Spectrophotometric determination of reaction stoichiometry and equilibrium constants of metallochromic indicators: III. Antipyrylazo III complexing with Ca2+ and acetylcholine receptor protein

Stoichiometries, equilibrium constants and optical extinction coefficients of calcium-antipyrylazo III (An) complexing are determined with the analytical method described in article I of this series. Spcctrophotometric Ca titrations of An at the wavelengths 595 and 710 nm indicate overall dissociation equilibrium constants for the complexes CaAn, CaAn₂ and Ca₂An to be 4.5 × 10^?4 M, 1.1 × 10^?8 M² and 1.5× 10^?6 M², respectively, extrapolated to zero ionic strength. Ca titrations of solutions containing An plus acetylcholine receptor protein give clear evidence that An binds to the protein to a large extent in the presence of Ca²⁺; furthermore, addition of acetylcholine results in release of protein-bound Ca and An. This is the first reported indication that antipyrylazo III binds to biological material and questions the usefulness of this dye as a Ca indicator in biological systems.     

Oscillations in a collapsed-tube analog of the brachial artery under a sphygmomanometer cuff

To determine whether self-excited oscillations in a Starling resistor are relevant to physiological situations, a collapsible tube conveying an aqueous flow was externally pressurized along only a central segment of its unsupported length. This was achieved by passing the tube through a shorter and wider collapsible sleeve which was mounted in Starling resistor fashion in a pressure chamber. The tube size and material, and all other experimental parameters, were as used in our previous Starling resistor studies. Both low- and high-frequency self-excited oscillations were observed, but the low-frequency oscillations were sensitive to the sleeve type and length relative to unsupported distance. Pressure-flow characteristics showed multiple oscillatory modes, which differed quantitatively from those observed in comparable Starling resistors. Slow variation of driving pressure gave differing behavior according to whether the pressure was rising or falling, in accord with the hysteresis noted on the characteristics and in the tube law. The results are discussed in terms of the various possible mechanisms of collapsible tube instability, and reasons are presented for the absence of the low-frequency mode under most physiological circumstances.     

Enzymatic and chemical oxidation of gangliosides in cultured cells: effects of choleragen.

Cell surface glycolipids of normal human fibroblasts and NCTC2071 cells (transformed mouse fibroblasts) were labeled by incubating the intact cells with either galactose oxidase or sodium periodate, followed by reduction of the oxidized sugar residues with NaB3H4. In intact human fibroblasts, incorporation of 3H was increased with increasing time of exposure to galactose oxidase prior to treatment with NaB3H4. Following limited exposure to galactose oxidase, more label was incorporated into the larger glycolipids. Although labeling of the monosialoganglioside GM1 was maximal by 16 h, not all of the GM1 in the intact cells appeared to be accessible to galactose oxidase, since 10 to 12 times more GM1 was labeled when cells were disrupted before incubation with the enzyme. The human fibroblasts contained approximately 8 X 10(6) molecules of GM1 per cell. Maximal binding of choleragen (5 X 10(5) molecules of [125I]choleragen per cell) completely prevented cholevented oxidation of GM1 in intact fibroblasts by galactose oxidase but only partially protected the sialic acid moiety of GM1 from oxidation by periodate. Choleragen had little effect on the enzymatic or chemical oxidation of other glycolipids. NCTC 2071 cells do not contain endogenous GM1 but incorporate exogenous GM1 from the culture medium. When bound to NCTC 2071 cells, exogenous GM1 was protected by choleragen from oxidation by galactose oxidase or whether endogenous or taken up from the incubation medium, are, after interaction with choleragen, less accessible to oxidation by periodate or galactose oxidase.     

Glycosylation of human trophoblast integrins is stage and cell-type specific

Cytotrophoblasts are the specialized epithelial cells of theplacenta. During the first trimester, a subpopulation of chorionicvillas cytotrophoblasts differentiates along an invasive pathwayand penetrates the maternal endo-metrium, decidua and spiralarterioles. Cytotrophoblast invasiveness declines rapidly duringthe second half of gestation. Isolated cytotrophoblasts of differentgestational ages retain this differential invasiveness in culture.To determine whether the properties of integrin receptors forextracellular matrix molecules differ between invasive and non-invasivecytotrophoblasts, detergent extracts of isolated cytotrophoblastsof different gestational ages, and of first-trimester villousfibroblasts, were immunoprecipitated with subunit-specific anti-     

Evolution of insecticide resistance in Culex pipiens populations: The Corsican paradox

Culex pipiens mosquitoes from Corsica have been subject to insecticide treatments since 1971, using temephos (an organophosphate). After 17 years, resistance has not developed beyond a 14-fold level. This relatively low resistance is due to the presence of several identified resistance genes, including the insensitive target ( Ace^R ) and overproduced esterases (A1, A4 and B4). The fact that only a low resistance has developed after 17 years of treatment and that this low resistance level is the result of a relatively large number of resistance genes constitute a paradox. To understand this situation and explain why a higher temephos resistance level has not evolved in Corsica as in other parts of the world, it is proposed that the occurrence (through mutation or migration) of efficient resistance genes was a limiting step, and that the only resistance genes available at that time through migration from the surrounding Mediterranean countries had a low cross-resistance to temephos. The local situation of Corsica is discussed in the light of recent data on the world distribution of the known organophosphate resistance genes in this species, and the relative role of mutation and migration in the evolution of insecticide resistance in natural populations.