Pristionchus pacificus, a nematode with only three juvenile stages, displays major heterochronic changes relative to Caenorhabditis elegans

The nematode Pristionchus pacificus (Diplogastridae) has been described as a satellite organism for a functional comparative approach to the model organism Caenorhabditis elegans because genetic, molecular, and cell-biological tools can be used in a similar way in both species. Here we show that P. pacificus has three juvenile stages, instead of the usual four found in other nematodes. Embryogenesis is lengthened and many developmental events that take place during the first juvenile stage in C. elegans occur during late embryogenesis in P. pacificus. Video imaging and transmission electron microscopy revealed no embryonic moult. The timing of later developmental events relative to the moults differs between P. pacificus and C. elegans. In addition, the post-embryonic blast-cell divisions display a specific change in timing between the two species, resulting in heterochrony between different cell lineages, such as vulval and gonadal lineages. Developmental events appear to come into register during the last larval stage. Thus, differences in developmental timing between P. pacificus and C. elegans represent a deep heterochronic change. We designate the three juvenile stages of P. pacificus as J1 to J3. Comparison with other species of the family Diplogastridae indicates that this pattern represents an apomorphic character for the monophylum Diplogastridae.

Refractive index of air. 2. Group index

In a previous paper [Appl. Opt. 35, 1566 (1996)] one of us presented new equations for evaluation of the phase refractive index of air over a range of wavelengths and atmospheric parameters. That paper also gave an incorrect, although sufficiently accurate, procedure for calculating the group refractive index. Here we describe the results of a more rigorous derivation of the group index that takes proper account of the Lorentz-Lorenz formula, and we demonstrate that deviations from the Lorentz-Lorenz formula are insignificant to within a foreseeable precision of dispersion measurements for atmospheric conditions. We also derive and evaluate a simplification of the resultant equation that is useful for exploratory calculations. We clarify the limits of validity of the standard equation for the group refractive index and correct some minor errors in the previous paper.

pos-1 encodes a cytoplasmic zinc-finger protein essential for germline specification in C. elegans

Germ cells arise during early C. elegans embryogenesis from an invariant sequence of asymmetric divisions that separate germ cell precursors from somatic precursors. We show that maternal-effect lethal mutations in the gene pos-1 cause germ cell precursors to inappropriately adopt somatic cell fates. During early embryogenesis, pos-1 mRNA and POS-1 protein are present predominantly in the germ precursors. POS-1 is a novel protein with two copies of a CCCH finger motif previously described in the germline proteins PIE-1 and MEX-1 in C. elegans, and in the mammalian TIS11/Nup475/TTP protein. However, mutations in pos-1 cause several defects in the development of the germline blastomeres that are distinct from those caused by mutations in pie-1 or mex-1. The earliest defect detected in pos-1 mutants is the failure to express APX-1 protein from maternally provided apx-1 mRNA, suggesting that POS-1 may have an important role in regulating the expression of maternal mRNAs in germline blastomeres.

Assessment of foot-to-foot bioelectrical impedance analysis for the prediction of total body water

OBJECTIVE

To investigate the accuracy of foot-to-foot impedance methodology for the prediction of total body water and whether leg length rather than stature should be used in the prediction of total body water.

DESIGN

Cross-sectional study using volunteers from the community.

SETTING

University laboratory.

SUBJECTS

57 subjects (29 male; 28 female) aged 19-56 y.

INTERVENTIONS

Total body water was measured using a deuterium oxide dilution technique. Total body water was also predicted using foot-to-foot impedance apparatus (Tanita Inc, Tokyo, Japan, Model TBF 305).

RESULTS

Mean values for predicted and measured total body water differed by 0.71. However this bias was not constant across all individuals with a progressive underestimation of total body water by foot-to-foot impedance technology as the water content of the body increases. Also the use of leg length did not improve the accuracy of the prediction equation.

CONCLUSIONS

At the population level predictions of total body water obtained from foot-to-foot impedance technology compare well with measured total body water. However the significant correlation between the difference between predicted and measured total body water and the absolute value for total body water is a concern especially if the technology is used for body composition assessment during a weight loss program.

