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An asymmetry in the phosphate dependence of tension transients induced by length perturbation in mammalian (rabbit psoas) muscle fibres
Author(s) -
Ranatunga K. W.,
Coupland Moira E.,
Mutungi G.
Publication year - 2002
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.2002.019471
Subject(s) - tension (geology) , chemistry , amplitude , biophysics , contraction (grammar) , muscle contraction , analytical chemistry (journal) , anatomy , materials science , chromatography , physics , optics , compression (physics) , composite material , biology , endocrinology
The effects of inorganic phosphate (P i , a product released during ATP hydrolysis in active muscle) on tension transients induced by length perturbation (∼0.3 ms) were examined in chemically skinned (0.5 % Brij), maximally Ca 2+ ‐activated rabbit psoas muscle fibres at 10 °C (ionic strength 200 m m , pH 7.1). In one type of experiment, the tension transients induced by length release and stretch of a standard amplitude (0.4‐0.5 % of L o , muscle fibre length) were examined at a range of added [P i ] (range 3–25 m m ). The steady active tension was depressed ∼45 % with 25 m m added P i . The initial tension recovery (from T 1 , extreme tension reached after length step, to T 2 , tension after quick recovery) was analysed by half‐time measurement and also by exponential curve fitting ‐ extracting a fast (phase 2a) and a slow (phase 2b) component. The tension decay after a stretch became faster with increased [P i ], whereas the quick tension rise induced by a length release was insensitive to added P i . Consequently, the asymmetry in the speed of tension recovery from stretch and release was reduced at high [P i ]. A plot of the phase 2b rate (or 1/half‐time) of tension decay after stretch versus [P i ] was approximately hyperbolic and showed saturation at higher [P i ] levels. In a second type of experiment, the tension transients induced by length steps of different amplitudes were examined in control (no added P i ) and in the presence of 25 m m added P i . Over a range of length step amplitudes (up to 1 % L 0 ), the tension decay after stretch was consistently faster in the presence of P i than in the control; this was particularly pronounced in phase 2b. The rate of tension rise after length release remained high but similar in the presence and absence of added P i . These observations indicate that a stretch and release perturb different molecular steps in the crossbridge cycle. The P i sensitivity of tension decay (phase 2b) after stretch is similar to that seen using other perturbations (e.g. [P i ] jumps, hydrostatic pressure jumps and temperature jumps and sinusoidal length oscillations). The results indicate that the P i ‐sensitive force generation identified in previous studies is strain sensitive (as expected), but it is seen only with respect to positive strain (stretches).