AJP - Cell Physiology, Vol 236, Issue 1 53-C57, Copyright © 1979 by American Physiological Society
Myasthenia in frogs immunized against cholinergic-receptor protein
W. L. Nastuk, W. D. Niemi, J. T. Alexander, H. W. Chang and M. A. Nastuk
Frogs immunized with cholinergic-receptor protein developed myasthenia in
116--175 days. The muscular weakness was overcome by subcutaneous
administration of 20 microgram of neostigmine. Electromyograms showed a
decline in action potential amplitude during a 2-Hz train. Nerve
stimulation evoked subthreshold end-plate potentials (EPPs) averaging 10.4
+/- 7.4 mV, but at many junctions no EPP was obtained. Miniature EPP
amplitude had a modal value of 0.15 mV compared with 0.35 mV for the
controls. The corresponding means were 0.24 +/- 0.23 mV and 0.48 +/- 0.23
mV. Microperfusion with edrophonium (5 mg/l) increased the amplitude of
EPPs and miniature end-plate potentials (MEPPS). Postjunctional response
tested with 20 muM carbamylcholine was 56% of control. Postjunctional
response by carbamylcholine iontophoresis gave 19 +/- 22 mV/nC compared
with 76 +/- 50 mV/nC for the controls. The data indicate that the
neuromuscular transmission deficits in receptor-immunized frogs are mainly
postsynaptic in origin, but there may be additional presynaptic
contributions. This amphibian model of myasthenia gravis offers many
opportunities and advantages in the study of receptor-immunized animals.