Selective activation of adenosine A3 receptors with N6-(3-chlorobenzyl)-5'-N-methylcarboxamidoadenosine (CB-MECA) provides cardioprotection via KATP channel activation

OBJECTIVE

The aim of this study was to characterize the adenosine A3 receptor agonist, N6-(3-chlorobenzyl)-5'-N-methylcarboxamidoadenosine (CB-MECA), evaluate its ability to reduce myocardial ischemia/reperfusion injury and determine the role of KATP-channel activation in A3 receptor-mediated cardioprotection.

METHODS

Binding affinities and adenylate cyclase inhibition were examined in CHO cells expressing rabbit recombinant adenosine A1 or A3 receptors. Infarct size (normalized for area-at-risk; % IA/AAR) was measured in buffer-perfused rabbit hearts exposed to 30-min regional ischemia and 120 min of reperfusion.

RESULTS

CB-MECA was 100-fold selective for A3 vs. A1 receptors (A3 Ki: 1 nM; A1 Ki: 105 nM). Five-min perfusion with CB-MECA before ischemia/reperfusion elicited a concentration-dependent reduction in infarct size (EC50: 0.3 nM). The CB-MECA-dependent cardioprotection (control: 58 +/- 2; CB-MECA: 21 +/- 3% IA/AAR) was unchanged by an A1-selective concentration of the antagonist, BWA1433, but was completely prevented (P < 0.05) by a nonselective (A1/A3) concentration (55 +/- 6% IA/AAR). The KATP channel inhibitors, glibenclamide and 5-HD, had no effect on control infarct size, yet significantly (P < 0.05) blunted the CB-MECA-dependent cardioprotection (glibenclamide: 49 +/- 6; 5-HD: 58 +/- 4% IA/AAR).

CONCLUSIONS

CB-MECA is a novel 100-fold A3 receptor-selective agonist which should prove useful for elucidating A3-dependent mechanisms in the rabbit heart. Selective stimulation of adenosine A3 receptors with CB-MECA reduces myocardial ischemia/reperfusion injury via a mechanism which involves activation of KATP channels.

Electroencephalographic and psychometric differences between boys with and without attention-deficit/Hyperactivity disorder (ADHD): a pilot study

Attention-Deficit/Hyperactivity Disorder (ADHD) is reported to have an incidence of 3-5%, and is associated with a variety of interpersonal, academic, and social problem behaviors. There is controversy as to whether ADHD is a learned behavioral or brain dysfunction. Research has explored a variety of measures to assess behavioral and brain dysfunctions in this population, with no consistent and clearly diagnostic results. We investigated whether a new psychometric and a new electroencephalographic procedure would clearly differentiate ADHD. The psychometric was based on DSM-IV criteria and the EEG measure was based on the assumption that ADHD interferes with cognitive transition from one discrete task to another. Parents of four ADHD boys (ages 8-12) and four age- and interest-matched non-ADHD boys completed the ADHD Symptom Inventory, while their sons' EEG was monitored during viewing of a video and reading of a book. For the ADHD boys, this was repeated a second time, 3 months later, to assess test-retest reliability. Both the psychometric and the EEG measures clearly differentiated the two samples (p's < .01) with no overlap in scores, were reliable over 3 months (r = .87), and were significantly correlated with one another (r = .85). While a small sample size, these robust, related and reliable findings suggest that both the psychometric and the psychophysiological EEG measures deserve further replication and exploration.

Relative sedimentation of hematopoietic progenitors in human cord blood, peripheral blood, and bone marrow as determined by counterflow centrifugal elutriation

BACKGROUND

The current use of cord blood (CB) and peripheral blood (PB) stem cells as alternatives or adjunctives to bone marrow (BM) for hematopoietic reconstitution in the treatment of various diseases prompted an examination of the progenitors of these tissues by counterflow centrifugal elutriation (CCE).

