The effects of physiological fluctuation of serum potassium levels on excitability properties in healthy human motor axons.
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.
Kuwabara
Satoshi
S
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
Misawa
Sonoko
S
Kanai
Kazuaki
K
Tamura
Noriko
N
Nakata
Miho
M
Sawai
Setsu
S
Hattori
Takamichi
T
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
D011188:Potassium