Coexistence of Probe Conformations in Lipid Phases—A Polarized Fluorescence Microspectroscopy Study

Several well-established fluorescence methods depend on environment-sensitive probes that report about molecular properties of their local environment. For reliable interpretation of experiments, careful characterization of probes’ behavior is required. In this study, bleaching-corrected polarized fluorescence microspectroscopy with nanometer spectral peak position resolution was applied to characterize conformations of two alkyl chain-labeled 7-nitro-2-1,3-benzoxadiazol-4-yl phospholipids in three model membranes, representing the three main lipid phases. The combination of polarized and spectral detection revealed two main probe conformations with their preferential fluorophore dipole orientations roughly parallel and perpendicular to membrane normal. Their peak positions were separated by 2–6 nm because of different local polarities and depended on lipid environment. The relative populations of conformations, estimated by a numerical model, indicated a specific sensitivity of the two probes to molecular packing with cholesterol. The coexistence of probe conformations could be further exploited to investigate membrane organization below microscopy spatial resolution, such as lipid rafts. With the addition of polarized excitation or detection to any environment-sensitive fluorescence imaging technique, the conformational analysis can be directly applied to explore local membrane complexity.     

Electroencephalographic changes in the lateral septum complex following systemic administration of DES-TYR1 -α-endorphin,Des-Tyr1-γ-endorphin and haloperidol in rats

The influence of systemically administered Des-Tyr¹-α-endorphin (DTαE), Des-Tyr¹-γ-endorphin (DTγE) and haloperidol on electroencephalographic (EEG) activity of the lateral septum complex (LSC) and the frontal cortex was studied in male rats. DTαE (2 μg) significantly increased whereas DTγE (10 μg) significantly decreased the amounts of activity in the 5 Hz band. In addition, DTαE promoted production of 15 - 20 Hz activity, while DTγE decreased the amount of 20 - 30 Hz activity. EEG activity exhibited a marked variability which persisted throughout the recording session following administration of the peptides. Haloperidol markedly decreased the proportion of 10 - 15 Hz activity. The alterations in EEG of the frontal cortex were similar to those in LSC but less pronounced. The differences in the time course and frequency bands affected suggest that the effects of peptides and haloperidol on EEG activity of LSC are not mediated by the same mechanisms.     

Genetic differentiation of Elysia timida (Risso, 1818) populations in the Southwest Mediterranean and Mar Menor coastal lagoon

Genetic variation at 10 enzyme loci was analysed in Elysia timida sacoglossan mollusc samples, originating from both coastal lagoon and marine sites. The observed heterozygosity ranged from 0.390 (Los Urrutias) to 0.277 (Tabarca). Marine and coastal lagoon populations were characterised by exclusive alleles.     

THE INTRACELLULAR MEMBRANES OF BLASTOMYCES DERMATITIDIS

Edwards , George A., and Mercedes R. Edwards . (Div. Labs, and Research, N.Y.S. Dept. of Health, Albany.) The intracellular membranes of Blastomyces dermatitidis. Amer. Jour. Bot. 47 (8): 622–632. Illus. 1960.—The yeast cells of Blastomyces dermatitidis have been studied in thin sections with the electron microscope. The cell is multinucleate, and the nuclei are frequently interconnected by their outer limiting membranes. The cell is bordered by a cell wall and the plasma membrane, which may be seen in direct continuity with the nuclear envelope. The cytoplasm contains numerous mitochondria, many profiles of the endoplasmic reticulum, and few multivesicular bodies. The membranes of all the constant cellular components are interconnected. Mitochondria appear to be formed from any of several membrane systems. The micromorphology of the cell suggests efficiency of communication and cytoplasmic mobility.     