METHODS

The cells, obtained from normal donors not primed with colony-stimulating factors, were centrifuged at 3000 rpm in a Beckman Sanderson Chamber. Fractions (Frs.) were collected at (1) 18 ml/min, (2) 25 ml/min, (3) 32 ml/min, (4) 40 ml/min, and (5) the rotor-off fraction.

RESULTS

Clonogenic assays revealed differences in the fraction localizations for CB and PB when compared to BM, i.e., recovery of the colony-forming units for CB and PB was greater in the small-medium cell size CCE fractions, and those from BM were found primarily among the medium-large cell size fractions. Thus, although colony-forming unit granulocyte/macrophage colonies were distributed throughout Frs. 2-5 of BM, CB and PB showed 80% of the total to be in Frs. 2 and 3. Further, although burst-forming unit erythroid colonies of BM were distributed equally in Frs. 2 and 3, greater than 70% of the total burst-forming unit erythroid colonies in CB and PB were found in Fr. 2. Distribution of the CD34 cells in the fractions correlated with the colony-forming units in that these were found primarily in Frs. 2 and 3 of CB and PB, whereas they were present in significant numbers throughout Frs. 1-5 of BM.

CONCLUSIONS

We interpret these findings to indicate CB and PB to be qualitatively similar in their hematopoietic lineage development and to contain a greater proportion of early versus late progenitors relative to those found in BM.

Expression of the rat adrenomedullin receptor or a putative human adrenomedullin receptor does not correlate with adrenomedullin binding or functional response

There has been considerable difficulty in defining distinct adrenomedullin (AM) binding sites and function in vivo. However, a rat adrenomedullin receptor (rAMR) and a putative human adrenomedullin receptor (hAMR) have recently been reported. We attempted to confirm and extend the pharmacological characterization of these cloned receptors. COS-7 cells transfected with rAMR or epitope tagged rAMR display abundant rAMR mRNA expression and cell-surface receptor localization. Specific 125I-AM binding is detected in transfected cells; however, similar levels of binding are also detected in cells transfected with vector DNA alone. This AM binding site fails to mediate any changes in cAMP in response to AM. In contrast, Swiss 3T3 cells, expressing specific endogenous AM receptors, display AM binding and functional cAMP responses. Transfection studies performed with the putative hAMR yield similar results. These data suggest that the proposed rAMR and hAMR do not represent authentic adrenomedullin receptors.

Relative importance of adenosine A1 and A3 receptors in mediating physiological or pharmacological protection from ischemic myocardial injury in the rabbit heart

Although ischemic preconditioning (IP) in several species can be pharmacologically mimicked by selective adenosine A1 or A3 receptor agonists, it is currently unclear which receptor subtype (A1 and/or A3) is physiologically involved in mediating IP. To investigate this question, we determined (a) the affinity of adenosine for rabbit adenosine A1 and A3 receptors, and (b) the effects of selective rabbit A1 receptor blockade on IP and adenosine-mediated cardioprotection in a rabbit Langendorff model of myocardial ischemia-reperfusion injury. Adenosine was 19-fold selective for inhibition of N6-(4-amino-3-[125I]iodobenzyl)adenosine (125I-ABA) binding to recombinant rabbit A1 v rabbit A3 receptors (A1 Ki: 28 nm; A3 Ki 532 nm). Buffer-perfused rabbit hearts were exposed to 30 min regional ischemia and 120 min of reperfusion, and infarct size was measured by tetrazolium staining and normalized for area-at-risk (IA/AAR). Ischemic preconditioning (5 min global ischemia and 10 min reperfusion) or adenosine (20 micro M, 5 min) perfusion reduced infarct size (IA/AAR) to 17+/-3 and 14+/-2%, respectively (controls: 59+/-2%). Ischemic preconditioning and adenosine-mediated cardioprotection were completely blocked (57+/-2 and 61+/-4% IA/AAR, respectively) in the presence of a rabbit A1-selective concentration (50 nm) of the antagonist BWA1433 (rabbit A1 Ki: 3 nm; A3 Ki; 746 n m). Thus, whereas recent studies have demonstrated that selective A1 or A3 receptor agonists can both pharmacologically mimic IP, the results of the present study suggest that the adenosine-mediated component of IP in the isolated rabbit heart is preferentially mediated by adenosine A1 receptors, potentially due to adenosine's selectivity for this receptor subtype.

