Monitoring of total chromium in rat fluids and lymphocytes following intratracheal administration of soluble trivalent or hexavalent chromium compounds

1. Intratracheal instillation of sodium dichromate (CrVI) and chromium acetate hydroxide (CrIII) to male Wistar rats gave rise to increased chromium concentrations in whole blood, plasma and urine up to 72 h post exposure; peak concentrations were reached at 6 h after exposure. 2. The ratio of whole blood chromium to plasma chromium concentrations was significantly different for Cr(VI) and Cr(III) treatments. Both blood chromium and plasma chromium assays should therefore be used for the assessment of chromium exposure. 3. Chromium was also detected in peripheral lymphocytes. Cr(VI), but not Cr(III) accumulated significantly in the lymphocytes after treatment. These cells have potential to be used for biomarkers of the assessment of exposure to chromium compounds.

Phenotypes of cytoskeletal mutants

Phenotypic studies continue to contribute to an understanding of the functions of cytoskeletal proteins. Many of these studies indicate some degree of functional redundancy within a family of cytoskeletal proteins. Some surprises have emerged, such as suggestions of unexpected relationships between the actin and microtubule cytoskeletons. Finally, phenotypic studies have provided evidence for a function of intermediate filaments.

Binding of lead to a metallothionein-like protein in human erythrocytes

We have studied the erythrocytes from 24 workers occupationally exposed to inorganic lead, one asymptomatic lead worker showing exceptionally high exposure, and eight control subjects (blood lead 300-750, 1800, and < 100 micrograms/L, respectively). High performance protein chromatography, electrophoresis, and trace metal analysis have identified a low M.Wt., copper, and zinc-containing protein in all cases. This protein (designated protein M) bound lead on in vitro incubation with buffered lead nitrate. Purified samples of protein M were found to show characteristics consistent with metallothionein (M.Wt. approximately 6500, low pI, and greater UV absorbance at 254 nm). Amino acid analysis found a composition of 33% cysteine but no aromatic amino acids. The highly exposed subject showed endogenous lead binding to protein M, which on further purification by ion exchange was found to be associated with one particular constituent (protein M5). Protein M5 was present in much lower quantities in control subjects. These findings suggest the existence of a metallothionein-like protein in erythrocytes which binds lead, sequestering it into a nonbioavailable form and hence protects against lead toxicity.

Caffeine or theophylline for neonatal apnoea?

Caffeine, in the dose usually recommended (12.5 mg/kg loading dose and 3 mg/kg daily maintenance), and a higher dose regimen (25 mg/kg loading and 6 mg/kg daily maintenance), was compared with theophylline (7.5 mg/kg loading and 3 mg/kg thrice daily maintenance). The study was a randomised controlled trial in the treatment of a group of 44 infants of less than 31 weeks' gestation (mean gestational age 28.3 weeks) who were suffering from frequent apnoeic attacks. All three regimens produced a significant reduction in apnoeic attacks within 24 hours, but only the higher dose caffeine and theophylline groups showed a significant improvement in apnoea within eight hours. The use of caffeine for the treatment of neonatal apnoea is recommended, because a once daily dose is more easily administered, and because it was found that plasma concentrations were more predictable than those of theophylline. If used in very preterm infants, however, its is suggested that a higher dose regimen than that previously recommended be used to achieve a faster response.

Suppression of a myosin defect by a kinesin-related gene

Motor proteins in cells include myosin, which is actin-based, and kinesin, dynein and dynamin, which are microtubule-based. Several proteins have recently been identified that have amino-acid sequences with similarity to the motor domains of either myosin or kinesin, but are otherwise dissimilar. This has led to the suggestion that these may all be motor proteins, but that they are specialized for moving different cargos. Genetic analysis can address the question of the different functions of these new proteins. Studies of a temperature-sensitive mutation (myo2-66) in a gene of the myosin superfamily (MYO2) have implicated the Myo2 protein (Myo2p) in the process of polarized secretion in yeast (Saccharomyces cerevisiae). To understand more about the role of Myo2p, we have looked for 'multicopy suppressors' (heterologous genes that, when overexpressed, can correct the temperature sensitivity of the myo2-66 mutant). Here we report the identification of such a suppressor (SMY1) that (surprisingly) encodes a predicted polypeptide sharing sequence similarity with the motor portion of proteins in the kinesin superfamily.

