Analysis of low concentrations of 5-bromo-2-deoxyuridine on sister chromatid exchanges in human lymphocytes

To determine a concentration of 5-bromo-2-deoxyuridine (BrdU) sufficient for sister chromatid differentiation (SCD), and yet having a minimal effect on the number of sister chromatid exchanges (SCEs), we assessed the effect produced on the number of SCEs by low concentrations (1, 3, and 10 micrograms/mL) of BrdU. SCD was not obtained in 19% of the 31 subjects with 1 microgram/mL of BrdU, while the differentiation was adequate for all samples treated with 3 and 10 micrograms/mL. We statistically analysed the effects of these three different doses and found no significant difference in the number of SCEs obtained with the doses of 1 and 3 micrograms/mL, but a significant difference was observed between these two concentrations and 10 micrograms/mL. We therefore suggest that the dose of 3 micrograms/mL, while sufficient to produce reliable differential staining, still permits an adequate evaluation of the base line of SCEs and appears to enhance the sensitivity of the test to evaluate between-individual variations. Our experiments also underline that SCE counts should include the centromere exchanges.     

Dynamic G- and R-banding of human chromosomes for electron microscopy

Synchronized human lymphocytes were exposed to 5-bromo-2-deoxyuridine (BrdUrd) for incorporation in either G-or R-bands. The substituted bands were revealed by monoclonal anti-BrdUrd antibodies disclosed with either gold-labeled antibodies or with the protein A-gold complex. Sharp G-or R-banding, specific for electron microscopy (EM), was obtained. These banding patterns, referred to as GB-AAu (G-bands by BrdUrd using Antibodies and gold [Au]) and RB-AAu (R-bands by BrdUrd using Antibodies and gold [Au]), resemble dynamic band patterns (GBG and RBG) much more than they do morphologic band patterns (GTG and RHG). The G- and R- band patterns allow accurate chromosome identification and karyotyping. An actual karyotype of human GB-AAu-banded chromosomes at the 750 band level, photographed in the EM, is presented. The method produces excellent band separation and band contrast. Variations in band staining intensities were noted and correlated with BrdUrd enrichment. The C-band regions were positively stained after GB-AAu banding while they were negatively stained after RB-AAu banding. Telomeres appeared heterogeneous after GB-AAu banding suggesting that part of the telomeric bands might be late replicating.     

High-resolution dynamic and morphological G-bandings (GBG and GTG): a comparative study

Summary A high-resolution replication banding technique, dynamic GBG banding (G-bands after 5-bromodeoxyuridine [BrdUrd] and Giemsa), showed that, at a resolution of 850 bands/genome, GBG banding and GTG banding (G-bands after trypsin and Giemsa) produce almost identical patterns. RBG band (R-bands after BrdUrd and Giemsa) and RHG band (R-bands after heat denaturation and Giemsa) patterns were previously shown to be only 75%–85% coincident; thus GTG banding more accurately reflects replication patterns than does RHG banding. BrdUrd synchronization uses high concentrations of BrdUrd both to substitute early replicating DNA and to arrest cells before the late bands replicate. Release from the block is via a low thymidine concentration. The banding is revealed by the fluorochrome-photolysis-Giemsa (FPG) technique and produces the GBG banding that includes concomitant staining of constitutive heterochromatin. As opposed to other replication G-banding procedures, BrdUrd synchronization and GBG banding produces a reproducible replication band pattern. The discordance between homologs after GBG banding is similar to that after GTG banding and no lateral asymmetry of the constitutive heterochromatin has been observed. Also, BrdUrd synchronization neither significantly depresses the mitotic index, nor induces chromosome breaks. Thus, GBG banding seems as clinically useful as GTG banding and provides important information regarding replication time.     

Endocytosis of an antibody ricin A-chain conjugate (immuno-A-toxin) adsorbed on colloidal gold. Effects of ammonium chloride and monensin

