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Birefringence signals from surface and t‐system membranes of frog single muscle fibres.
Author(s) -
Baylor S M,
Oetliker H
Publication year - 1977
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1977.sp011663
Subject(s) - birefringence , polarity (international relations) , tonicity , depolarization , membrane , chemistry , biophysics , signal (programming language) , membrane potential , materials science , optics , physics , biology , biochemistry , computer science , cell , programming language
1. When the tonicity of Ringer is increased above 2‐5 times normal and a single fibre stimulated externally, the large, early birefringence signal preceding twitch tension (Baylor & Oetliker, 1975, 1977 a,b) is sufficiently reduced and delayed so as to reveal a small but distinct signal ('1st component") preceding it. For an average‐sized fibre, the deltaI/I of the 1st component was (minus) 1 to 2 x 10‐5. 2. The time course of the 1st component superimposed with the surface action potential simultaneously recorded by an internal micro‐electrode. The polarity of the 1st component reversed with compensation. 3. From these characteristics, the 1st component is thought to arise from a small change in optical retardation of the surface membrane due to the action potential. 4. When a fibre was impaled with two micro‐electrodes, retardation changes accompanying small hyperpolarizing and depolarizing current steps were detected. In some cases the polarity of the observed signal was opposite in sign to that expected for a retardation change only from the surface membrane. 5. Because the anatomical orientation of the T‐system appears to be primarily transverse rather than longitudinal, these signals of opposite polarity are probably, on balance, due to retardation changes from the membranes of the T‐system. 6. The possible origin of the large birefringence signal preceding contraction is discussed.