An Na+-stimulated Mg2+-transport system in human red blood cells

The initial rate of net Mg2+ efflux was measured in human red blood cells by atomic absorption. In fresh erythrocytes incubated in Na+,K+-Ringer's medium this rate was 7.3 +/- 2.8 mumol/l cells per h (mean +/- S.D. of 14 subjects) with an energy of activation of 13 200 cal/mol. Cells with total Mg2+ contents ([ Mg]i) ranging from 1.8 to 24 mmol/l cells were prepared by using a modified p-chloromercuribenzenesulphonate method. Mg2+ efflux was strongly stimulated by increases in [Mg]i and in external Na+ concentrations ([ Na]o). A kinetic analysis of Mg2+ efflux as a function of [Mg]i and [Na]o revealed the existence of two components: an Na+-stimulated Mg2+ efflux, which exhibited a Michaelian-like dependence of free internal Mg2+ content (apparent dissociation constant = 2.6 +/- 1.4 mmol/l cells; mean +/- S.D. of six subjects) and on external Na+ concentration (apparent dissociation constant = 20.5 +/- 1.9 mM; mean +/- S.D. of four subjects) and a variable maximal rate ranging from 35 to 370 mumol/l cells per h, and an Na+-independent Mg2+ efflux, which showed a linear dependence on internal Mg2+ content with a rate constant of (6.6 +/- 0.7) X 10(-3) h-1. Fluxes catalyzed by the Na+-stimulated Mg2+ carrier were partially dependent on the ATP content of the cells and completely inhibited by quinidine (IC50 = 50 microM) and by Mn2+ (IC50 = 0.5-1.0 mM).     

Bemerkenswerte Pflanzenfunde aus Bosnien und der Herzegowina

Zusammenfassung In der vorliegenden Arbeit wurden Pflanzenarten besprochen, die selten oder neu für das Gebiet Bosniens und der Herzegowina, und meist von allgemeinem pflanzengeographischem Interesse sind. Einige dieser Funde wurden auf Dolomit oder Serpentinunterlage festgestellt, von welchen auch einige neue Sippen beschrieben wurden.     

Effects of DNase production, plasmid size, and restriction barriers on transformation of Vibrio cholerae by electroporation and osmotic shock

Attempts to transform wild type strains of V. cholerae with plasmid DNA by traditional osmotic shock methods were not successful. A mutant of V. cholerae that was deficient in extracellular DNase was transformed with plasmid DNA by osmotic shock, demonstrating directly that extracellular DNase is a major barrier to transformation of V. cholerae. Transformation of wild type and DNase-negative strains of V. cholerae was accomplished by electroporation. Efficiency of transformation by electroporation increased with field strength, decreased with plasmid size, and was relatively insensitive to changes in the electrolyte composition of the buffer as long as isotonic sucrose was present. Host-controlled modification/restriction systems also affected transformation efficiency in V. cholerae.     

R plasmids in environmental Vibrio cholerae non-O1 strains

The occurrence of drug resistance and its plasmid-mediated transferability was investigated in 140 environmental strains of Vibrio cholerae non-O1 and 6 strains of Vibrio cholerae, both O1 and non-O1, of clinical origin. Of the 146 strains tested, 93% were resistant to at least one drug and 74% were resistant to two or more antibiotics. The O1 strains were susceptible to all antibiotics used. A total of 26 of 28 selected resistant wild strains carried R plasmids that were transferable by intraspecific and intergeneric matings. The most common transmissible R factor determined resistance to ampicillin, amoxicillin, and sulfanilamide (30%), followed by resistance to ampicillin and amoxicillin (13%) and resistance to ampicillin, amoxicillin, phosphomycin, and sulfanilamide (9%). Comparison of the three methods of plasmid analysis showed that the method of Birnboim and Doly (Nucleic Acids Res. 7:1513-1523, 1979) without EDTA and lysozyme was optimal for isolation of both large and small plasmids in environmental V. cholerae strains. Most strains harbored more than one plasmid, and the molecular sizes ranged from 1.1 to 74.8 megadaltons. The plasmids of high molecular size (around 74 megadaltons) were responsible for the resistance pattern transferred and were maintained with high stability in the hosts.     

