Comparisons between bone and cementum compositions and the possible basis for their layered appearances

In humans, age estimation from the adult skeleton represents an attempt to determine chronological age based on growth and maturational events. In teeth, such events can be characterized by appositional growth layers in midroot cementum. The purpose of this study was to determine the underlying cause of the layered microstructure of human midroot cementum. Whether cementum growth layers are caused by changes in relative mineralization, collagen packing and/or orientation, or by variations in organic matrix apposition was investigated by subjecting midroot sections of human canine teeth to analysis using polarized light and scanning electron microscopy (SEM). Polarized light was used to examine transverse midroot sections in both mineralized and demineralized states. Mineralized sections were also reexamined following subsequent decollagenization. Polarized light was additionally used in the examination of mineralized sections taken transversely, longitudinally, and obliquely from the same tooth root. From the birefringence patterns it was concluded that collagen orientation does not change with varying section plane. Instead, the mineral phase was most responsible for the birefringence of the cementum. SEM studies suggested that neither collagen packing nor collagen orientation change across the width of the cementum, confirming and validating the results of the polarized light examination. Also, SEM analysis using electron backscatter and the electron probe suggested no changes in the mean atomic number density, calcium, phosphate, and sulfur levels across the width of the cementum. Therefore, we conclude that crystalline orientation and/or size is responsible for the layered appearance of cementum. (Bone 30:386-392; 2002) (C) 2002 by Elsevier Science Inc. All rights reserved.

Slowed conduction and ventricular tachycardia after targeted disruption of the cardiac sodium channel gene Scn5a

Voltage-gated sodium channels drive the initial depolarization phase of the cardiac action potential and therefore critically determine conduction of excitation through the heart. In patients, deletions or loss-of-function mutations of the cardiac sodium channel gene, SCN5A, have been associated with a wide range of arrhythmias including bradycardia (heart rate slowing), atrioventricular conduction delay, and ventricular fibrillation. The pathophysiological basis of these clinical conditions is unresolved. Here we show that disruption of the mouse cardiac sodium channel gene, Scn5a, causes intrauterine lethality in homozygotes with severe defects in ventricular morphogenesis whereas heterozygotes show normal survival. Whole-cell patch clamp analyses of isolated ventricular myocytes from adult Scn5a(+/-) mice demonstrate a approximate to50% reduction in sodium conductance. Scn5a(+/-) hearts have several defects including impaired atrioventricular conduction, delayed intramyocardial conduction, increased ventricular refractoriness, and ventricular tachycardia with characteristics of reentrant excitation. These findings reconcile reduced activity of the cardiac sodium channel leading to slowed conduction with several apparently diverse clinical phenotypes, providing a model for the detailed analysis of the pathophysiology of arrhythmias.

The intuitive basis of implicature: relevance theoretic implicitness versus gricean implying

The notion of implicature was first introduced by Paul Grice (1967, 1989), who defined it essentially as what is communicated less what is said. This definition contributed in part to the proliferation of a large number of different species of implicature by neo-Griceans. Relevance theorists have responded to this by proposing a shift back to the distinction between "explicit" & "implicit" meaning (corresponding to "explicature" & "implicature," respectively). However, they appear to have pared down the concept of implicature too much, ignoring phenomena that may be better treated as implicatures in their overgeneralization of the concept of explicature. These problems have their roots in the fact that explicit & implicit meaning intuitively overlap & thus do not provide a suitable basis for distinguishing implicature from other types of pragmatic phenomena. An alternative conceptualization of implicature based on the concept of "implying" with which Grice originally associated his notion of implicature is thus proposed. From this definition, it emerges that implicature constitutes something else inferred by the addressee that is not literally said by the speaker. Instead, it is meant in addition to what the speaker literally says & is consequently defeasible like all other types of pragmatic phenomena. 1 Figure, 60 References. Adapted from the source document

Osteonectin/SPARC induction by ectopic beta(3) integrin in human radial growth phase primary melanoma cells

