1. The effect of added inorganic phosphate (P i , range 3-25 mM) on active tension was examined at a range of temperatures (5-30°C) in chemically skinned (0.5 % Brij) rabbit psoas muscle fibres. Three types of experiments were carried out.2. In one type of experiment, a muscle fibre was maximally activated at low temperature (5°C) and its tension change was recorded during stepwise heating to high temperature in ~60 s. As found in previous studies, the tension increased with temperature and the normalised tension-(reciprocal) temperature relation was sigmoidal, with a half-maximal tension at 8°C.In the presence of 25 mM added P i , the temperature for half-maximal tension of the normalised curve was ~5°C higher than in the control. The difference in the slope was small.3. In a second type of experiment, the tension increment during a large temperature jump (from 5 to 30°C) was examined during an active contraction. The relative increase of active tension on heating was significantly higher in the presence of 25 mM added P i (30/5°C tension ratio of 6-7) than in the control with no added P i (tension ratio of ~3). In a third type of experiment, the effect on the maximal Ca 2+-activated tension of different levels of added P i (3-25 mM) (and P i mop adequate to reduce contaminating P i to micromolar levels) was examined at 5, 10, 20 and 30°C. The tension was depressed with increased [P i ] in a concentration-dependent manner at all temperatures, and the data could be fitted with a hyperbolic relation. The calculated maximal tension depression in excess [P i ] was ~65 % of the control at 5-10°C, in contrast to a maximal depression of 40 % at 20°C and 30 % at 30°C.5. These experiments indicate that the active tension depression induced by P i in psoas fibres is temperature sensitive, the depression becoming less marked at high temperatures. A reduced P i -induced tension depression is qualitatively predicted by a simplified actomyosin ATPase cycle where a pre-phosphate release, force-generation step is enhanced by temperature.

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The head portion of the myosin heavy chain (MHC) is essential in force generation. As previously shown, Ca2+-activated fibres of mammalian skeletal muscle display a strong correlation between their MHC isoform complement and the kinetics of stretch activation, suggesting isoform-specific differences in kinetic properties of myosin heads. Using the same methodology on muscle strips of atria and ventricles of hyper- and hypothyroid rats, this study showed that the kinetics of cardiac alphaMHC are 3 times faster than those of cardiac betaMHC under isometric conditions and maximal Ca2+ activation. Comparison of rat heart and skeletal muscle fibres revealed that 100% alphaMHC heart muscle strips exhibited faster stretch activation kinetics (time parameter t3: 108+/-18 ms, mean+/-SD) than rat type-IIA fibres ( t3: 157+/-19 ms), but slower than type-IID fibres ( t3: 55+/-10 ms). The kinetics of 100% betaMHC heart muscle strips ( t3: 351+/-44 ms) were faster than that of type-I fibres in rat skeletal muscle ( t3: 901+/-348 ms). This difference between the two muscle types calls in question the generally accepted identity of betaMHC and MHCIbeta.

Flexor digitorum profundus (FDP) tendon avulsions, although uncommon, are not infrequent injuries. A widely accepted method of treating Type 1 FDP avulsions is a pullout suture tied over a button on the nail plate. The external dorsal button is often a source of inconvenience for the patient. Potential risks associated with button use include nail plate deformities, nail fold necrosis and infections tracking along the sutures. The use of small suture anchors provides a satisfactory alternative, because buried fixation avoids these potential complications. This in vitro, biomechanical study examined the influence of the anchor orientation on the properties of the repaired FDP tendon using human cadavers.