Specificity of gentamicin accumulation by rat renal cortex.

The accumulation of gentamicin by rat renal cortex $\text{in}$$\text{vivo}$ and $\text{in}$$\text{vitro}$ was not inhibited by probenecid, tetraethylammonium, cephalosporins nor α-aminoisobutyric acid, but was significantly blocked by other aminoglycosides (neomycin, tobramycin and kanamycin). The data suggest that specific binding sites for aminoglycosides are present on the surface or in cells of the renal proximal tubule.     

Determination of the molecular mass of bacterial genomic DNA and plasmid copy number by high-pressure liquid chromatography

Relatively rapid methods for the determination of relative genome molecular mass (Mr) and the estimation of plasmid copy number have been developed. These methods are based on the ability of the Bio-Rad high-pressure liquid chromatography hydroxylapatite column to separate and quantify single-stranded DNA, double-stranded DNA, and plasmid DNA. Genome Mr values were calculated from reassociation kinetics of single-stranded DNA as measured with the hydroxylapatite column. Bacteriophage T4 DNA was used to establish a C0t (moles of nucleotides times seconds per liter), or standard reassociation value. From this C0t value, C0t values for Escherichia coli B, Beggiatoa alba B18LD, and Streptomyces coelicolor were determined by comparative calculations. From those calculated C0t values, the Mr values of 1.96 X 10(9) for E. coli, 2.02 X 10(9) for B. alba, and 3.28 X 10(9) for S. coelicolor were estimated. Plasmid concentration was determined from cleared lysates by comparing the integrated area under the phosphate buffer-eluted plasmid peak to values obtained with known amounts of plasmid. The plasmid copy number was estimated by multiplying the ratio between the amounts of plasmid and chromosomal DNA by the ratio between the Mr values of the chromosome and the plasmid. A copy number of 29 was obtained from a culture of E. coli HB101 harboring pBR322 grown to a culture density of 1.6 X 10(9) CFU . ml-1.     

Issues in analysis of data on paternal age and 47,+21: implications for genetic counseling for Down syndrome

Summary Data and analyses on paternal age and 47,+21 are reviewed. It is concluded that there are few, if any, grounds to justify the inference of a paternal age effect independent of maternal age for those paternal age-maternal age combinations on which there are prenatal diagnostic data. It is suggested that genetic counseling as to increased (or decreased) risk of Down syndrome associated with various paternal ages is not justified at present.     

Biochemical mechanisms of cephaloridine nephrotoxicity

Large doses of the cephalosporin antibiotic, cephaloridine, produce acute proximal tubular necrosis in humans and in laboratory animals. Cephaloridine is actively transported into the proximal tubular cell by an organic anion transport system while transport across the lumenal membrane into tubular fluid appears restricted. High intracellular concentrations of cephaloridine are attained in the proximal tubular cell which are critical to the development of nephrotoxicity. There is substantial evidence indicating that oxidative stress plays a major role in cephaloridine nephrotoxicity. Cephaloridine depletes reduced glutathione, increases oxidized glutathione and induces lipid peroxidation in renal cortical tissue. The molecular mechanisms mediating cephaloridine-induced oxidative stress are not well understood. Inhibition in gluconeogenesis is a relatively early biochemical effect of cephaloridine and is independent of lipid peroxidation. Furthermore, cephaloridine inhibits gluconeogenesis in both target (kidney) and non-target (liver) organs of cephaloridine toxicity. Since glucose is not a major fuel of proximal tubular cells, it is unlikely that cephaloridine-induced tubular necrosis is mediated by the effects of this drug on glucose synthesis.     

Localization and sequence analysis of poly(A) sites generating multiple dihydrofolate reductase mRNAs

The murine dihydrofolate reductase (DHFR) gene gives rise to multiple polyadenylated mRNAs displaying heterogeneity in the length of the 3' untranslated region. These species are present in the cytoplasm at levels that vary over 2 orders of magnitude, suggesting that certain poly(A) sites are preferred over others. Previous observations have shown that three out of the four major sites of polyadenylation do not display consensus hexanucleotide (AATAAA, ATTAAA) signals. We have further analyzed the sequences involved in directing multiple polyadenylation events on the DHFR gene by focusing our attention on the 4.1- and 5.6-kilobase mRNAs, the lowest abundance DHFR species observed on RNA blot analysis. Identification and sequence analysis of the poly(A) addition sites corresponding to these species revealed appropriately positioned consensus hexanucleotide signals; additional nearby poly(A) sites were also detected which apparently do not use consensus hexanucleotides to direct poly(A) addition to DHFR mRNAs of relatively lower abundance. We have also identified polyadenylation sites downstream of the 4.1- and 5.6-kilobase sites which display consensus hexanucleotide signals and correspond to messenger species too rare for detection by routine RNA blot analysis. Our data bring to 11 the number of known functional poly(A) addition sites associated with the DHFR gene.     

Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe

Small-scale spatial heterogeneity of soil organic matter (SOM) associated with patterns of plant cover can strongly influence population and ecosystem dynamics in dry regions but is not well characterized for semiarid grasslands. We evaluated differences in plant and soil N and C between soil from under individual grass plants and from small openings in shortgrass steppe. In samples from 0 to 5 cm depth, root biomass, root N, total and mineralizable soil N, total and respirable organic C, C:N ratio, fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants than soil from openings. These differences, which were consistent for two sites with contrasting soil textures, indicate strong differentiation of surface soil at the scale of individual plants, with relative enrichment of soil under plants in total and active SOM. Between-microsite differences were substantial relative to previously reported differences associated with landscape position and grazing intensity in shortgrass steppe. We conclude that microscale heterogeneity in shortgrass steppe deserves attention in investigation of controls on ecosystem and population processes and when sampling to estimate properties at plot or site scales.     

Maternal cigarette smoking, Down syndrome in live births, and infant race.

Previous studies have suggested that maternal smoking is negatively associated with a Down syndrome live birth. We analyzed the data of the U.S. Perinatal Collaborative Study in a search for racial variation in Down syndrome risk factors. There were 22 cases in 25,346 live births to smoking mothers (4/10,780 blacks, 18/13,320 whites, and 0/1,246 other races) and 42/29,130 live births to nonsmoking mothers (24/14,665 blacks, 14/11,694 whites, and 4/2,771 others). The crude overall rates per 1,000 live births were 0.4 in black smokers and 1.6 in black nonsmokers but 1.4 in white smokers and 1.2 in white non-smokers. Adjusted for maternal age, the summary relative risk for a Down syndrome live birth to a smoking mother was 0.2 in blacks (95% interval 0.1-0.7) but 1.2 in whites (95% interval 0.6-2.5). Stratification on variables associated with socioeconomic status or gestational age at time of entry into the study did not alter the racial difference. A comparison of smokers with those who never smoked revealed essentially the same trends. Among all nonsmokers the ratio of the maternal age-adjusted risks for a Down syndrome live birth in whites compared with blacks was 0.7 (95% interval 0.3-1.3), and among all smokers this ratio was 3.6 (95% interval 1.3-9.9). If the results are not attributable to statistical fluctuation or undetected confounding, then differences in the probability of intrauterine survival of the Down syndrome fetus would appear to be one plausible explanation for the difference.