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Influence of ionic strength on the time course of force development and phosphate release by dogfish muscle fibres
Author(s) -
West Timothy G.,
Ferenczi Michael A.,
Woledge Roger C.,
Curtin N. A.
Publication year - 2005
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.2005.087106
Subject(s) - ionic strength , course (navigation) , phosphate , chemistry , biophysics , ionic bonding , anatomy , fishery , materials science , ion , biology , biochemistry , aqueous solution , engineering , aerospace engineering , organic chemistry
We measured the effects of ionic strength (IS), 200 (standard) and 400 mmol l −1 (high), on force and ATP hydrolysis during isometric contractions of permeabilized white fibres from dogfish myotomal muscle at their physiological temperature, 12°C. One goal was to test the validity of our kinetic scheme that accounts for energy release, work production and ATP hydrolysis. Fibres were activated by flash photolysis of the P 3 ‐1‐(2 nitrophenyl) ethyl ester of ATP (NPE‐caged ATP), and time‐resolved phosphate (P i ) release was detected with the fluorescent protein MDCC‐PBP, N ‐(2[1‐maleimidyl]ethyl)‐7‐diethylamino‐coumarin‐3‐carboxamide phosphate binding protein. High IS slowed the transition from rest to contraction, but as the fibres approached the isometric force plateau they showed little IS sensitivity. By 0.5 s of contraction, the force and the rate of P i release at standard and high IS values were not significantly different. A five‐step reaction mechanism was used to account for the observed time courses of force and P i release in all conditions explored here. Only the rate constants for reactions of ATP, ADP and P i with the contractile proteins varied with IS, thus suggesting that the actin–myosin interactions are largely non‐ionic. Our reaction scheme also fits previous results for intact fibres.