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Suprachiasmatic Nucleus Neurons Are Glucose Sensitive

Department of Psychology, Smith College, Northampton, MA 01063

Roselle M. Hoffmaster

Department of Psychology, Smith College, Northampton, MA 01063

Edra L. Stern

Department of Psychology, Smith College, Northampton, MA 01063

Mary E. Harrington

Department of Psychology, Smith College, Northampton, MA 01063

David Bickar

Department of Biochemistry, Smith College, Northampton, MA 01063

The suprachiasmatic nucleus (SCN) in the hypothalamus serves as the pacemaker for mammalian circadian rhythms. In a hamster brain slice preparation, the authors were able to record spontaneous activity from SCN cells for up to 4 days in vitro and verify a self-sustained rhythm in firing. The phase of this rhythm was altered by the concentration of glucose in the bathing medium, with time of peak firing advanced for a 20 mM glucose condition and slightly delayed for a 5 mM glucose condition, relative to 10 mM. The advancing effect of 20 mM glucose and the delaying effect of 5 mM glucose were not maintained during a 2nd day in vitro after changing the bathing medium back to 10 mM glucose, thus indicating the effect was not a permanent phase shift of the underlying oscillation. In experiments recording from cell-attached membrane patches on acutely dissociated hamster SCN neurons, exchanging the bathing medium from high (20 mM) to zero glucose increased potassium (K⁺)-selective channel activity With inside-out membrane patches, the authors revealed the presence of a glybenclamide-sensitive K⁺ channel (190 pS) and a larger conductance (260 pS) Ca²⁺- dependent K⁺ channel that were both reversibly inhibited by ATP at the cytoplasmic surface. Furthermore, 1 mM tetraethylammonium chloride was demonstrated to advance peak firing time in the brain slice in a similar manner to a high concentration of glucose (20 mM). The authors interpret the results to imply that SCNs are sensitive to glucose, most probably via ATP modulation of K⁺ channel activity in these neurons. Tonic modulation of K⁺ channel activity appears to alter output of the pacemaker but does not reset the phase.

Key Words: ATP • brain slice • ATP-sensitive K+ channel • calcium-dependent K+ channel • circadian • glucose • suprachiasmatic

Journal of Biological Rhythms, Vol. 12, No. 5, 388-400 (1997)
DOI: 10.1177/074873049701200501


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