POP-1 and anterior-posterior fate decisions in C. elegans embryos

Blastomeres in C. elegans embryos execute lineage programs wherein the fate of a cell is correlated reproducibly with the division sequence by which that cell is born. We provide evidence that the pop-1 gene functions to link anterior-posterior cell divisions with cell fate decisions. Each anterior cell resulting from an anterior-posterior division appears to have a higher level of nuclear POP-1 protein than does its posterior sister. Genes in the C. elegans Wnt pathway are required for this inequality in POP-1 levels. We show that loss of pop-1(+) activity leads to several types of anterior cells adopting the fates of their posterior sisters. These results suggest a mechanism for the invariance of blastomere lineages.

end-1 encodes an apparent GATA factor that specifies the endoderm precursor in Caenorhabditis elegans embryos

The endoderm in the nematode Caenorhabditis elegans is clonally derived from the E founder cell. We identified a single genomic region (the endoderm-determining region, or EDR) that is required for the production of the entire C. elegans endoderm. In embryos lacking the EDR, the E cell gives rise to ectoderm and mesoderm instead of endoderm and appears to adopt the fate of its cousin, the C founder cell. end-1, a gene from the EDR, restores endoderm production in EDR deficiency homozygotes. end-1 transcripts are first detectable specifically in the E cell, consistent with a direct role for end-1 in endoderm development. The END-1 protein is an apparent zinc finger-containing GATA transcription factor. As GATA factors have been implicated in endoderm development in other animals, our findings suggest that endoderm may be specified by molecularly conserved mechanisms in triploblastic animals. We propose that end-1, the first zygotic gene known to be involved in the specification of germ layer and founder cell identity in C. elegans, may link maternal genes that regulate the establishment of the endoderm to downstream genes responsible for endoderm differentiation.

Evidence for a role for both the adenosine A1 and A3 receptors in protection of isolated human atrial muscle against simulated ischaemia

OBJECTIVE

Adenosine receptor activation has been implicated in the mechanism of ischaemic preconditioning protection. Evidence suggests adenosine A1 receptor involvement, and possibly A3 receptor involvement in the rabbit. This study investigated the roles of these receptors in human preconditioning. Human A1- and A3-selective compounds were chosen based on Ki values for inhibition of N6-(4-amino-3-[125I]iodobenzyl)adenosine (125I-ABA) binding to stably expressed recombinant human A1 and A3 receptors. Cyclopentyladenosine (CPA), a 194-fold selective A1 agonist, and iodobenzylmethylcarboxamidoadenosine (IBMECA), a 10-fold selective A3 agonist were used alone and in combination with dipropylcyclopentylxanthine (DPCPX) a 62-fold selective A1 antagonist.

METHODS

Human atrial trabeculae were superfused with oxygenated Tyrode's solution. After stabilisation, muscles underwent one of 8 protocols (n = 6 per group), followed by 90 min of simulated ischaemia and 120 min of reoxygenation. The experimental endpoint was recovery of contractile function, presented as percentage baseline function.

RESULTS

5 nM CPA (52.2 +/- 3.1%), 30 nM IBMECA (49.7 +/- 3.8%) and preconditioning (55.3 +/- 2.5%) produced similar functional recoveries at 120 min of reoxygenation; significantly different to controls (27.7 +/- 1.0%; P < 0.05, ANOVA). When DPCPX (200 nM) was added prior to 5 nM CPA, protection was lost (31.8 +/- 0.9%), but when added prior to 30 nM IBMECA, muscles continued to be significantly protected (41.5 +/- 2.3%).

CONCLUSIONS

In human atrium both A1 and A3 receptor stimulation appears to mimic ischaemic preconditioning. This may represent the first evidence for A3 receptor involvement in 'pharmacological' preconditioning of human myocardium.

