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February 1972

Penicillin-Induced Segmental Myoclonus: II. Membrane Properties of Cat Spinal Motoneurons

Author Affiliations

From the departments of medicine (Drs. Kao and Crill) and physiology and biophysics (Dr. Crill), Division of Neurology, University of Washington School of Medicine, Seattle.

Arch Neurol. 1972;26(2):162-168. doi:10.1001/archneur.1972.00490080080009

Penicillin was applied to the cat spinal cord and the changes in membrane properties of motoneurons measured. Just prior to the appearance of the facilitated spontaneous synaptic potentials, there is a diminution of the resting potential of the motoneuron. This is not associated with a detectable change in membrane resistance or in time constant. The after-hyperpolarization of the action potential is decreased. The simplest explanation for these changes is a change in the potassium equilibrium potential (Ek). To test the possibility that the change in Ek is causally related to the appearance of the prolonged depolarization, the intracellular potassium of normal motoneurons was displaced with either choline or tetramethylammonium ions. In both cases a prolonged depolarization occurred similar to that produced by penicillin, and, moreover, this response was evoked by directly applied intracellular currents.

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