On the lack of inotropy of cardiac glycosides on skeletal muscle: a comparison of Na+, K+-ATPases from skeletal and cardiac muscle.

Comparison of Na,K-ATPase from skeletal and cardiac muscle revealed that, although the skeletal muscle enzyme was only slightly less sensitive to inhibition by ouabain, the rates of [³H]ouabain binding to, and dissociation from, the skeletal enzyme were much faster than the corresponding rates for the cardiac enzyme. The skeletal muscle enzyme required higher concentrations of potassium to stabilize the ouabainenzyme complex and to stimulate the K⁺-phosphatase activity. The K⁺-phosphatase activity was only 8% of the Na,K-ATPase activity of the skeletal muscle enzyme, compared to 22% for the cardiac preparation. The glycoprotein subunit found in Na,K-ATPases from cardiac and many other tissues appeared to be absent in the enzyme from skeletal muscle. The differences in binding and dissociation rates for ouabain suggest that there may be significant differences in the structure of the digitalis receptor in the two enzymes. The I₅₀ for ouabain inhibition of the skeletal muscle Na,K-ATPase was, however, only slightly higher than for the cardiac enzyme, suggesting that the lack of an inotropic effect of cardiac glycosides on skeletal muscle could not be due to failure of the digitalis drugs to bind to and inhibit the membrane-linked sodium pump.     

Direct measurement of the yield stress of filamentous fermentation broths with the rotating vane technique

The existence of a yield stress in filamentous fermentation broths has important transport phenomena implications in the design and operation of bioreactors. In this study, the constant shear rate vane method was assessed for directly measuring the yield stress of filamentous Aspergillus niger fermentation broths, as well as model fluids (ketchup, yogurt, and pulp suspensions). The method involved rotating 4-, 6-, and 8-bladed vanes (7.2 cm 相似文献   

Pharmacokinetics of stealth versus conventional liposomes: effect of dose

Liposomes which substantially avoid uptake into the mononuclear phagocyte system (MPS), termed Stealth liposomes, have recently been formulated (Allen, T.M. and Chonn, A., (1987) FEBS Lett. 223, 42-46). The pharmacokinetics of stealth liposomes as a function of liposome dose and a comparison to conventional liposome pharmacokinetics, was the subject of the present study. We have examined the tissue distribution of two different formulations of stealth liposomes, i.e., sphingomyelin:egg phosphatidylcholine:cholesterol:monosialoganglioside GM1 (SM:PC:CHOL:GM1) 1:1:1:0.2 and SM:PC:CHOL:polyethylene glycol distearoylphosphatidylethanolamine (PEG(1990)-DSPE) 1:1:1:0.2, and compared them with the tissue distributions seen for a liposomal formulation which is avidly removed from circulation by the cells of the MP system (PC:CHOL, 2:1). Tissue distribution in mice was examined over a 100-fold concentration range (0.1 to 10 mumol phospholipid/mouse) and at several time points over a 48 h time period. Liposome size ranged from 92-123 nm in diameter for all compositions. Clearance from blood of PC:CHOL liposomes following intravenous administration showed a marked dose dependence (i.e., saturation-type or Michaelis-Menten kinetics), with MPS uptake decreasing and % of injected dose in blood increasing as dose increased, over the entire dosage range. Injection of stealth liposomes, on the other hand, resulted in % of injected doses of liposomes in MPS, blood and carcass which were dose-independent and log-linear (first order kinetics) over the entire dosage range. The doses of stealth liposomes containing PEG(1900)-DSPE required for MPS saturation was higher than 10 mumol phospholipid/mouse or 400 mumol/kg. The dosage-independence of the pharmacokinetics of stealth liposomes and their lack of MPS saturation within the therapeutic dose range are two more assets, in addition to the prolonged circulation half-lives, leading towards their eventual use as drug delivery systems in the clinic.     

Fanconi anemia: evidence for linkage heterogeneity on chromosome 20q

Fanconi anemia is a rare autosomal recessive disorder in which affected individuals are predisposed to acute myelogenous leukemia and other malignancies. We report the results of a genetic linkage study involving 34 families enrolled in the International Fanconi Anemia Registry. A significant lod score was obtained between D20S20, an anonymous DNA segment from chromosome 20q, and Fanconi anemia (Zmax 3.04, theta max = 0.12). However, six other anonymous DNA segments from chromosome 20q, including D20S19, which is highly polymorphic and tightly linked to D20S20, showed no or only weak evidence for linkage to Fanconi anemia. An admixture test revealed significant evidence for linkage heterogeneity (chi 2 = 6.10, P = 0.01) at the D20S19 locus. Lod scores suggestive of linkage between Fanconi anemia and this locus were obtained with two of the largest kindreds studied (lods = 2.6 and 2.1, at theta = 0.001). Thus, our data support the provisional assignment of a Fanconi anemia gene to chromosome 20q.     

A simulation of evasive mimicry in the wild

The hypothesis of evasive mimicry proposes that: (a) the conspicuous coloration of some animals has evolved to warn predators that they are good at avoiding capture; and (b) this conspicuous coloration is mimicked by other, less evasive species which thus gain protection from predation. We have tested these ideas with wild birds as the predators and red and yellow pastry 'baits' as the prey. We used a specially constructed bird table to make one of the colours good at 'escaping': when a bird was about to eat a bait the observer pulled a cord which activated a mechanism that made the baits of one colour (but not the other) drop out of the bird's reach. We first measured the overall selection by the naive birds by presenting, for one day, a 'control' of equal numbers of non-evasive red and non-evasive yellow baits. The birds were then trained for 20 days on equal numbers of evasive yellow and non-evasive red baits, and were then again given a second control (in which the yellows were now non-evasive 'mimics'). The training was repeated for 18 days but with red as the evasive colour, and a third control was then presented (with reds now as the mimics). The proportions attacked daily in the two training sessions suggested that the birds were learning to ignore yellows in the first and reds in the second. In comparison with the first control, fewer yellows were eaten after they had been trained to ignore escaping yellows, and more were eaten after they had been trained on escaping reds. We conclude that the results are further evidence for the hypothesis of evasive mimicry.     

Basophils in skin reactions of mast cell-deficient mice infested with Dermacentor variabilis

Acquired resistance to ticks in guinea pigs has been found to be associated with basophil-rich skin reactions. Mice, which are generally believed to possess few, if any basophils, also acquire resistance following repeated tick infestations and this has been found to be associated with increased numbers of dermal mast cells. Mast cell-deficient W/Wv mice have, however, also been shown capable of acquiring resistance after two infestations with Dermacentor variabilis larvae. In the studies described here, we have examined, with the electron microscope, skin reactions in W/Wv and +/+ mice undergoing their third infestation with Dermacentor variabilis. Basophils, along with neutrophils and eosinophils, were identified using established criteria. The possibility that basophils contribute to various pathogenetic mechanisms in these and other strains of mice is discussed.     

Determination of 35S-aminoacyl-transfer ribonucleic acid specific radioactivity in small tissue samples

Rate determination of protein synthesis utilizing tracer amino acid incorporation requires accurate assessment of the specific radioactivity of the labeled precursor aminoacyl-tRNA pool. Previously published methods presumably useful for the measurement of any aminoacyl-tRNA were unsuccessful when applied to [³⁵S]methionine, due to the unique chemical properties of this amino acid. Herein we describe modifications of these methods necessary for the measurement of ³⁵S-aminoacyl-tRNA specific radioactivity from small tissue samples incubated in the presence of [³⁵S]methionine. The use of [³⁵S]methionine of high specific radioactivity enables analysis of the methionyl-tRNA from less than 100 mg of tissue. Conditions for optimal recovery of ³⁵S-labeled dansyl-amino acid derivatives are presented and possible applications of this method are discussed.     

Yeasts from Marine and Estuarine Waters with Different Levels of Pollution in the State of Rio de Janeiro, Brazil

Yeast counts were made at 24 marine and estuarine sites in the vicinity of Rio de Janeiro, Brazil. Mean salinities of estuarine sites ranged from 14.2 to 27.4‰, and mean temperatures ranged from 25 to 28°C. Total coliform counts varied from 80% above 100,000 colony-forming units (CFU)/100 ml at heavily polluted sites to 100% below 100 CFU/100 ml at unpolluted sites. Total yeast counts above 100 CFU/100 ml were typical of heavily and moderately polluted water but atypical of lightly polluted and unpolluted water. Mean total yeast counts were 2,880 CFU/100 ml for heavily polluted sites, 202 CFU/100 ml for moderately polluted sites, and 3 CFU/100 ml for lightly polluted and unpolluted sites. Total yeast counts had a positive response to increased pollution levels, and Candida krusei and phenotypically similar yeasts as a group were prevalent in polluted estuarine water but rare in unpolluted seawater. The 549 strains of yeasts and yeast-like organisms isolated were grouped into 67 species, of which the 21 most prevalent made up 86% of the total yeast population. The prevalent genera in the polluted estuary were Candida, Rhodotorula, Torulopsis, Hanseniaspora, Debaryomyces, and Trichosporon.