Cloning and characterization of LcEcR: a functional ecdysone receptor from the sheep blowfly Lucilia cuprina

Degenerate oligonucleotides were designed on the basis of conserved amino acid sequences in the DNA binding domains of the ecdysone receptors from Drosophila melanogaster (DmEcR) and Chironomus tentans (CtEcR). Using these oligonucleotides a fragment encoding part of the DNA binding domain of the Lucilia cuprina ecdysone receptor (LcEcR) was amplified by polymerase chain reaction (PCR) from genomic DNA and cloned. This cloned fragment was used to screen a cDNA library which was prepared from Lucilia larvae at the late third instar. A full-length LcEcR gene was isolated within a 3336 bp cDNA clone. The conceptually translated amino acid sequence of this open reading frame (757 amino acids) contained all five domains typical of a steroid hormone receptor. Alignment comparisons and phylogenetic analyses indicated that LcEcR most closely resembled the B1 isoform of DmEcR relative to other known insect steroid receptors, including six insect EcRs. An antisense RNA probe specific for the 3' end of LcEcR was used in ribonuclease protection assays to detect significant levels of LcEcR mRNA in embryos, late third instar larvae, pupae and adult females during Lucilia development. This pattern parallels the pattern of expression observed for DmEcR mRNAs during Drosophila development. The LcEcR gene was engineered for expression in mammalian cells, and we now report that the cloned LcEcR is functional and can act as an ecdysteroid-dependent transcription factor in mammalian cells.

Selective adenosine A3 receptor stimulation reduces ischemic myocardial injury in the rabbit heart

OBJECTIVE

The aim of this study was to determine whether selective activation of the adenosine A3 receptor reduces infarct size in a Langendorff model of myocardial ischemia-reperfusion injury.

METHODS

Buffer-perfused rabbit hearts were exposed to 30 min regional ischemia and 120 min of reperfusion. Infarct size was measured by tetrazolium staining and normalized for area-at-risk (IA/AAR).

RESULTS

Preconditioning by 5 min global ischemia and 10 min reperfusion reduced infarct size (IA/AAR) to 19 +/- 4% (controls: 67 +/- 5%). Replacing global ischemia with 5 min perfusion of the rabbit A3-selective agonist, IB-MECA (A3 Ki: 2 nM; A1 Ki: 30 nM) elicited a concentration-dependent reduction in infarct size; 50 nM IB-MECA reduced IA/AAR to 24 +/- 4%. The A1-selective agonist, R-PIA (25 nM) reduced IA/AAR to a similar extent (21 +/- 6%). However, while the cardioprotective effect of R-PIA was significantly inhibited (54 +/- 7% IA/AAR) by the rabbit A1-selective antagonist, BWA1433 (50 nM), the IB-MECA-dependent cardioprotection was unaffected (28 +/- 6% IA/AAR). A non-selective (A1 vs. A3) concentration of BWA1433 (5 microM) significantly attenuated the IB-MECA-dependent cardioprotection (61 +/- 7% IA/AAR).

CONCLUSIONS

These data clearly demonstrate that selective A3 receptor activation provides cardioprotection from ischemia-reperfusion injury in the rabbit heart. Furthermore, the degree of A3-dependent cardioprotection is similar to that provided by A1 receptor stimulation or ischemic preconditioning.

Cloning, expression and pharmacological characterization of rabbit adenosine A1 and A3 receptors