Induction of DNA strand breaks in peripheral lymphocytes by soluble chromium compounds

1. Incubation of human lymphocytes with sodium dichromate (CrVI) at 37 degrees C for 3 h resulted in a dose-dependent increase in DNA strand breaks without concurrent cytotoxicity. In contrast, chromium acetate hydroxide (CrIII) failed to induce DNA strand breaks at sub-cytotoxic concentrations. 2. DNA strand breaks were also detected in the peripheral lymphocytes of Wistar rats, 24 h after intratracheal instillation of sodium dichromate (1.3 and 2.5 mg kg-1). Instillation of chromium acetate hydroxide (up to 21.8 mg kg-1) failed to induce DNA strand breaks in peripheral lymphocytes. In accord with previous studies, hexavalent chromium was found to be more readily absorbed from the lungs into the peripheral blood than chromium in its trivalent form. 3. The results of this study indicate that fluorometric analysis of DNA unwinding (FADU) in peripheral lymphocytes might be a convenient method of measuring an important biological effect of chromium in occupationally-exposed workers.

Spatial and temporal control of nonmuscle myosin localization: identification of a domain that is necessary for myosin filament disassembly in vivo

Myosin null mutants of Dictyostelium are defective for cytokinesis, multicellular development, and capping of surface proteins. We have used these cells as transformation recipients for an altered myosin heavy chain gene that encodes a protein bearing a carboxy-terminal 34-kD truncation. This truncation eliminates threonine phosphorylation sites previously shown to control filament assembly in vitro. Despite restoration of growth in suspension, development, and ability to cap cell surface proteins, these delta C34-truncated myosin transformants display severe cytoskeletal abnormalities, including excessive localization of the truncated myosin to the cortical cytoskeleton, impaired cell shaped dynamics, and a temporal defect in myosin dissociation from beneath capped surface proteins. These data demonstrate that the carboxy-terminal domain of myosin plays a critical role in regulating the disassembly of the protein from contractile structures in vivo.

Purification of profilin from Saccharomyces cerevisiae and analysis of profilin-deficient cells

We have isolated profilin from yeast (Saccharomyces cerevisiae) and have microsequenced a portion of the protein to confirm its identity; the region microsequenced agrees with the predicted amino acid sequence from a profilin gene recently isolated from S. cerevisiae (Magdolen, V., U. Oechsner, G. Müller, and W. Bandlow. 1988. Mol. Cell. Biol. 8:5108-5115). Yeast profilin resembles profilins from other organisms in molecular mass and in the ability to bind to polyproline, retard the rate of actin polymerization, and inhibit hydrolysis of ATP by monomeric actin. Using strains that carry disruptions or deletions of the profilin gene, we have found that, under appropriate conditions, cells can survive without detectable profilin. Such cells grow slowly, are temperature sensitive, lose the normal ellipsoidal shape of yeast cells, often become multinucleate, and generally grow much larger than wild-type cells. In addition, these cells exhibit delocalized deposition of cell wall chitin and have dramatically altered actin distributions.

Antenatal urinary screening for drugs of addiction: usefulness of sideroom testing?

Based on a pilot study of 400 samples at our Antenatal Clinic (which yielded 3.5% positives when assessed for amphetamines, cannabinoids and opiates) 600 consecutive patients attending Antenatal Booking Clinic had urine samples tested in the sideroom for amphetamines, barbiturates, cocaine metabolites, methadone and opiates using the Syva EMIT ETS apparatus. Positive samples were checked in the West Midlands Regional Laboratory for Toxicology, initially by EMIT-dau on a second ETS instrument and then by thin layer and gas chromatography. Two per cent produced a total of 14 positive EMIT results. Cocaine metabolites and methandone were not detected. Four specimens could not be confirmed as positive. In one sample, amphetamine-like compounds were isolated but not identified. Positive identification was made in the remaining seven specimens (two cannabinoid, two pseudoephedrine, one pseudoephedrine plus dihydrocodeine and two dihydrocodeine). There was a serious problem of false positive results observed in the initial sideroom testing. The value of sideroom testing for drugs of abuse was assessed in relation to the technical problems and to the small rate of drug positive samples.

Hygromycin resistance as a selectable marker in Dictyostelium discoideum

We have constructed an expression cartridge which has the bacterial hygromycin resistance gene (hph) fused to the Dictyostelium discoideum actin 15 promoter, with a segment of 3'-flanking DNA from the actin 15 locus placed downstream of the hph gene to serve as a transcription terminator. The plasmid pDE109, which contained this cartridge and a Dictyostelium origin of replication, transformed D. discoideum with high efficiency under hygromycin selection. The availability of this selectable marker circumvents the previous limitation of having G418 resistance as the only selectable marker for this organism; secondary transformation can now be used to introduce DNA into previously transformed cell lines.

Successful periodontal treatment for the elderly

The demographic reality of a rapidly growing elderly population segment presents the practicing dentist with certain imperatives and challenges. Familiarity with the healthy aging process and common medical conditions of the aged is becoming increasingly essential. Customized treatment plans and modifications in techniques and home care aids require flexibility and creativity. In addition, it should not be overlooked that this demographic reality also presents the practicing dentist with new opportunities for practice-building as well as personal and professional satisfaction.