Genetic interaction between Non-MHC T- and B-cell alloantigens in response to rous sarcomas in chickens

Chickens of Regional Poultry Research Laboratory (RPRL) inbred line 6₃ regress sarcomas induced by Bryan high-titer Rous sarcoma virus to a greater extent than chickens of line RPRL 100, although these lines are identical for the major histocompatibility B complex. They differ, however, at three independent autosomal loci: Ly-4 and Th-1 determine the surface alloantigens of partly overlapping subsets of T lymphocytes, and Bu-1 determines a surface alloantigen of B lymphocytes. The association of genotypes at these loci with quantitative variation in their ability to regress Rous sarcomas was tested in segregating F₄ generation progeny derived from crosses of lines 100 and 6₃. The Ly-4 and Bu-1 genotypes showed association with Rous sarcoma regression, but the Th-1 genotype did not. Chickens of the Ly-4 ^a/Ly-4 ^a, Bu-1 ^b/Bu-1 ^b and Ly-4 ^b/Ly-4 ^b, Bu-1 ^a/Bu-1 ^a genotypes had a significantly higher regressor ability than the other two double homozygous genotypes. These results indicate that higher regression is associated with (1) interaction between the Ly-4 and Bu-1 loci, and (2) complementation between either the line 6 Ly-4 ^a allele and the line 100 Bu-1 ^b allele, or the line 100 Ly-4 ^b allele and the line 6 Bu-1 ^a allele.     

Purified Fc epsilon R+ bone marrow and splenic non-B, non-T cells are highly enriched in the capacity to produce IL-4 in response to immobilized IgE, IgG2a, or ionomycin.

Non-B, non-T cells from spleen and bone marrow cells produce IL-4 in response to cross-linkage of high affinity receptors for Fc epsilon R or Fc gamma RII, and to treatment with calcium ionophores. Cells bearing high affinity Fc epsilon R constituted 1 to 2% of non-B, non-T cells of spleen and of total bone marrow cells from naive donors. In mice whose immune systems had been polyclonally activated by injection with anti-IgD antibodies or had been infected with Nippostrongylus brasiliensis larvae, the frequency of Fc epsilon R+ cells in splenic non-B, non-T cells was also 1 to 2% but in bone marrow from anti-IgD-injected mice donors the frequency was approximately 5%. Cell sorting experiments revealed that all of the capacity to produce IL-4 in response to immobilized IgE or IgG2a or to ionomycin was found in the Fc epsilon R+ fraction. Among the Fc epsilon R+ spleen cells from naive donors, the frequency of IL-4-producing cells was 1/20 to 1/40 whereas in mice that had been injected with anti-IgD or infected with N. brasiliensis, the frequency of IL-4 producing cells in the Fc epsilon R+ population was approximately 1/5.     

Purified and unpurified sodium channels from eel electroplax in planar lipid bilayers

Highly purified sodium channel protein from the electric eel, Electrophorus electricus, was reconstituted into liposomes and incorporated into planar bilayers made from neutral phospholipids dissolved in decane. The purest sodium channel preparations consisted of only the large, 260-kD tetrodotoxin (TTX)-binding polypeptide. For all preparations, batrachotoxin (BTX) induced long-lived single-channel currents (25 pS at 500 mM NaCl) that showed voltage-dependent activation and were blocked by TTX. This block was also voltage dependent, with negative potentials increasing block. The permeability ratios were 4.7 for Na+:K+ and 1.6 for Na+:Li+. The midpoint for steady state activation occurred around -70 mV and did not shift significantly when the NaCl concentration was increased from 50 to 1,000 mM. Veratridine-induced single-channel currents were about half the size of those activated by BTX. Unpurified, nonsolubilized sodium channels from E. electricus membrane fragments were also incorporated into planar bilayers. There were no detectable differences in the characteristics of unpurified and purified sodium channels, although membrane stability was considerably higher when purified material was used. Thus, in the eel, the large, 260-kD polypeptide alone is sufficient to demonstrate single-channel activity like that observed for mammalian sodium channel preparations in which smaller subunits have been found.