The role of adenosine A1 and A3 receptors in mediating cardioprotection has been studied predominantly in rabbits, yet the pharmacological characteristics of rabbit adenosine A1 and A3 receptor subtypes are unknown. Thus, the rabbit adenosine A3 receptor was cloned and expressed, and its pharmacology was compared with that of cloned adenosine A1 receptors. Stable transfection of rabbit A1 or A3 cDNAs in Chinese hamster ovary-K1 cells resulted in high levels of expression of each of the receptors, as demonstrated by high-affinity binding of the A1/A3 adenosine receptor agonist N6-(4-amino-3-[125I]iodobenzyl)adenosine (125I-ABA). For both receptors, binding of 125I-ABA was inhibited by the GTP analog 5'-guanylimidodiphosphate, and forskolin-stimulated cyclic AMP accumulation was inhibited by the adenosine receptor agonist (R)-phenylisopropyladenosine. The rank orders of potency of adenosine receptor agonists for inhibition of 125I-ABA binding were as follows: rabbit A1, N6-cyclopentyladenosine = (R)-phenylisopropyladenosine > N-ethylcarboxamidoadenosine > or = I-ABA > or = N6-2-(4-aminophenyl) ethyladenosine > > N6-(3-iodobenzyl)adenosine-5'-N-methyluronamide > N6-(4-amino-3-benzyl)adenosine; rabbit A3, N6-(3-iodobenzyl)adenosine-5'-N-methyluronamide > or = I-ABA > > N-ethylcarboxamidoadenosine > N6-2-(4-aminophenyl) ethyladenosine = N6-cyclopentyladenosine = (R)-phenylisopropyladenosine > N6-(4-amino-3-benzyl)adenosine. The adenosine receptor antagonist rank orders were as follow: rabbit A1, 8-cyclopentyl-1,3-dipropylxanthine > 1,3- dipropyl-8-(4-acrylate)phenylxanthine > or = xanthine amine congener > > 8-(p-sulfophenyl)theophylline; rabbit A3, xanthine amine congener > 1,3-dipropyl-8-(4-acrylate)phenylxanthine > or = 8-cyclopentyl-1,3-dipropylxanthine > > 8-(p-sulfophenyl)theophylline. These observations confirm the identity of the expressed proteins as A1 and A3 receptors. The results will facilitate further in-depth studies of the roles of A1 and A3 receptors in adenosine-mediated cardioprotection in rabbits, which can now be based on the appropriate recombinant rabbit A1 and A3 receptor pharmacology.

Differentiation induced by the c-Mpl cytokine receptor is blocked by mutant Shc adaptor protein

c-Mpl, a member of the cytokine receptor superfamily, induces both proliferative and differentiation responses when stimulated with its ligand thrombopoietin (TPO). To examine signal transduction pathways associated with differentiation versus proliferation, 32D clone 3 cells, a murine interleukin 3-(IL-3)-dependent cell line capable of granulocytic differentiation, were engineered to express human c-Mpl (designated 32DM.2). Human TPO-containing medium was produced by transient transfection of 293 cells. Treatment of 32DM.2 cells with human TPO induced cellular aggregates within 12 h of exposure to ligand. 32DM.2 cells maintained in the presence of TPO did not change in cell number over a 72-h period and acquired characteristics of granulocytic differentiation as evidenced by metamyelocytic cellular morphology. The differentiation effect of TPO was observed in the absence and presence of the mitogen IL-3. Evaluation of protein tyrosine phosphorylation following exposure to ligand revealed that TPO stimulation induced an elevated level of tyrosine phosphorylation of the adaptor protein Shc when compared with IL-3. However, treatment of 32DM.2 cells with TPO did not result in the phosphorylation of mitogen-activated protein kinase (MAPK). To evaluate the potential role of Shc in c-Mpl differentiation, we transfected 32DM.2 cells with a mutant Shc gene that lacked the region coding for the phosphotyrosine interaction domain (delta PI-Shc). Expression of the delta PI-Shc protein in 32DM.2 cells blocked the TPO differentiation response with no effect on IL-3-stimulated proliferation. These studies demonstrate that c-Mpl-induced differentiation results from the activation of signal transduction pathways that are dominant to the IL-3 proliferative response and independent of the Ras/MAPK signal transduction pathway. The ability of the delta PI-Shc protein to block TPO-induced differentiation implicates Shc as a mediator of signal transduction pathways leading to differentiation, which is distinct from its role as a mediator in activating the Ras/MAPK pathway.

