title: Daily rhythmicity of large-conductance Ca2+ -activated K+ currents in suprachiasmatic nucleus neurons.
abstract: Neurons within the suprachiasmatic nucleus (SCN) comprise the master circadian pacemaker in mammals. These neurons exhibit circadian rhythms in spontaneous action potential frequency and in the transcription of core circadian clock genes, including Period1 (Per1). Targeted electrophysiological recordings from SCN neurons marked with a green fluorescent protein (GFP) reporter of Per1 gene transcription have previously indicated that K(+) currents are critically involved in the expression of neurophysiological rhythmicity. The present study examined the role of large conductance, Ca(2+)-activated K(+) channels (BK) in the daily rhythmicity of mouse SCN neurons. BK-mediated currents were examined in Per1::GFP neurons under voltage clamp using iberiotoxin, a specific BK channel blocker. BK current was a greater proportion of whole-cell outward currents during the night than during the day. Analysis of iberiotoxin difference currents also demonstrated that BK current amplitude and density were greater during the night and that the day/night difference in steady state amplitude was not due to altered inactivation. Single cell RT-PCR demonstrated the presence of the BK channel transcript, KCNMA1, in Per1-expressing neurons. In situ hybridization analysis further showed that KCNMA1 mRNA was rhythmically expressed in the SCN under light:dark (LD) conditions, peaking during the middle of the night phase. Acute inhibition of BK currents blunted the circadian rhythm SCN neuron spike frequency. These results establish that BK channel function is elevated at night, thus altering SCN neuron activity.
authors.affiliation: Department of Biological Sciences, Vanderbilt University, VU Station B, Box 35-1634, Nashville, TN 37235-1634, USA.
authors.forename: Gilbert R
authors.initials: GR
authors.lastname: Pitts
authors.forename: Hidenobu
authors.initials: H
authors.lastname: Ohta
authors.forename: Douglas G
authors.initials: DG
authors.lastname: McMahon
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D000704:Analysis of Variance; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D015870:Gene Expression / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D017403:In Situ Hybridization / Q000379:methods; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D009687:Nuclear Proteins / Q000235:genetics; D018408:Patch-Clamp Techniques / Q000379:methods; D010455:Peptides / Q000494:pharmacology; D056950:Period Circadian Proteins; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013493:Suprachiasmatic Nucleus / Q000166:cytology*
chemical_list: D018797:Cell Cycle Proteins; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009687:Nuclear Proteins; D010455:Peptides; C539023:Per1 protein, mouse; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D002104:Cadmium; D049452:Green Fluorescent Proteins; C064719:iberiotoxin