Dissociation between mechanical performance and the cost of isometric tension maintenance in Lethocerus flight muscle.
A method for the continuous measurement of ATP hydrolysis (ATPase) by demembranated muscle fibres has been applied to isometrically held, glycerol-extracted flight muscle fibres from the water-bug Lethocerus, under conditions of high MgATP, neutral pH, and varying ionic strength, Ca2+ and extension. These variables caused parallel changes in isometric tension and ATPase. The slope of ATPase upon tension (delta ATPase/delta Tension; incremental tension cost) remained the same upon extension at either different Ca2+ concentrations or different ionic strength. Isometric activation by Ca2+ gave a higher incremental tension cost. The calculated mechanical rate constant of the work-producing process, measured by the small-amplitude behaviour, was increased by either Ca2+ or ionic strength, and little changed by extension; there was therefore a dissociation between its value and that of the incremental tension cost. The results appear to exclude a two-state crossbridge model for fibrillar insect flight muscle.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D005426:Flight, Animal; D007313:Insecta / Q000378:metabolism* / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000378:metabolism; D012026:Reflex, Stretch
D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D002118:Calcium