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C‐protein limits shortening velocity of rabbit skeletal muscle fibres at low levels of Ca2+ activation.
Author(s) -
Hofmann P A,
Greaser M L,
Moss R L
Publication year - 1991
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.1991.sp018689
Subject(s) - sarcomere , chemistry , extraction (chemistry) , skeletal muscle , chromatography , biophysics , endogeny , sodium , analytical chemistry (journal) , anatomy , biochemistry , myocyte , endocrinology , biology , organic chemistry
1. Effects on maximum shortening velocity (Vmax) due to partial extraction of C‐protein were investigated in skinned fibres from rabbit psoas muscles. Up to 80% of endogenous C‐protein was extracted, as assessed by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) of fibre segments obtained before and after the extraction protocol. Vmax was obtained at 15 degrees C by measuring the times required to take up various amounts of slack imposed at one end of the fibre. 2. During maximal activation with Ca2+, Vmax in control fibres was 4.26 +/‐ 0.16 (mean +/‐ S.E.M., n = 7) muscle lengths per second (ML/s). Following extraction of approximately 40% of endogenous C‐protein, Vmax in these same fibres was 4.41 +/‐ 0.24 ML/s. 3. At sufficiently low levels of submaximal activation, high‐ and low‐velocity phases of unloaded shortening were observed. Partial extraction of C‐protein significantly increased Vmax in the low‐velocity phase but had no effect on the high‐velocity phase. The effect on low‐velocity Vmax was fully reversed by re‐addition of purified C‐protein. 4. At low levels of activation, the amount of shortening to the break‐point between the high‐ and low‐velocity phases was not significantly affected by C‐protein extraction. Under control conditions the average break‐point was 85.6 +/‐ 3.1 nm/half‐sarcomere, while 84.1 +/‐ 3.1 nm/half‐sarcomere was obtained following partial extraction of C‐protein. 5. These results are considered in terms of a model in which an internal load slows Vmax at low levels of activation once a given amount of active shortening has occurred. C‐protein may contribute to this internal load either by binding to actin and myosin or by influencing mechanical properties of myosin cross‐bridges.