AJP - Cell Physiology, Vol 237, Issue 3 131-C136, Copyright © 1979 by American Physiological Society
Suppression of myotonia in dystrophic chicken muscle by phenytoin
R. K. Entrikin and S. H. Bryant
We describe myotonic electromyographic activity in muscles of genetically
dystrophic chickens and show that this activity is antagonized in vivo by
doses of phenytoin (DPH) that improve righting ability. To test the
possibility that the in vivo effects of DPH can be accounted for by a
direct action on skeletal muscle we studied posterior latissimus dorsi
fibers in vitro at 23 degrees C with intracellular microelectrodes.
Compared to normal fibers, fibers from untreated dystrophic chicks had
larger diameters, increased membrane capacitance, longer latencies at
rheobase, and a greater tendency to fire repetitively in response to direct
stimulation. DPH (10 or 50 micrograms/ml in the bath solution) decreased
latencies at rheobase and repetitive firing in fibers from untreated
chicks. In DPH-free solution fibers from dystrophic chicks treated
chronically with DPH were still abnormal with respect to latencies at
rheobase and ease of repetitive firing. The data support the hypothesis
that abnormalities of membrane electrical properties are major features of
dystrophic chicken muscles and furthermore, show that DPH suppresses, but
does not abolish, these abnormalities.
