tetrodotoxin to block the action potentials, both zero K(+)-induced depolarization and rebound hyperpolarization were blocked by the cardiac glycoside strophanthidin. Ratiometric Na(+) imaging with a Na(+)-sensitive fluorescent dye indicated saturating accumulation of intracellular Na(+) in response to pump blockade with zero K(+). The Na(+) ionophore monensin also induced Na(+) loading and hyperpolarized the membrane potential, with the hyperpolarizing effect of monensin abolished in zero Na(+) or by pump blockade. Conversely, Na(+) depletion with Na(+)-free pipette solution depolarized membrane potential but retained residual Na/K pump activity. Cyanide inhibition of oxidative phosphorylation blocked the Na/K pump to depolarize resting potential and increase spontaneous firing in most cells, and to raise intracellular Na(+) levels in all cells. Nonetheless, the Na/K pump was incompletely blocked by cyanide but completely blocked by iodoacetate to inhibit glycolysis, indicating the involvement of both oxidative phosphorylation and glycolysis in fueling the Na/K pump. Together, the results indicate the importance of intracellular Na(+) and energy metabolism in regulating Na/K pump activity as well as neuronal excitability in the SCN neurons.
authors: Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Kwei-San, Tao-Yuan, Taiwan.
authors: Yi-Chi
authors: YC
authors: Wang
authors: Jyh-Jeen
authors: JJ
authors: Yang
authors: Rong-Chi
authors: RC
authors: Huang
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003486:Cyanides / Q000494:pharmacology; D005456:Fluorescent Dyes; D042541:Intracellular Space / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism*; D013327:Strophanthidin / Q000494:pharmacology; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D003486:Cyanides; D005456:Fluorescent Dyes; D013779:Tetrodotoxin; D013327:Strophanthidin; D008985:Monensin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium