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Effects of intracellular ruthenium red on excitation‐contraction coupling in intact frog skeletal muscle fibres.
Author(s) -
Baylor S M,
Hollingworth S,
Marshall M W
Publication year - 1989
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.1989.sp017480
Subject(s) - ruthenium red , biophysics , chemistry , endoplasmic reticulum , contraction (grammar) , skeletal muscle , stimulation , muscle contraction , coupling (piping) , anatomy , medicine , endocrinology , calcium , biochemistry , biology , materials science , organic chemistry , metallurgy
1. Ruthenium Red (RR) blocks sarcoplasmic reticulum (SR) Ca2+ release in disrupted muscle preparations and this block has been used as a marker for the physiological Ca2+ release pathway. To investigate whether RR can also affect SR Ca2+ release in living muscle, optical signals reflecting Ca2+ release have been measured in intact single frog twitch fibres microinjected with RR. 2. The total myoplasmic concentration of RR, [RRT], was obtained from measurements of RR‐related absorbance and apparent diffusion constant, Dapp, of RR in myoplasm was estimated. The value of Dapp was about 1/30 of that expected and can be explained if the majority of RR (approximately 97%) was bound in myoplasm and free [RR] was only 1/30 of [RRT]. 3. Sarcoplasmic reticulum Ca2+ release following action potential stimulation was assessed from a Ca2+‐related change in intrinsic birefringence. The birefringence signal was blocked in the presence of RR and the degree of block was clearly dependent upon [RRT]. At 16 degrees C the estimated [RRT] for half‐block of the birefringence signal was 23 +/‐ 4 microM (+/‐ S.E. of mean; n = 3), and for half‐block of the Ca2+ release process itself was 72 +/‐ 14 microM. The estimated free [RR] for half‐block is then 0.8 +/‐ 0.1 and 2.4 +/‐ 0.5 microM, respectively. In the cold (6‐8 degrees C), the half‐blocking concentration of RR, referred to [RRT], appeared to be about 3‐fold smaller than that observed at 16 degrees C. 4. The values estimated for the free [RR] which caused half‐block of Ca2+ release in intact muscle fibres are in the range reported for RR's action in disrupted preparations, thus supporting the conclusion that the RR‐blockable channel observed in disrupted muscle is the physiologically important Ca2+ release channel. 5. Intramembrane charge movements in skeletal muscle are thought to underlie the dependence of SR Ca2+ release on transverse tubular membrane potential. Charge movements were measured in RR‐injected fibres at 4‐6 degrees C using a three‐microelectrode, middle‐of‐the‐fibre voltage‐clamp technique. Injected fibres did not survive well in solutions made hypertonic to prevent fibre movement and allow measurement of suprathreshold charge; therefore charge movements below contraction threshold were studied in isotonic solution.(ABSTRACT TRUNCATED AT 400 WORDS)