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: Book Reviews

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: Summary Several formations within the lower part of the Dalradian Appin Group are characterised by calcareous and calc-silicate lithologies. Amphibole occurs in these metasedimentary units in a variety of habits, from fine-grained disseminated crystals, through radiating aggregates permeating the whole rock, to dark green layers consisting of over 90% amphibole. Electron microprobe analyses of these amphiboles exhibit simple compositional trends from tremolite, through tremolitic hornblende to magnesio-hornblende. The only significant substitutions are from tremolite towards alumino-tschermakite [MgSi ⇌ AlviAliv] and from tremolite towards ferri-tschermakite [MgSi ⇌ FeviAliv]. This is in marked contrast to amphiboles from nearby suites of metavolcanic rocks and intrusive metadolerites which exhibit four coupled substitutions, leading from tremolite towards the ferro-actinolite, edenite, alumino-tschermakite and ferritschermakite end-members. These distinctive compositional trends may aid the distinction between para- and ortho-amphibolites elsewhere. Tremolitic amphibole commonly constitutes a high proportion of the calc-silicate rocks, the only other phases present being quartz ± phlogopite. Carbonate minerals are notably absent. This suggests that the sedimentary protolith was high in Mg, such as a dolomitic marl, possibly containing some magnesite. Sedimentological considerations suggest deposition in tropical latitudes in restricted coastal lagoons forming part of an extensive stable shelf bordering a mature landscape.

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 Single fibres of different sarcomere length at rest have been isolated from the claw muscle of the yabby (Cherax destructor), a decapod crustacean. Fibres of either long (SL 〉 6 μm) or short (SL 〈 4 μm) sarcomere length have been mechanically skinned and were maximally activated by Ca2+ and Sr2+ under various experimental conditions (ionic strength, in the presence of 2,3 butanedione monoxime (BDM)) to determine differences in their contractile properties. Isometric force was measured simultaneously with either myofibrillar MgATPase or fibre stiffness in both fibre types. The ultrastructure of individual long- and short-sarcomere fibres was also determined by electron microscopy. The long-sarcomere fibres developed greater tension (30.48±1.72 N cm−2) when maximally activated by Ca2+ compared with the short-sarcomere fibres (18.60±0.80 N cm−2). The difference in the maximum Ca2+-activated force can be explained by the difference in the amount of filament overlap between the two fibre types. The maximum Ca2+-activated myofibrillar MgATPase rate in the short-sarcomere fibres (1.60±0.27 mmol ATP l−1 s−1) was higher, but not significantly different from the ATPase rate in fibres with long-sarcomeres (1.09±0.14 mmol ATP l−1 s−1). As the concentration of myosin is estimated to be higher only by a factor of 1.22 in the short-sarcomere preparations there is no evidence to suggest that the myofibrillar MgATPase activity is different in the long- and short-sarcomere preparations. The maximum Ca2+-activated force (P 0) of both short- and long-sarcomere fibres was quite insensitive to BDM compared with vertebrate muscle. Force decreased to 60.2±5.3% and 76.1±2.7% in the short- and long-sarcomere fibres respectively in the presence of 100 mmol l−1 BDM. The difference in the force depression between the. long- and short-sarcomere fibres is statistically significant (p〈0.05). Fibre stiffness during maximum Ca2+-activation expressed as percentage maximum force per nm per half sarcomere was higher by a factor of 3.5 in short-sarcomere fibres than in long-sarcomere fibres suggesting that the compliance of the filaments in the long-sarcomere fibres is considerably higher than in the short-sarcomere fibres. Sr2+ could not activate the contractile apparatus to the same level as that seen by Ca2+ in either fibre type: the maximum Sr2+-activated force was (20±3%) and (63±3%) of the maximum Ca2+-activated force response in short- and long-sarcomere fibres, respectively. The ratio between fibre stiffness in the maximum Sr2+-activating solution and the Ca2+-activating solution was very similar to the ratio between the maximum Sr2+-activated force and Ca2+-activated force in either type of fibres, suggesting that the number of attached crossbridges is lower in the fibres when maximally activated by Sr2+ than when maximally activated by Ca2+. The short-sarcomere fibres were also more sensitive to changes in ionic strength than long-sarcomere fibres. In conclusion these results indicate that while several important specific characteristics of the short- and long-sarcomere length fibres (ATPase, maximum Ca2+-activated force and fibre stiffness) can be explained solely on differences in the ultrastructure (length and density per cross-sectional area of myosin filaments) there are also differences in the properties of the proteins involved in the force production and regulation evidenced by the differential effect of Sr2+, BDM and ionic strength on contractile activation in the two fibre types.