Onset of strong scintillation with application to remote sensing of turbulence inner scale

Numerical simulation of propagation through atmospheric turbulence of an initially spherical wave is used to calculate irradiance variance σ(2)(I), variance of log irradiance σ(2)(ln I), and mean of log irradiance ?In I? for 13 values of l(0)/R(f) (i.e., of turbulence inner scale l(0) normalized by Fresnel scale R(F)) and 10 values of Rytov variance σ(2)(Rytov), which is the irradiance variance, including the inner-scale effect, predicted by perturbation methods; l(0)/R(f) was varied from 0 to 2.5 and σ(2)(Rytov) from 0.06 to 5.0. The irradiance probability distribution function (PDF) and, hence, σ(2)(I), σ(2)(In I), and ?ln I? are shown to depend on only two dimensionless parameters, such as l(o)/R(F) and σ(2)(Rytov). Thus the effects of the onset of strong scintillation on the three statistics are characterized completely. Excellent agreement is obtained with previous simulations that calculated σ(2)(I). We find that σ(2)(I), σ(2)(In I), and ?ln I? are larger than their weak-scintillation asymptotes (namely, σ(2)(Rytov), σ(2)(Rytov), and - σ(2)(Rytov)/2, respectively) for the onset of strong scintillation for all l(0)/R(f). An exception is that for the largest l(0)/R(f), the onset of strong scintillation causes σ(2)(ln I) to decrease relative to its weak-scintillation limit, σ(2)(Rytov). We determine the efficacy of each of the three statistics for measurement of l(0), taking into account the relative difficulties of measuring each statistic. We find that measuring σ(2)(I) is most advantageous, although it is not the most sensitive to l(0) of the three statistics. All three statistics and, hence, the PDF become insensitive to l(0) for roughly 1 < β0(2) < 3 (where β0(2) is σ (2)(Rytov) for l(0) = 0); this is a condition for which retrieval of l(0) is problematic.

Different levels of the C. elegans growth factor LIN-3 promote distinct vulval precursor fates

An invariant spatial pattern of three cell fates (3 degrees-3 degrees-2 degrees-1 degree-2 degrees-3 degrees) is generated from a field of multipotent precursor cells during C. elegans vulval development. We demonstrate that the epidermal growth factor-like domain of the LIN-3 protein can induce either of two distinct vulval cell fates: a high dose of LIN-3 induces a 1 degree fate; a lower dose of LIN-3 induces a 2 degrees fate. A high dose of LIN-3 can also induce adjacent vulval precursor cells to assume 1 degree fates; thus, high levels of LIN-3 can override the lateral signaling that normally inhibits formation of adjacent 1 degree fates. We propose that the invariant pattern of vulval cell fates is generated by a graded distribution of LIN-3 that promotes different vulval fates according to local concentration and by a lateral signal that reinforces this initial bias.

WIN 17317-3: novel nonpeptide antagonist of voltage-activated K+ channels in human T lymphocytes

We report the in vitro biological characterization of WIN 17317-3 (1-benzyl-7-chloro-4-n-propylimino-1,4-dihydroquinoline hydrochloride), a novel inhibitor of voltage-activated (n-type) K+ channels in human T lymphocytes. WIN 17317-3 inhibits 125I-charybdotoxin binding to n-type K+ channels with an IC50 value of 83 +/- 4 nM. WIN 17317-3 demonstrates competitive inhibition of 125I-charybdotoxin binding by increasing its dissociation constant without changing the total number of channels bound and by having no effect on its dissociation rate constant. WIN 17317-3 inhibits whole-cell, n-type K+ currents with characteristics indicative of open channel block and has an IC50 value of 335 nM. The compound is 150-fold selective for n-type K+ channels, compared with Ca(2+)-activated, charybdotoxin-sensitive K+ channels in smooth muscle. In purified CD4+ T lymphocytes activated with either anti-CD3 plus phorbol ester or anti-CD3 plus anti-CD28, WIN 17317-3 decreases interleukin-2 production with EC50 values of 0.8 microM and 1 microM, respectively. WIN 17317-3 is a novel, potent, and selective nonpeptide n-type K+ channel antagonist that inhibits interleukin-2 production in human T lymphocytes.

