The Journal of General Physiology, Vol 76, Issue 6 729-750, Copyright © 1980 by Society of General Physiologists
Action potentials of isolated single muscle fibers recorded by potential-sensitive dyes
S. Nakajima and A. Gilai
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
Light transmission changes upon massive stimulation of single muscle fibers
of Xenopus were studied with the potential-sensitive nonpermeant dyes,
merocyanine rhodanine (WW375) and merocyanine oxazolone (NK2367). Upon
stimulation an absorption change (wave a) occurred, which probably
represents the sum of action potentials in the transverse tubules and
surface membrane. In WW375-stained fibers wave a is a decrease in
transmission over the range of 630 to 730 nm (with NK2367, over the range
of 590 to 700 nm) but becomes an increase outside this range, thus showing
a triphasic spectral pattern. This spectrum differs from that of the squid
axon, in which depolarization produces only an increase in transmission
over the whole range of wavelengths (Ross et al. 1977. J. Membr. Biol.
33:141-183). When wave a was measured at the edge of the fiber to obtain
more signal from the surface membrane, the spectrum did not seem to differ
markedly from that obtained from the entire width of the fiber. Thus, the
difference in the spectrum between the squid axon and the vertebrate muscle
cannot be attributed to the presence of the tubular system.
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