Sites of action of D2O in intact and skinned crayfish muscle fibers

Summary The effect on tension development of replacing 90% of the H₂O of the bathing saline with D₂O was studied on intact single fibers, and on skinned fibers before and after the latter were treated so as to eliminate Ca-accumulation by the sarcoplasmic reticulum (SR). Excitation-contraction coupling (ECC) of intact fibers is not abolished, but is depressed by D₂O so that higher depolarizations are required to elicit a given tension. The reduction in tension at a given level of depolarization is not due to inhibition of the contractile system. The latter showed an enhanced Ca sensitivity; that is, skinned fibers respond to Ca concentrations that are 1–2 orders of magnitude smaller in D₂O than in H₂O saline. When bathed in D₂O saline, intact fibers or skinned fibers with functional SR can still accumulate and release Ca in sufficient quantities to allow repeated induction of maximum tensions. Relaxation is slowed in all three types of preparation, perhaps because of an increased affinity of troponin to Ca in D₂O salines.     

The ultrastructure of the middle cerebral artery and its associated nerve fibers in the squirrel monkey and baboon

This study describes the ultrastructural characteristics of the middle cerebral artery and its related neural elements in the squirrel monkey and baboon. The cytoarchitecture of the M-1 segment as well as that of the smaller extracerebral and intracerebral vessels is comparable in both animals.Smooth muscle elements are occasionally found within the intimai lining. The nerve bundles associated with vessels contain fewer myelinated fibers as the vessel diameter decreases. The cytological relationship between the neural structures and the smooth muscle cells are discussed.     

Fluid excretion by adult Aedes aegypti mosquitoes

Only clear cloacal fluid was eliminated during the first 30–60 min after emergence of feeding on human blood. Neither meconium nor blood was voided. More liquid was excreted after withdrawing blood than after ecdysis, but the pattern of emission was the same, in that fluid was ejected rapidly only or mostly over the first 10–15 min after these events. Diuresis was not exhibited after adults fed on either sucrose or fructose. Injury prevents the release of the diuretic hormone.     

Composition,abundance, and diversity of peracarid crustaceans on a transect of the Kolbeinsey Ridge,north of Iceland

Composition, abundance, and diversity of Crustacea Peracarida were investigated on a transect across the Kolbeinsey Ridge, north of Iceland in summer 1992 during the M21/5 expedition with RV Meteor. This ridge is influenced by both the cold East Greenland Current as well as the warmer East Iceland Current, mixing with warmer Atlantic water. Sampling has been performed using an epibenthic sledge modified after Rothlishberg & Pearcy (1977). Being one of the most important components of the macrobenthic epi- and suprafauna, composition, abundance, and diversity of peracarids was significantly different on western and eastern sides of the slope. Isopoda and Amphipoda were most frequent at all stations, followed by Cumacea and Tanaidacea. Mysidacea have only been sampled on the eastern slope. Abundance and diversity were highest on the two eastern stations in depths of 830–940 meters, values decreased on the deepest eastern station in 1100 meter depth and were also low on both western stations in 830 and 860 meters depth. These differences are probably due to sediment composition and to quality and quantity of organic carbon reaching the seafloor, rather than to differences in salinity or in hydrographic regimes. The high abundance of peracarid crustaceans, especially of epibenthic species, capable of burrowing within the first centimeters of sediment, indicate their high potential of bioturbation and also their importance for benthic carbon cycling.     

Splicing of the Muscle-Specific Plasma Membrane Ca2+-ATPase Isoform PMCA1c Is Associated with Cell Fusion in C2 Myocytes

Abstract: The regulation of intracellular calcium is essential for proper muscle function. Muscle cells have several mechanisms for dealing with the rapid and large changes in cytosolic calcium level that occur during contraction. Among these is the plasma membrane Ca²⁺-ATPase (PMCA), which pumps calcium from the cytosol to the extracellular space. We have previously shown that in human fetal muscle the PMCA1 isoforms present are PMCA1a-d, with PMCA1b and c predominating. Alternative splicing of mRNAs encoding proteins involved in muscle contraction is common in developing muscle. Therefore, we examined the expression of muscle-specific PMCA mRNAs in pre- and postfusion mouse C2 myoblasts. The housekeeping form of the Ca²⁺-ATPase, PMCA1b, was found at all times and under all conditions. However, the other predominating isoform found in muscle, PMCA1c, was expressed on myotube formation. Simple cell-cell contact was not sufficient to induce PMCA1c expression, as cells plated at confluence but harvested before myotube formation did not express PMCA1c. The induction of this muscle-specific Ca²⁺-ATPase at myotube formation suggests that it may play an important role in muscle function.     

o,p'-DDD in the mouse lung: selective uptake, covalent binding and effect on drug metabolism

By means of autoradiography a high and selective accumulation was observed in the lung alveolar region of C57Bl mice injected with o,p'-[14C]DDD. Exhaustive extraction of lung tissue showed that a large fraction of the radioactivity was covalently bound to protein. Covalent binding in liver was 20-30 times lower and represented a smaller fraction of the total radioactivity present in this tissue. Formation of a cytochrome P-450 catalysed reactive metabolite in lung and liver was indicated by a decreased covalent binding in these tissues in mice pretreated with metyrapone. Both beta-naphthoflavone (beta NF) and phenobarbital (PB) pretreatment decreased binding of o,p'-DDD in lung tissue, while binding in the liver was induced by PB but remained unaffected by beta NF. Pretreatment with high doses of o,p'-DDD and p,p'-DDT gave a significantly decreased binding of o,p'-[14C]DDD in lung, whereas binding in liver remained unchanged. Conjugation with glutathione does not appear to be a major inactivation pathway for the reactive lung metabolite, since a high dose of o,p'-DDD did not deplete non-protein thiols (NPSH) in lung tissue. Pretreatment with o,p'-DDD decreased the N-demethylation of [dimethyl-14C]aminopyrine in both lung and liver in a dose-dependent manner, suggesting that the drug-metabolizing enzyme system may be a target for o,p'-DDD in vivo.