Expression of the beta(3) integrin subunit in melanoma in situ has been found to correlate with tumor thickness, the ability to invade and metastasize, and poor prognosis. Transition from the radial growth phase (RGP) to the vertical growth phase (VGP) is a critical step in melanoma progression and survival and is distinguished by the expression of beta(3), integrin. The molecular pathways that operate in melanoma cells associated with invasion and metastasis were examined by ectopic induction of the beta(3), integrin subunit in RGP SBcl2 and WM1552C melanoma cells, which converts these cells to a VGP phenotype. We used cDNA representational difference analysis subtractive hybridization between beta(3)-Positive and -negative melanoma cells to assess gene expression profile changes accompanying RGP to VGP transition. Fourteen fragments from known genes including osteonectin (also known as SPARC and BM-40) were identified after three rounds of representational difference analysis. Induction of osteonectin was confirmed by Northern and Western blot analysis and immunohistochemistry and correlated in organotypic cultures with the beta(3)-induced progression from RGP to VGP melanoma. Expression of osteonectin was also associated with reduced adhesion to vitronectin, but not to fibronectin. Osteonectin expression was not blocked when melanoma cells were cultured with anti-alpha(v)beta(3) LM609 mAb, mitogen-activated protein kinase, or protein kinase C inhibitors, indicating that other signaling pathway(s) operate through a(v)beta(3) integrin during conversion from RGP to VGP.

The role of conserved CXXXRXG motif in the expression and function of the human norepinephrine transporter

Highly conserved motifs in the monoamine transporters, e.g. the human norepinephrine transporter (hNET) GXXXRXG motif which was the focus of the present study, are likely to be important structural features in determining function. This motif was investigated by mutating the glycines to glutamate (causing loss of function) and alanine, and the arginine to glycine. The effects of hG117A, hR121G and hG123A mutations on function were examined in COS-7 cells and compared to hNET. Substrate K-m values were decreased for hG117A and hG123A, and their K values for inhibition of [3 H]nisoxetine binding were decreased 3-4-fold and 4-6-fold, respectively. Transporter turnover was reduced to 65% of hNET for hG117A and hR121G and to 28% for hG123A, suggesting that substrate translocation is impaired. K values of nisoxetine and desipramine for inhibition of [H-3]norepinephrine uptake were increased by 5-fold for hG117A, with no change for cocaine. The K-i value of cocaine was increased by 3-fold for hG123A, with no change for nisoxetine and desipramine. However, there were no effects of the mutations on the K-d of [H-3]nisoxetine binding or K-i values of desipramine or cocaine for inhibition of [H-3]nisoxetine binding. Hence, glycine residues of the GXXXRXG motif are important determinants of NET expression and function, while the arginine residue does not have a major role. This study also showed that antidepressants and psychostimulants have different NET binding sites and provided the first evidence that different sites on the NET are involved in the binding of inhibitors and their competitive inhibition of substrate uptake. (C) 2002 Elsevier Science B.V. All rights reserved.

Evaluation of line-transect sampling for estimating koala abundance in the Pine Rivers Shire, south-east Queensland

Distance sampling using line transects has not been previously used or tested for estimating koala abundance. In July 2001, a pilot survey was conducted to compare the use of line transects with strip transects for estimating koala abundance. Both methods provided a similar estimate of density. On the basis of the results of the pilot survey, the distribution and abundance of koalas in the Pine Rivers Shire, south-east Queensland, was determined using line-transect sampling. In total, 134 lines (length 64 km) were used to sample bushland areas. Eighty-two independent koalas were sighted. Analysis of the frequency distribution of sighting distances using the software program DISTANCE enabled a global detection function to be estimated for survey sites in bushland areas across the Shire. Abundance in urban parts of the Shire was estimated from densities obtained from total counts at eight urban sites that ranged from 26 to 51 ha in size. Koala abundance in the Pine Rivers Shire was estimated at 4584 (95% confidence interval, 4040-5247). Line-transect sampling is a useful method for estimating koala abundance provided experienced koala observers are used when conducting surveys.

