AJP - Cell Physiology, Vol 263, Issue 4 C794-C802, Copyright © 1992 by American Physiological Society
Increase of apamin receptors in skeletal muscle induced by colchicine: possible role in myotonia
M. I. Behrens and C. Vergara
Centro de Estudios Cientificos de Santiago; Hospital Dr. Sotero del Rio, Chile.
We have shown an increase of apamin receptors in rat skeletal muscle
membranes following the application of colchicine to the sciatic nerve.
125I-apamin binding to partially purified membrane fractions was observed
since day 4, reached a maximum around days 6-15, and was negligible at day
35 after the application of colchicine. Control muscles (nerves treated
with buffer solution) showed low binding values (11 fmol/mg protein).
Maximal 125I-apamin binding values to partially purified muscle membranes
of colchicine-treated rats (42 fmol/mg protein) were lower than those
obtained in denervated muscle (95 fmol/mg protein). The affinity binding
constant values were 37 (colchicine) and 95 pM (denervation). No signs of
muscle denervation were observed on histological examination of the nerve
submitted to colchicine treatment nor in the muscles innervated by it.
Muscle tension developed by indirect stimulation was the same as in
controls. We here show also that partially purified membranes of normal
untreated muscles have measurable amounts of 125I-apamin binding (13
fmol/mg protein), similar to those obtained in control muscles.
Electromyographic recordings of the muscles after colchicine treatment of
the nerve showed abnormal repetitive electrical discharges, similar to
myotonic discharges, that were present with a similar temporal course as
the increase in apamin receptors. The myotonic-like discharges were
suppressed by the topical application of apamin to the muscle, whereas the
toxin had no effect on anthracene-9-carbolytic acid-induced myotonia. Our
results suggest that a neurotrophic factor that travels by axonal flow is
involved in the regulation of the expression of apamin receptors in
skeletal muscle membranes.(ABSTRACT TRUNCATED AT 250 WORDS)
