ALBERT

Notes: A finite-element method which incorporates mesh adaptation is used to calculate ground-water flow and pollutant transport. The formulation is based on the equations for conservation of mass, Darcy's law for an anisotropic medium, and the time-dependent species transport equation. Modifications have been implemented to the finite-element formulation to enhance computational speed and reduce storage; Petrov-Galerkin weighting of the advection terms provides numerical stability. An explicit time marching scheme is used to solve the transient equations. By utilizing unstructured adaptive meshing, species concentration and location of steep fronts are accurately resolved, even though one begins with a coarse mesh. The algorithm currently runs on PC and workstation class computers.

Notes: Abstract  The total ozone column is well correlated with tropospheric fields such as the heights of the upper tropospheric geopotential surfaces and thus it can provide useful information on temporal variability in the troposphere. The global availability of long period satellite measurements of the total ozone column, taken by the TOMS instruments since 1978, provides a valuable and independent data set for use in studies of seasonal and interannual climate variability. In this study, the global low-frequency seasonal teleconnections in the observed TOMS data from 1979–91 have been investigated using seasonal teleconnectivity maps and empirical orthogonal function analysis. They have also been compared with the results from a simulation made with the atmospheric GCM at Météo-France, having prescribed observed sea surface temperatures for the same period. In the observed total ozone, strong ENSO-related wave number one longitudinal dipole patterns are seen in both the tropics and in the Southern Hemisphere extratropics. The model shows much weaker variability in total ozone yet appears to be able to capture similar teleconnection patterns in the tropics related to ENSO. In the SH extratropics, the model total ozone shows a strong wave number 3 response rather than the wave number one dipole seen in the observations. A wave number 3 response is also evident in the 200 hPa geopotential height simulated by the model and in the NCEP analysis, and is consistent with the response in a linearised barotropic model forced in the Indonesian region. The different responses in the modelled and observed total ozone, suggest that tropopause effect is not the major factor in the SH extratropics, and it is likely that horizontal ozone transport also plays a role in this region. Despite a generally poor simulation of the zonal mean total ozone, the model was able to capture the anomalous strengthening of the SH stationary waves during austral spring of 1988, related to an intense stratosphere sudden warming.

Notes: Abstract The influence of supersolidus liquid phase sintering (SLPS) on the density of sintered components manufactured using a Ni-base superalloy powder (N18) has been studied. A compression moulding technique was employed to simulate the metal injection moulding (MIM) process using coarse N18 powder, with a particle size distribution of 40–63 μm, as opposed to fine powders of less than 10μm normally used in conventional MIM. The study has demonstrated how the problem of low sintered density, encountered in solid-state sintering using coarse powders, can been overcome by SLPS and that the sintered densities of the N18 powder via the moulding process route were comparable with those produced by conventional die pressing and sintering.

Notes: Summary To understand how the coexistence of fast and slow contractile and regulatory systems within single skeletal muscle fibres might affect contractile behaviour, fibre segments from the fast-twitch extensor digitorum longus and predominantly slow-twitch soleus muscle of the adult rat were tied together, either in parallel or in series, and then activated in Ca2+-and Sr2+-buffered solutions. Experimental force-pCa and force-pSr relations were compared with theoretical force-pCa and force_pSr curves predicted by a model for composite fibres, which accounted for the coexistence of fast and slow myosin within the contractile unit and enabled an estimate to be made of the relative contribution of fast- and slow-twitch elements within the tied-fibre combinations. The contractile behaviour of a fast-twitch and a slow-twitch muscle fibre tied either in series or in parallel, were compared with the force-pCa and force-pSr data predicted from the composite fibre model. Interestingly, the resultant force-pCa(-pSr) curves of the parallel-tied fibre combinations were well fitted with those predicted by the composite model. However, the experimental force-pCa(-pSr) curves of the series-tied fibres were not well fitted by a composite curve based on the known proportion of fast- and slow-twitch fibre components. A total force-length diagram was devised to take into account changes in the length of the fibre segments tied in series during activation, as well as possible differences in fibre diameter. Using this diagram it was possible to explain accurately the Ca2+ and Sr2+ activation curves of known fast- and slow-twitch segments tied in series. The results from this study are important for the interpretation of contractile date obtained from single muscle fibres exhibiting mixed fast- and slow-twitch contractile characteristics. Such muscle fibres have previously been identified in animals affected by muscular diseases (e.g. dystrophy), in mammalian extraocular muscles and in animals subjected to long-term exercise training.