Transfer of a functional arabinose operator-repressor system to Drosophila melanogaster Schneider line-2 cells

Regulatory elements from the arabinose operon of Escherichia coli were transfected into Drosophila melanogaster Schneider line 2 cells to test their ability to function in animal cells. A construct containing an araC fusion gene (encoding AraC protein) under the control of an act5C (encoding actin) promoter and a construct containing a lacZ fusion gene (reporter gene) also under the control of an act5C promoter were used to build a regulatory circuit in the D. melanogaster cells. We have demonstrated that a AraC fusion protein can be synthesised in Schneider cells where it is able to repress the transcription of the reporter gene containing AraC-binding sites inserted between the transcription start point and the initiation codon. The reporter gene activity can be further modulated by the addition of arabinose to the medium.

The uptake of the third oral vitamin K dose in general practice

AIM

To assess the uptake of the third oral vitamin K dose in general practice.

METHOD

Infants born between 1 October 1992 and 4 February 1993 in the Rotorua area were identified. This included all infants born at the maternity unit and home births within the Rotorua area. The general practitioner recorded as the preferred primary healthcare provider was contacted and a questionnaire completed.

RESULTS

There were 521 recorded births. Of these 104 were excluded as they were non resident within the Rotorua area. Of those infants residing in Rotorua after birth (417), a further 77 were excluded due to: No general practitioner identified 3; deaths 3; transfers--outcome unknown 18; and intramuscular vitamin K given at birth 53, giving a survey population of 340. Forty general practitioners were identified as the preferred primary health care provider. There was a 100% questionnaire response rate. In the survey population the uptake of the third dose of vitamin K was 90.6%. (308 out of 340).

CONCLUSIONS

Further investigation is required to identify those infants not receiving the third oral dose and why. A more specific questionnaire requesting information as to why the third dose was omitted should have been designed. It may be necessary to consider the use of a single intramuscular dose of vitamin K to those breastfed infants who can be considered to have a high probability of not receiving the three oral doses of vitamin K within the first six weeks of life regardless of other risk factors.

Class I antiarrhythmic drugs: allosteric inhibitors of [3H] batrachotoxinin binding to rat cardiac sodium channels

This study assessed whether class I antiarrhythmic drugs allosterically inhibit [3H]batrachotoxinin A 20-alpha-benzoate ([3H]BTXB) binding to sodium channels on freshly isolated rat cardiac myocytes. All class I drugs tested inhibited equilibrium [3H]BTXB binding in a concentration-dependent manner. Scatchard analysis showed that disopyramide, flecainide, transcainide, lidocaine and amiodarone reduced [3H]BTXB maximum binding (Bmax) whereas procainamide, mexiletine, quinidine, quinine, tocainide, propafenone, encainide and O-demethylencainide increased [3H]BTXB KD but had little effect on Bmax. Kinetic [3H]BTXB binding assays were used to assess the mechanism by which class I drugs inhibit [3H]BTXB binding. Drugs that increase the unidirectional dissociation rate constant (k-1) of [3H]BTXB probably bind to sodium channels to which [3H]BTXB is already bound. Although all class I drugs increased the k-1 of [3H]BTXB, they did so weakly and at concentrations above the IC50 values of the drugs. Thus, drug binding to [3H]BTXB-bound channels does not appear to be the predominant mechanism underlying their ability to inhibit [3H]BTXB binding. Conversely, drugs which allosterically decrease the unidirectional association rate constant (K+1) of [3H]BTXB probably bind to channels to which [3H]BTXB is not already bound. All class I drugs decreased the k+1 of [3H]BTXB, indicating drug binding to [3H]BTXB-free channels. The estimated affinities of drugs for [3H]BTXB-free channels correlated closely with the IC50 values of these drugs (r = 0.94, P < .001), suggesting that this effect is a common and major determinant in their ability to inhibit [3H]BTXB binding. The results are discussed in light of electrophysiologic theories of class I antiarrhythmic drug action.