Clinical and sub-clinical lead poisoning: a laboratory perspective

1. The background, scope and limitations of laboratory methods for the diagnosis of inorganic lead poisoning are outlined in the context of the work of a specialist clinical laboratory for trace element analysis. 2. Data for blood lead, haemoglobin and erythrocyte zinc protoporphyrin concentrations are presented in cases of clinical and sub-clinical poisoning due to accidental or occupational exposure. 3. Data from population surveys of children and adults subject to either environmental or occupational exposure are also shown. 4. In general, analysis for lead in an appropriate specimen of blood offers the single most useful index of exposure. 5. The importance of good accuracy control in such measurements is emphasized.

Blood lead, ethnic origin, and lead exposure

A survey of blood lead concentrations is reported in a group of 199 young Walsall children (3-6 years of age). The geometric mean blood lead concentration was 0.47 mumol/l (range 0.2-1.6 mumol/l). There were no significant differences in blood lead concentrations between groups of children with different ages, sex, ethnic origin, or environment.

Artifactual immunofluorescent labelling in yeast, demonstrated by affinity purification of antibody

In the course of making antibodies against various yeast (S. cerevisiae) proteins, we have noted that it is common to observe reactivity of rabbit sera with a number of extraneous bands on Western transfers of yeast proteins. The pattern of reactive bands can change within a period of weeks, even when the rabbit has not been injected with antigen. A simple method of affinity purification, using antigen bound to nitrocellulose, is employed to remove the reactivity with these extraneous bands from immune sera. The importance of affinity purification is demonstrated by our attempts to immunolocalize a 55 kd yeast protein (p55). Immune serum stains yeast cells to give a striking pattern of spots and blotches not seen with preimmune serum. However, affinity purification of anti-p55 antibody shows that this pattern is not due to staining by anti-p55 antibody; rather the pattern is due to staining left in the serum depleted of anti-p55 antibody.

Using antibodies against Dictyostelium membranes to identify an actin-binding membrane protein

Polyclonal antibodies made against Dictyostelium discoideum membranes were used to block the interaction of those membranes with actin. As expected, actin interacted mostly with the internal surface of the membrane, demonstrated by the fact that whole cells could only absorb out a minor fraction of the blocking antibody. The antibody was used to show that the membrane component(s) which interacted with actin were probably integral; they could be extracted with detergent but not with solutions designed to extract peripheral membrane proteins. To identify the responsible protein(s), Western transfers of membranes were cut into fractions which were tested for their ability to absorb out the blocking activity of the antibody. We observed a single peak at a molecular weight of approximately 20,000, and thus conclude that a 20,000-mol-wt protein is a major integral membrane actin-binding protein in Dictyostelium. This approach to the identification of proteins involved in actin-membrane interaction has allowed us to make the first identification of an actin-binding membrane protein which is based on its activity in native membranes.

Isolation of an actin-binding protein from membranes of Dictyostelium discoideum

We prepared a probe of radiolabeled, glutaraldehyde cross-linked filamentous actin (F-actin) to study binding of actin to membranes of Dictyostelium discoideum. The probe bound to membranes or detergent extracts of membranes with a high affinity and in a saturable manner. The binding could be reduced by boiling of either the actin probe or the membranes, or by addition of excess native F-actin, but not by addition of an equivalent amount of bovine serum albumin, to the assay. The probe labeled several proteins when used to overlay sodium dodecyl sulfate gels of Dictyostelium membranes. One of these labeled proteins was a 24,000-mol-wt protein (p24), which was soluble only in the presence of a high concentration of sodium deoxycholate (5%, wt/vol) at room temperature or above. The p24 was purified by selective detergent extraction and column chromatography. When tested in a novel two-phase binding assay, p24 bound both native monomeric actin (G-actin) and F-actin in a specific manner. In this assay, G-actin bound p24 with a submicromolar affinity.

A Ca2+ insensitive actin-crosslinking protein from Dicytostelium discoideum

We have isolated a 30,000-dalton protein from Dictyostelium which cosedimented with and affected the low shear viscosity of actin. At low concentrations, this protein increased the low shear viscosity to greater than that of the actin control, whereas higher concentrations decreased viscosity. The viscosity decrease correlated with the formation of actin filament bundles, as seen electron microscopically. This protein resembled a previously reported actin-binding protein from Dictyostelium [Fechheimer and Taylor, 84, J Biol Chem 259:4514] in electrophoretic mobility, Stokes radius, and ability to crosslink filaments, but was shown to be different by peptide mapping, lack of immunologic crossreactivity, and lack of sensitivity to calcium.