Notes: Summary In this study, we investigated the effect of the Ca2+ pump inhibitor, 2,5-di-(tert-butyl)-1,4-hydroquinone on the function of the contractile apparatus, Ca2+ uptake, the permeability of the sarcoplasmic reticulum to Ca2+ and excitation-contraction coupling, in mechanically skinned muscle fibres of the rat and toad. 2,5-di-(tert-butyl)-1,4-hydroquinone had no significant effect on the maximum force and Ca2+ sensitivity of the contractile apparatus in rat and toad fibres at concentrations of 20 and 5 μM respectively. In rat fibres, 2,5-di-(tert-butyl)-1,4-hydroquinone was found to inhibit sarcoplasmic reticulum Ca2+ loading in a dose dependent manner, with a half maximal effect at 2 μM. In toad fibres, 5 μM 2,5-di-(tert-butyl)-1,4-hydroquinone completely blocked sarcoplasmic reticulum Ca2+ loading. Exposure to 5 mM BAPTA revealed a small resting sarcoplasmic reticulum Ca2+ leak in unstimulated rat fibres. This Ca2+ leak was not significantly affected by the presence of 20 μM 2,5-di-(tert-butyl)-1,4-hydroquinone, suggesting that 2,5-di-(tert-butyl)-1,4-hydroquinone does not substantially block or activate the sarcoplasmic reticulum Ca2+ release channels. Depolarisation-induced force responses elicited in rat and toad skinned fibres were not significantly affected by 0.5 μM 2,5-di-(tert-butyl)-1,4-hydroquinone. In the rat fibres, 5 and 20 μM 2,5-di-(tert-butyl)-1,4-hydroquinone greatly increased the peak and duration of initial depolarisation-induced force responses, while subsequent responses were reduced. 2,5-di-(tert-butyl)-1,4-hydroquinone did not affect excitation contraction coupling, as depolarisation-induced force responses similar to initial controls could be elicited after 2,5-di-(tert-butyl)-1,4-hydroquinone exposure, provided that the initial Ca2+ release in 2,5-di-(tert-butyl)-1,4-hydroquinone was chelated with 0.5 mM EGTA (to prevent Ca2+-dependent damage) and the sarcoplasmic reticulum was reloaded with Ca2+. In the toad fibres, 5 μM 2,5-di-(tert-butyl)-1,4-hydroquinone had a similar effect on depolarisation-induced force responses to that observed at 20 μM 2,5-di-(tert-butyl)-1,4-hydroquinone in rat fibres. This study shows that 2,5-di-(tert-butyl)-1,4-hydroquinone specifically and reversibly inhibits the sarcoplasmic reticulum Ca2+ pump in skeletal muscle and therefore, 2,5-di-(tert-butyl)-1,4-hydroquinone could be a valuable tool for investigating the role of the sarcoplasmic reticulum in Ca2+ homeostasis in skeletal muscle.

Notes: Summary Mechanically skinned fibre preparations from the extensor digitorum longus muscle of the rat were used to test whether a rise in myoplasmic [NH4 +] in the range 2–10 mm interferes with the mechanism of excitation-contraction coupling in fast-twitch mammalian muscle. Under our conditions (pH 7.10, Mg2+ 1 mm, temperature 23° C), [NH4 +] up to 10 mm had little effect on the Ca+-activated force and on the peak of the t-system depolarization-induced force response. However, the duration of the depolarization-induced force response was decreased significantly at [NH4 +] ≥2 mm. From these data we conclude that the intracellular accumulation of NH4 + is not likely to play a major role in fatigue. Nevertheless, the build up of NH4 + during fatigue, may have a significant inhibitory effect on the force output by decreasing the duration of the t-system depolarization-induced activation of the contractile apparatus.

Notes: Abstract The main objective of this study was to analyse glycogen in single muscle fibres, using a recently developed microfluorometric method which detects subpicomol amounts of NADPH, glucose and glycogen (as glucosyl units) (detection limit 0.16–0.17pmol in a 25nl sample) without fluorochrome amplification. The fibres were freshly dissected from the twitch region of the iliofibularis muscle of the cane toad (Bufo marinus), and were mechanically skinned under paraffin oil to gain access to the intracellular compartments. The results show that: (1) glycogen concentrations in toad skeletal muscle fibres range between 25.8 and 369mmol glucosyl units/litre fibre volume; (2) there is a large variation in glycogen content between individual fibres from the iliofibularis muscle of one animal; (3) there are seasonal differences in the glycogen content of toad single muscle fibres; (4) the total amount of glycogen in single muscle fibres of the toad does not decrease significantly when storing the tissue, under paraffin oil, at 20–25°C for up to 6h or at 4°C for up to 24h; and (5) 15–26% of fibre glycogen can be washed in an aqueous solution at pH 5–7, within 5min, while 74–85% of fibre glycogen remains associated with the washed skinned fibre, even after 40min exposure of the skinned fibre preparation to the aqueous environment. The retention of most glycogen in the fibre preparation after mechanical removal of the plasma membrane and extensive washing indicates that in toad skeletal muscle fibres the largest proportion of glycogen is tightly bound to intracellular structures. The results also show that the skinned muscle fibre preparation is well suited for microfluorometric glycogen determination, since low molecular weight non-glycogen contributors to the fluorescence signal can be removed from the myoplasmic space prior to the glycogen hydrolysis step.

