Epithelial impedance analysis in experimentally induced colon cancer.

Epithelial impedance analysis was used to measure the alterations in resistance of the large bowel in a murine model of large bowel cancer. The technique was able to resolve the epithelial resistance from the total resistance of the bowel wall. A progressive decrease in resistance of the bowel epithelium occurs during carcinogenesis induced with dimethyhydrazine. About a 21% decrease in epithelial resistance from 22.0 +/- 1.3 omega.cm-2 to 17.5 +/- 1.1 omega cm-2 (p less than 0.025) was observed after 20 wk of carcinogen administration. The sensitivity of the technique in detecting altered epithelial resistance in premalignant bowel mucosa was improved by examining the impedance profile in a sodium-free Ringer's solution where the epithelium of control colons had a resistance of 24.4 +/- 1.8 omega.cm-2 compared with 19.0 +/- 1.1 omega.cm-2 (p less than 0.02) in colons from animals treated for only 4 wk with the carcinogen. Epithelial impedance analysis would seem to be a sensitive technique capable of identifying changes in the electrical properties or the large bowel early in disease states.     

The Influence of Nonautonomous P Elements on Hybrid Dysgenesis in Drosophila melanogaster

An inbred line of the M' strain Muller-5 Birmingham was studied for its abilities to affect P-M hybrid dysgenesis. This strain possesses 57 P elements, all of which are apparently defective in the production of the P transposase. In combination with transposase-producing elements, these nonautonomous elements can enhance or diminish the incidence of hybrid dysgenesis, depending on the trait that is studied. Dysgenic flies that have one or more paternally-derived chromosomes with these elements partially repress the instability of the P element insertion mutation, snw; however, such flies have elevated frequencies of another dysgenic trait, GD sterility, and also show distorted segregation ratios. An explanation is presented in which all of these phenomena are unified as manifestations of the kinetics of P element activation in the germ line. The progeny of Muller-5 Birmingham females exhibit partial repression of both snw instability and GD sterility. This repression appears to involve a factor that can be transmitted maternally through at least two generations. This mode of repression therefore conforms to the pattern of inheritance of the P cytotype, the condition that brings about nearly total repression of P element activity in some strains. Models in which this repression could arise from the nonautonomous P elements of Muller-5 Birmingham are discussed.     

A new mutant class of soybean lacks urease in leaves but not in leaf-derived callus or in roots

Summary We reported earlier the recovery of two classes of soybean urease mutants in soybean (Glycine max L. Merr. cv. Williams). Class I mutants lack the embryo-specific urease while class II mutants lack the activities of both urease isozymes, the embryo-specific and the ubiquitous urease, the latter found in all tissues examined. We report here the recovery of a true-breeding mutant, aj3, which represents the third phenotypic class: normal levels of embryo-specific urease and little or no ubiquitous urease. Unlike class II mutant plants which lack urease in all tissue, aj3 lacks urease activity only in leaves (ca. 2% normal activity); its roots have near normal urease activity. Callus derived from leaves of aj3 has 14% to 40% the urease activity of Williams 82 callus. This partial reduction in urease activity in aj3 callus is sufficient to reduce growth with urea as sole nitrogen source and to confer resistance to 50 mM urea added to callus maintenance medium. Leaves of aj3 produce more than 40 times the urease antigen expected from their urease activity. The aj3 trait is due to a single recessive lesion which is not allelic with lesions at theEu2, Eu3 (class II) orEu1 (class I) loci. We designate the aj3 genotype aseu4/eu4.     

An assessment of the behavioral toxicity of high-energy iron particles compared to other qualities of radiation

Conditioned taste aversion was used to evaluate the behavioral toxicity of exposure to high-energy iron particles (56Fe, 600 MeV/amu) in comparison to that of gamma photons (60Co), high-energy electrons, or fission neutrons. Exposure to high-energy iron particles (5-500 cGy) produced a dose-dependent taste aversion with a maximal effect achieved with a dose of 30 cGy. Gamma photons and electrons were the least effective stimuli for producing a conditioned taste aversion, with a maximal aversion obtained only after exposure to 500 cGy, while the effectiveness of fission neutrons was intermediate to that of photons and iron particles, and a maximal aversion was obtained with a dose of 100 cGy. In the second experiment, rats with lesions of the area postrema were exposed to iron particles (30 cGy), but failed to acquire a taste aversion. The results indicate that (1) high-energy iron particles are more toxic than other qualities of radiation and (2) similar mechanisms mediate the behavioral toxicity of gamma photons and high-energy iron particles.     

Molecular dynamics of antitumor ether-linked phospholipids in model membranes: a spin-label study

We have synthesized a spin-labeled derivative of ET-18-OCH3, a known antitumor ether-linked phospholipid. The spin-labeled analog was shown to be as potent as ET-18-OCH3 in inhibiting 3H-thymidine uptake of HL60 leukemic cells. Electron spin resonance (ESR) studies showed that the mobility of this ether-linked phospholipid in the membrane is more restricted when compared to its ester-linked counterparts. It is probable that the absence of the bulky carbonyl oxygens allows closer packing of the two alkyl chains in the ether-linked phospholipid, thereby reducing the angular amplitude of the motion of the alkyl chains. These findings may be of importance in elucidating mechanisms by which the antitumor ether-linked phospholipids perturb the structure of cellular membranes.     

Book Review

Book Reviewin this Article:
Diabetic Neuropathy edited by P. J. Dyck, P. K. Thomas, A. K. Asbury, A. I. Winegrad, and D. Porte, Jr.     

Consequences of a mixed reproductive system in the hog peanut,Amphicarpaea bracteata, (Fabaceae)

Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.