Isolation of Thy-1 caps and analysis of their phospholipid composition in mouse T-lymphoma cells

In this study we have used a density perturbation method to isolate anti-Thy-1 antibody-induced Thy-1 caps from mouse T-lymphoma cells in the absence of detergents, and then compared the phospholipid composit on of these capped membranes with that of uncapped membranes. Initial phospholipid analysis by two-dimensional thin layer chromatography (2-D TLC) reveals a significant increase in the amount of ³²P-labeled phosphatidylcholine in the Thy-1 capped membrane. In contrast, no significant changes are observed in the labeling of phosphatidylserine, phosphatidylethanolamine, or the sphingomyelins. Therefore, it is suggested that phosphatidylcholine may be involved in the organization and/or regulation of Thy-1 antigen redistribution. The composition of phosphoinositide in uncapped and capped membranes was analysed separately using one-dimensional thin layer chromatography (1-D TLC) to resolve phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), and phosphatidylinositol 4, 5-bisphosphate (PIP₂) from all other phospholipids. This analysis reveals a significant reduction in levels of PIP and PIP₂, but not PI, in Thy-1 caps. Through the use of ion exchange column chromatography, we have found an increased production of all three species of inositol phosphates during anti-Thy-1 antibody-induced capping. Inositol 1, 4, 5 -triphosphate (IP₃) shows the most significant increase, compared to the much smaller increases in inositol 4, 5-bisphosphate (IP₂) and inositol monophosphate (IP). These results suggest that the binding of anti-Thy-1 antibody to Thy-1 antigen activates phospholipase C which, in turn, initiates polyphosphoinositide turnover and IP₃ production. It is proposed that these observed effects are the result of early signal transducing events which are prerequisite steps in Thy-1 receptor cap formation.     

Gastric mucosal binding studies with enprostil: A potent anti-ulcer prostaglandin

The potent antiulcer prostaglandin enprostil binds with high affinity to porcine gastic mucosal tissues. This binding is saturable, dissociable and displaceable by compounds with similar structures. Various characteristics of binding such as pH optimum and displacement potencies suggest that enprostil binds to mucosal PGE₂ sites. Structure-activity and gastric mucosal binding relationships were also examined.     

Mammalian lignans: possible involvement in endogenous digitalis activity

Lignans are natural products, some of which were recently discovered in animal urines, semen and blood plasma. We investigated the actions of animal lignans obtained by total synthesis or extracted from urines of pregnant women on Na+, K+-ATPase in human red cells and human and guinea-pig heart cell membranes. Some of the tested lignans (enterolactone, prestegane B and 3-O-methyl enterolactone) inhibited Na+, K+-pump activity in human red cells with IC50 ranging from 5 to 9 X 10(-4) M. The IC50 for ouabain (7 X 10(-7) M) was not modified by addition of lignans. Enterolactone inhibited Na+, K+-ATPase activity in human and guinea pig heart membranes. It also displaced [3H]-ouabain binding from human heart with IC50 = 1.5 X 10(-4) M. The apparent dissociation rate constants (kd) of [3H]-ouabain were not different in presence of digoxin or enterolactone. Enterolactone exhibited a poor cross reactivity against antidigoxin antibodies. The aglycones of the lignans studied here were slight inhibitors of the Na+, K+-ATPase. However, we cannot exclude that a glycosyl- (and/or butenolide-) derivative of enterolactone could be one "endogenous ouabain-like" factor.     

Effects of Tween 80 and Freon 113 on Measles Virus

Measles vaccines were prepared from the same virus fluids by inactivation with formaldehyde or by extraction with ether, ethyl acetate, or Freon 113 in the presence of Tween 80. Tests of antigenic potency, based on antibody levels in guinea pigs, showed that the formaldehyde-inactivated vaccines were more potent than the solvent-inactivated preparations and had the additional advantage of long shelf life. Residual Tween 80 in the solvent-extracted vaccines resulted in marked loss of immunogenic potency without significant loss of hemagglutinating activity. Neither extraction with organic solvents nor exhaustive dialysis efficiently removed Tween 80 from aqueous solutions.