RADIOAUTOGRAPHY OF CHOLESTEROL IN LUNG : An Assessment of Different Tissue Processing Techniques

30 Swiss albino mice aged 8 days were injected intraperitoneally with 0.2 ml of a solution of 4% N,N-dimethyl-formamide in 5% dextrose in water containing cholesterol-1,2-³H (~1 mCi/ml). Lung tissue was embedded in an Epon mixture after either acetone and propylene oxide dehydration, partial ethanol and Epon 812 dehydration, or the precipitation of cholesterol by digitonin succeeded by partial dehydration. The distribution of cholesterol-1,2-³H in lung parenchyma in 1µ Epon section radioautograms was compared with that in frozen section radioautograms and was found to be independent of the manner of tissue processing. Grain distribution in the tissue was essentially the same whether 16, 63, 93, or 100% radioactivity was retained in the lung. However, grain distribution in the alveolar spaces differed, presumably due to displacement of pulmonary surfactant, which contains cholesterol. Intracellular distribution of cholesterol, in electron microscope radioautograms, was the same with either 51% or 93% retention of radioactivity in the lung. Loss of radioactivity into the various processing solutions was monitored. The various processing techniques have different drawbacks.     

S-Potentials in the Skate Retina : Intracellular recordings during light and dark adaptation

The S-potentials recorded intracellularly from the all-rod retina of the skate probably arise from the large horizontal cells situated directly below the layer of receptors. These cells hyperpolarize in response to light, irrespective of stimulus wavelength, and the responses in photopic as well as scotopic conditions were found to be subserved by a single photopigment with λ_max = 500 nm. The process of adaptation was studied by recording simultaneously the threshold responses and membrane potentials of S-units during both light and dark adaptation. The findings indicate that the sensitivity of S-units, whether measured upon steady background fields or in the course of dark adaptation, exhibits changes similar to those demonstrated previously for the ERG b-wave and ganglion cell discharge. However, the membrane potential level of the S-unit and its sensitivity to photic stimulation varied independently for all the adapting conditions tested. It appears, therefore, that visual adaptation in the skate retina occurs before the S-unit is reached, i.e., at the receptors themselves.     

Equivalent Circuit of Frog Atrial Tissue as Determined by Voltage Clamp-Unclamp Experiments

The equivalent circuit that has been used in the analysis of nerve voltage-clamp data is that of the membrane capacity in parallel with the membrane resistance. Voltage-clamp experiments on frog atrial tissue indicate that this circuit will not suffice for this cardiac tissue. The change in membrane current associated with a step change in membrane potential does not show a rapid spike of capacitive current as would be expected for the simple parallel resistance-capacitance network. Rather, there is a step change in current followed by an exponential decay in current with a time constant of about 1 msec. This relatively slow capacitive charging current suggests that there is a resistance in series with the membrane capacity. A possible equivalent circuit is that of a series resistance external to the parallel resistance-capacitance network of the cell membranes. Another possible circuit assumes that the series resistance is an integral part of the cell membrane. The data presented in this paper demonstrate that the equivalent circuit of a bundle of frog atrial muscle is that of an external resistance in series with the cell membranes.     

The 5-methylcytosine content of DNA: Tissue specificity

Using a new technique for the determination of the extent of DNA methylation by comparing the incorporation of radioactivity from deoxycytidine-2-C¹⁴ into DNA cytosine and 5-methylcytosine (5MC), the 5MC content of DNA was found to be a tissue specific property in two systems: (1) mouse tissue culture cell lines, in which the level of 5MC varied from 2.97 ± 0.03% conversion of cytosine to 5MC in the DNA of a mouse melanoma line to 4.58 ± 0.18% in a primary teratoma line, and (2) the organs of the developing chick embryo, in which the level of 5MC varied from 3.60 ± 0.04% conversion of cytosine to 5MC in the DNA of the chorioallantoic membrane to 4.19 ± 0.02% in the brain.     

