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  • Title: Axonal hyperpolarization associated with acute hypokalemia: multiple excitability measurements as indicators of the membrane potential of human axons.
    Author: Kuwabara S, Kanai K, Sung JY, Ogawara K, Hattori T, Burke D, Bostock H.
    Journal: Muscle Nerve; 2002 Aug; 26(2):283-7. PubMed ID: 12210395.
    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.
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