title: The effects of physiological fluctuation of serum potassium levels on excitability properties in healthy human motor axons.
abstract: OBJECTIVE
  Previous axonal excitability studies suggest hyperkalemia or hypokalemia can significantly alter membrane potential and thereby, excitability properties. We studied whether physiological fluctuation of serum potassium levels affects axonal excitability in normal human axons.
  
  
  METHODS
  Threshold tracking was used to measure strength-duration properties, refractory periods, supernormality, and threshold electrotonus in median motor axons of 12 normal volunteers. In each subject, the excitability indices and serum potassium levels were measured three times (baseline, 2h later, and 2 weeks later).
  
  
  RESULTS
  The pooled data (n=36) showed significant correlation of the relative refractory period, supernormality, and depolarizing threshold electrotonus with potassium levels. Among each trial (12 subjects) the correlation did not reach statistical significance occasionally. Strength-duration properties, refractoriness, late subnormality, and hyperpolarizing threshold electrotonus were not significantly affected by serum potassium levels.
  
  
  CONCLUSIONS
  Even in the normal range, serum potassium levels could slightly alter axonal excitability of human axons. Among excitability indices, the relative refractory period, supernormality, and threshold electrotonus are sensitive to potassium levels.
  
  
  CONCLUSIONS
  Physiological fluctuation of serum potassium levels could partly be responsible for inter- and intra-subject variability of excitability indices.
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan. kuwabara-s@faculty.chiba-u.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kuwabara
authors.forename: Sonoko
authors.initials: S
authors.lastname: Misawa
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Kanai
authors.forename: Noriko
authors.initials: N
authors.lastname: Tamura
authors.forename: Miho
authors.initials: M
authors.lastname: Nakata
authors.forename: Setsu
authors.initials: S
authors.lastname: Sawai
authors.forename: Takamichi
authors.initials: T
authors.lastname: Hattori
mesh_terms: D000328:Adult; D001369:Axons / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D011188:Potassium / Q000097:blood*; D012016:Reference Values
chemical_list: D011188:Potassium