Interaction of Pseudomonas Bacteriophage 2 with the Slime Polysaccharide and Lipopolysaccharide of Pseudomonas aeruginosa Strain BI

Purified slime polysaccharide B and lipopolysaccharide of Pseudomonas aeruginosa strain BI were shown to possess receptor-like properties in inactivating Pseudomonas phage 2, whereas lipoprotein and glycopeptide fractions were devoid of activity. On a weight basis, slime polysaccharide B was more effective than lipopolysaccharide in inactivating phage. The specificity of the reaction with slime polysaccharide B was indicated by the fact that slime polysaccharide A of P. aeruginosa strain EI failed to inactivate phage 2. Electron micrographs showed phage 2 in typical, tail-first position of attachment on intact cells of strain BI, slime polysaccharide B, and lipopolysaccharide. Tail fibers were discernible during phage attachment.     

Ribonuclease-Sensitive Deoxyribonucleic Acid Polymerase Activity in Uninfected Rat Cells and Rat Cells Infected with Rous Sarcoma Virus

Rat cells infected with the B77 strain of avian sarcoma virus [R(B77) cells] produced no virus-like particles but contained information for the production of infectious B77 virus. (3)H-labeled deoxyribonucleic acid (DNA) product of the B77 virus endogenous DNA polymerase system was used to determine the relative amounts of B77 virus-specific ribonucleic acid (RNA) in B77 virus-infected chicken and R(B77) cells. R(B77) cells were found to contain much less B77 virus RNA than did B77 virus-infected chicken cells. Ribonuclease-sensitive DNA polymerase activity was present in high-speed pellet fractions from Nonidet extracts of B77 virus-infected rat cells. Similar preparations from some uninfected rat cells contained lesser amounts of a similar ribonuclease-sensitive DNA polymerase activity. The endogenous template for the DNA polymerase activity in high-speed pellet fractions from R(B77) cells was not related to B77 virus RNA or to RNA of a rat C-type virus. The DNA product of the endogenous DNA polymerase in high-speed pellet fractions of R(B77) cells hybridized to a small extent with RNA from the same fraction and to a similar extent with RNA from uninfected rat cells.     

An analysis of the response in phloem exudation on application of massage to Ricinus

Summary A study, made on the phloem exudation profiles from Ricinus plants given varying degrees of pre-treatment by massage, has revealed that the profiles are governed by sealing systems of considerable complexity. One of the most interesting profiles observed involves an initial rapid escape of sap from a single cut which ceases after several minutes, then recommences and builds up prior to a second slow decline; this has been called the rebleed phenomenon. At least two mechanisms must be postulated to explain this profile satisfactorily.Massage pre-treatment seems to enhance potential exudation quite locally; even half an internode may be treated with little influence on adjacent tissue. The induced build up in potential exudation gradually increased over several days and after suspension of massage declined at a comparable rate. Massage during exudation can be used to stop flow but exudation may recommence after a period, resembling the rebleed exudation profile.     

Differential Recovery of Auxotrophs After Penicillin Enrichment in Escherichia coli

Various auxotrophs are recovered from a penicillin enrichment cycle with differing efficiencies. Reconstruction experiments indicate that, under starvation conditions in the presence of penicillin, most auxotrophs undergo some death, whereas prolineless mutants are virtually immune to penicillin-induced killing.     

Microbial Transformation of Antibiotics: Phosphorylation of Clindamycin by Streptomyces coelicolor Müller

Addition of clindamycin to whole-cell cultures of Streptomyces coelicolor Müller resulted in the loss of in vitro activity against organisms sensitive to clindamycin. Incubation of such culture filtrates with alkaline phosphatase generated a biologically active material identified as clindamycin. Fermentation broths containing inactivated clindamycin yielded clindamycin 3-phosphate, the structure of which was established by physical-chemical and enzymatic studies. Clindamycin was phosphorylated by lysates and partially purified enzyme preparations from S. coelicolor Müller. These reactions require a ribonucleoside triphosphate and Mg(2+). The product of the cell-free reactions was identified as clindamycin 3-phosphate.