title: Axonal hyperpolarization associated with acute hypokalemia: multiple excitability measurements as indicators of the membrane potential of human axons.
abstract: Multiple nerve excitability measurements have been proposed for clinical testing of nerve function, and an important determinant of excitability is membrane potential. We report a patient with acquired hypokalemic paralysis in whom multiple excitability indices (stimulus-response curve, strength-duration properties, threshold electrotonus, recovery cycle) were measured during and after an acute hypokalemic attack (serum K(+) level, 2.1 mEq/L and 4.5 mEq/L, respectively). During hypokalemia, there was a shift of the stimulus-response curve to the right, a decrease in strength-duration time constant, a "fanning-out" of responses during threshold electrotonus, a reduction in relative refractory period, and an increase in superexcitability; all of these indicate axonal hyperpolarization, presumably due to the K(+) equilibrium potential being more negative. These indices returned to normal 20 h later, associated with normalization of the serum K(+) level. These results demonstrate that the changes associated with hypokalemic paralysis are not confined to muscle and that axons undergo hyperpolarization in vivo. Multiple excitability measurements can be used as a tool to identify changes in membrane potential of human axons.
authors.affiliation: Department of Neurology, Chiba University School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan. kuwabara@med.m.chiba-u.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kuwabara
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Kanai
authors.forename: Jia-Ying
authors.initials: JY
authors.lastname: Sung
authors.forename: Kazue
authors.initials: K
authors.lastname: Ogawara
authors.forename: Takamichi
authors.initials: T
authors.lastname: Hattori
authors.forename: David
authors.initials: D
authors.lastname: Burke
authors.forename: Hugh
authors.initials: H
authors.lastname: Bostock
mesh_terms: D000200:Action Potentials; D000208:Acute Disease; D000328:Adult; D001369:Axons / Q000502:physiology*; D004558:Electric Stimulation; D004568:Electrodiagnosis / Q000379:methods; D006801:Humans; D020514:Hypokalemic Periodic Paralysis / Q000175:diagnosis* / Q000503:physiopathology*; D008297:Male; D008475:Median Nerve / Q000166:cytology / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D009129:Muscle Tonus / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D013979:Tibial Nerve / Q000166:cytology / Q000502:physiology; D014459:Ulnar Nerve / Q000166:cytology / Q000502:physiology