An immunotoxin (IT) formed by a specific antibody coupled to the ricin A chain was adsorbed on colloidal gold particles (IT-Au). Binding and internalization of IT-Au in human lymphoblastic CEM cells were studied using electron microscopy. IT-Au showed specific cytotoxic activity toward the target cells. After 1 h at 4 degrees C, IT-Au were linked diffusely to the plasma membrane with 45% of the particles regrouped in clusters. Upon transfer to 37 degrees C, the particles carrying the ligand were regrouped more frequently and internalized into the cell by endocytosis through smooth microinvaginations or coated pits of the plasma membrane. After 15 min, IT-Au was observed in endocytic vacuoles, or receptosomes, in tubular structure near the Golgi apparatus and in lysosomes. Entry of IT-Au into lysosomes was rapid (around 50% of intracellular IT-Au particles after 30 min). NH4Cl or monensin, well-known potentiators of immunotoxin activity, when present in incubation medium, altered neither the processes nor the rate of IT-Au endocytosis. In the presence of either of these substances, IT-Au accumulated in the normal or often enlarged endocytic vacuoles, and entry into the lysosomes was slowed down (50% of particles after 2 h 15 min). We conclude that this intense slowing-down in the speed of IT-Au transportation into lysosomes and the functional modifications of these organelles help to explain the increased efficacy of immunotoxins in the presence of potentiators.     

Cardiovascular and biological effects of K+ channel openers, a class of drugs with vasorelaxant and cardioprotective properties

Several new chemical entities (RP 52891, cromakalim and its derivatives) are potent and specific openers of vascular K+ channels. This mechanism is also shared, at least partially, by drugs such as minoxidil, diazoxide, pinacidil and nicorandil. The opening of plasmalemma K+ channels produces loss of cytosolic K+. This effect results in cellular hyperpolarization and functional vasorelaxation. In normotensive or hypertensive rats, K+ channel activators decrease aortic blood pressure (by producing a directly mediated fall in systemic vascular resistance) and reflexly increase heart rate. The former effect is not modified by specific blockers of classical vascular receptors but it is completely antagonized by the hypoglycemic sulphonylurea, glibenclamide, an established blocker of ATP-regulated K+ channels. K+ channel openers produce selective coronary vasodilatation and afford functional and biochemical protection to the ischemic myocardium. This salutary effect is mediated via cardiac K+ channel modulation and may result from an improved myocardial oxygen balance in the ischemic region. K+ channel openers increase plasma renin activity in animals as well as in man. However, only diazoxide, but not cromakalim or RP 52891, lowers plasma insulin concentration. The dose of glibenclamide entirely blocking the latter effect is over 50-fold smaller than that antagonizing the hypotensive and hyper-reninemic responses to diazoxide. In conclusion, K+ channel activators are potent vasorelaxant and cardioprotective agents possessing an original mechanism of action which is the opening of plasmalemma ATP-regulated K+ channels. Their clinical use as antihypertensive agents may be accompanied by undesirable effects (characteristic of peripheral vasodilators) which are likely to be attenuated or avoided by controlled release formulations. However, inasmuch as low doses of K+ channel openers may be sufficient to produce selective coronary artery dilatation and cardioprotection, these compounds could be of particular value in treating patients with coronary artery disease efficaciously and possibly without adverse cardiovascular effects.     

Evolution of mouse B1 repeats: 7SL RNA folding pattern conserved

Summary In a recent report mouse B1 genomic repeats were divided into six families representing different waves of fixation of B1 variants, consistent with the retroposition model of human Alu elements. These data are used to examine the distribution of nucleotide substitutions in individual genomic repeats with respect to family consensus sequences and to compare the minimal energy structures of the corresponding B1 RNAs. By an enzymatic approach the predicted structure of B1 RNAs is experimentally confirmed using as a model sequence an RNA of a young B1 family member transcribed in vitro by T7 RNA polymerase. B1 RNA preserves folding domains of the Alu fragment of 7SL RNA, its progenitor molecule. Our results reveal similarities among 7SL-like retroposons, human Alu, and rodent B1 repeats, and relate the evolutionary conservation of B1 family consensus sequences to selection at the RNA level.     

Incidence of hepatitis non-A,non-B compared with types A and B in hospital patients.

To establish the relative frequencies of types A, B and non-A, non-B hepatitis, stored samples of blood from all the cases of acute viral hepatitis seen over a period of 9 years in a general hospital for adults were classified according to their type by presently available serologic methods. The study included 456 episodes of hepatitis in 447 patients, distributed as follows: 114 episodes of hepatitis A (25%), 282 of hepatitis B (62%) and 60 of hepatitis non-A, non-B (13%). The episodes of non-A, non-B hepatitis were equally distributed between the sexes, suggesting a mode of transmission different from that of hepatitis A or B, which had male/female ratios of 2.4 and 3.1 respectively. The low proportion of hepatitis non-A, non-B may not reflect its real frequency, since it often escapes clinical recognition.