D A Martyn

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Force (F) and stiffness (K) were measured in glycerinated psoas fibers at various calcium levels with 0, 10, 20, and 30 mM orthophosphate (Pi) added to the bathing solutions. The concentrations of bathing solution constituents were as follows: 110 mM potassium, 40 mM sodium, 4 mM MgATP, 10 mM total EGTA, and variable amounts of MOPS (pH buffer). The pH was(More)
Calcium ions activate muscle contraction. The mechanism depends on the calcium sensitivity of the proteins that regulate contraction. Evidence is presented for the reverse phenomenon, where contraction modulates calcium sensitivity. Increasing the force level increased calcium sensitivity in intact fibers showing that the relation between force and calcium(More)
We explored the possibility that glucocorticoid-induced muscle weakness and atrophy resulted from impaired muscle membrane excitability. Male Sprague-Dawley rats received intramuscular injections of dexamethasone, cortisone acetate (equivalent anti-inflammatory doses), or saline for up to 28 days. Temporal patterns of change in muscle mass, twitch and(More)
The length and time dependence of shortening velocity (VL) at a very light load (1 mN) was determined for central segments of ferret papillary muscle at 27 degrees C. A recently developed technique that measures the cross-sectional area of the chosen segment was used to assess segment length. Segment length (SL) or force could be used as a feedback control(More)
Using a new technique that measures the length of a segment in the central region of isolated papillaries, we have determined the force-segment length relation for ferret papillary muscles at 27 degrees C. The muscles contracted under muscle length isometric (auxotonic) and segment isometric conditions in physiological solutions containing 9.0, 4.5, 2.25,(More)
This paper summarizes three lines of experimental evidence showing that crossbridge interaction affects calcium sensitivity and probably also affects calcium binding. Evidence is presented that this is a true hysteresis, not just a slow approach to equilibrium. In barnacle single muscle fibers injected with aequorin to monitor intracellular Ca, a long(More)
The segment length (SL) dependence of force (F) and light load shortening velocity (VL) was determined for central segments of ferret papillary muscles at different extracellular calcium concentrations. Muscles were maintained at 27 degrees C in a physiological solution which contained in mM: NaCl 140; KCl 5.0; MgSO4 1.0; NaH2PO4 1.0; acetate 20; the pH was(More)
The onset of relaxation has been studied in undamaged central segments of isolated ferret papillary muscles at 27 degrees C, 12 beats/min. A technique that provides a signal proportional to the length of a chosen segment was used to assess segment velocity and length. Feedback control was employed to obtain segment isometric contractions. At a variety of(More)
The effects of acute ethanol injection on force production were measured in normal and chronic alcoholic rats. Acutely injected normal rats, acutely injected chronic alcoholic rats, and noninjected chronic alcoholic rats were compared with control groups: normal nonalcoholic rats and a dietetically deprived control group. Acute ethanol injection increased(More)
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