Notes: Summary The effect of temperature (5–35° C) on maximum force production was examined in intact and chemically skinned muscle fibre bundles (10–25 fibres) from the anterior byssus retractor muscle of Mytilus edulis. In intact fibre bundles, 10 μm acetylcholine induced a tonic contraction which had a magnitude of 65.4±4.0 N cm-2 (n=30) at 23° C. Activation by caffeine (20 mm) produced a force response which was 157.1±7.9% (n=16) of the acetylcholine response at 23° C and acetylcholine and caffeine together produced force which was not significantly different from the response to caffeine alone. At 5° C the acetylcholine and caffeine responses were decreased by 9.6±3.4% (n=6) and 14.6±2.8% (n=8) compared with the respective responses at 23° C. However, there was no significant reduction of the response induced by the combined action of acetylcholine and caffeine when the temperature was decreased from 23° C to 5° C. The 20–80% of peak force activation time increased by about one order of magnitude for all acetylcholine, caffeine and combined acetylcholine-caffeine-induced responses when the temperature was decreased from 23–5° C. Repeated exposure of the intact preparation to caffeine caused a marked decrease in the caffeine-induced response (complete abolition of force after the third exposure to caffeine), but the response to caffeine could be fully restored following one acetylcholine-induced activation. The maximum Ca2+-activated force after skinning the preparation with saponin was not significantly different from the caffeine or combined acetylcholine-caffeine-induced responses before skinning. In the saponin skinned fibre preparation a drop in temperature from 23° C to 15° C or 5° C decreased the maximum Ca2+-activated force by 13.2±1.4% (n=8) and 41.4±3.1% (n=5) respectively. The activation time between 20–80% of the peak Ca2+-activated force increased at 15° C and 5° C by a factor of 1.5±0.1 (n=5) and 6.8±1.1 (n=5) respectively when compared to corresponding values at 23° C. The relaxation half-time decreased by a factor of 1.7±0.2 (n=5) and 3.0±0.2 (n=5) at 15° C and 5° C respectively compared with that at 23° C. It was possible to distinguish between the temperature effects on the contractile apparatus per se and the Ca2+ regulatory system with the results indicating that the contractile apparatus was more sensitive to a change in temperature than the Ca2+-regulatory system. Increasing the temperature to 35° C irreversibly affected the ability to develop and maintain force in both intact and skinned muscle preparations. These results indicate that: (1) acetylcholine does not fully activate the intact ‘catch’ muscle at 23° C; (2) acetylcholine is able to replenish the internal stores after depletion by caffeine; (3) compensatory mechanisms which oppose the inhibitory effect of lower temperatures on the contractile apparatus and the Ca2+-regulatory system must be operating in the intact fibre preparations.

Notes: Abstract The rate, magnitude and pharmacology of inorganic phosphate (Pi) transport into the sarcoplasmic reticulum were estimated in single, mechanically skinned skeletal muscle fibres of the rat. This was done, indirectly, by using a technique that measured the total Ca2+ content of the sarcoplasmic reticulum and by taking advantage of the 1:1 stoichiometry of Ca2+ and Pi transport into the sarcoplasmic reticulum lumen during Ca--Pi precipitation- induced Ca2+ loading. The apparent rate of Pi entry into the sarcoplasmic reticulum increased with increasing myoplasmic [Pi] in the 10 mm--50 mm range at a fixed, resting myoplasmic pCa of 7.15, as judged by the increase in the rate of Ca--Pi precipitation-induced sarcoplasmic reticulum Ca2+ uptake. At 20 mm myoplasmic [Pi] the rate of Pi entry was calculated to be at least 51 μm s−1 while the amount of Pi loaded appeared to saturate at around 3.5 mm (per fibre volume). These values are approximations due to the complex kinetics of formation of different species of Ca--Pi precipitate formed under physiological conditions. Phenylphosphonic acid (PhPA, 2.5 mm inhibited Pi transport by 37% at myoplasmic pCa 6.5 and also had a small, direct inhibitory effect on the sarcoplasmic reticulum Ca2+ pump (16%). In contrast, phosphonoformic acid (PFA, 1 mm) appeared to enhance both the degree of Pi entry and the activity of the sarcoplasmic reticulum Ca2+ pump, results that were attributed to transport of PFA into the sarcoplasmic reticulum lumen and its subsequent complexation with Ca2+. Thus, results from these studies indicate the presence of a Pi transporter in the sarcoplasmic reticulum membrane of mammalian skeletal muscle fibres that is (1) active at physiological concentrations of myoplasmic Pi and Ca2+ and (2) partially inhibited by PhPA. This Pi transporter represents a link between changes in myoplasmic [Pi] and subsequent changes in sarcoplasmic reticulum luminal [Pi]. It might therefore play a role in the delayed metabolic impairment of sarcoplasmic reticulum Ca2+ release seen during muscle fatigue, which should occur abruptly once the Ca--Pi solubility product is exceeded in the sarcoplasmic reticulum lumen