Morphology, ultrastructure, and implied function of ciliated sensory structures on the developmental stages of Merizocotyle icopae (Monogenea : Monocotylidae)

Experimental infections were used to track the fate of the dorsal sensilla of Merizocotyle icopae (Monogenea: Monocotylidae) from nasal tissue of the shovelnose ray, Rhinobatos typus (Rhinobatidae). Scanning and transmission electron microscopy revealed that 3 types of uniciliate dorsal sensilla exist at different times in the development of the monogenean. Type 1 sensilla have little or no invagination where the cilium exits the distal end of the dendrite and possess a ring of epidermis surrounding the cilium distal to the invagination. Type 2 sensilla have a deep invagination where the cilium exits the dendrite. Type 3 sensilla can be distinguished from the other types by the shape of the dendrite. The larvae have predominantly Type I dorsal sensilla, most of which are lost approximately 24 h after infection and a few Type 2 sensilla, which are retained. Additional Type 2 sensilla (termed Adult Type 2 sensilla), which are slightly different morphologically from the Type 2 sensilla of the larvae, form in later stages of development. Numerous Type 3 sensilla are unique to the dorsal surface of adults. Loss of all Type I sensilla upon attachment to the host, R. typus, suggests that these may be chemo- or mechanoreceptors responsible for host location by the swimming infective larvae. Type 2 sensilla appear to be important in the larvae, juveniles, and adults whereas the modality mediated by Type 3 is specific to adults. (C) 2003 Wiley-Liss, Inc.

Slurry flow in mills: grate-pulp lifter discharge systems (Part 2)

Pulp lifters, also known, as pan lifters are an integral part of the majority of autogenous (AG), semi-autogenous (SAG) and grate discharge ball mills. The performance of the pulp lifters in conjunction with grate design determines the ultimate flow capacity of these mills. Although the function of the pulp lifters is simply to transport the slurry passed through the discharge grate into the discharge trunnion, their performance depends on their design as well as that of the grate and operating conditions such as mill speed and charge level. However, little or no work has been reported on the performance of grate-pulp lifter assemblies and in particular the influence of pulp lifter design on slurry transport. Ideally, the discharge rate through a grate-pulp lifter assembly should be equal to the discharge rate through at a given mill hold-up. However, the results obtained have shown that conventional pulp lifter designs cause considerable restrictions to flow resulting in reduced flow capacity. In this second of a two-part series of papers the performance of conventional pulp lifters (radial and spiral designs) is described and is based on extensive test work carried out in a I m diameter pilot SAG mill. (C) 2003 Elsevier Science Ltd. All rights reserved.

Identification of residues and domains of Raf important for function in vivo and in vitro

Random mutagenesis and genetic screens for impaired Raf function in Caenorhabditis elegans were used to identify six loss-of-function alleles of lin-45 raf that result in a substitution of a single amino acid. The mutations were classified as weak, intermediate, and strong based on phenotypic severity. We engineered these mutations into the homologous residues of vertebrate Raf-1 and analyzed the mutant proteins for their underlying biochemical defects. Surprisingly, phenotype strength did not correlate with the catalytic activity of the mutant proteins. Amino acid substitutions Val-589 and Ser-619 severely compromised Raf kinase activity, yet these mutants displayed weak phenotypes in the genetic screen. Interestingly, this is because these mutant Raf proteins efficiently activate the MAPK (mitogen-activated protein kinase) cascade in living cells, a result that may inform the analysis of knockout mice. Equally intriguing was the observation that mutant proteins with non-functional Ras-binding domains, and thereby deficient in Ras-mediated membrane recruitment, displayed only intermediate strength phenotypes. This confirms that secondary mechanisms exist to couple Ras to Raf in vivo. The strongest phenotype in the genetic screens was displayed by a S508N mutation that again did not correlate with a significant loss of kinase activity or membrane recruitment by oncogenic Ras in biochemical assays. Ser-508 lies within the Raf-1 activation loop, and mutation of this residue in Raf-1 and the equivalent Ser-615 in B-Raf revealed that this residue regulates Raf binding to MEK. Further characterization revealed that in response to activation by epidermal growth factor, the Raf-S508N mutant protein displayed both reduced catalytic activity and aberrant activation kinetics: characteristics that may explain the C. elegans phenotype.

T cell regulation of the immune response to infection in periodontal diseases

Although T cells have been implicated in the pathogenesis and are considered to be central both in progression and control of the chronic inflammatory periodontal diseases, the precise contribution of T cells to the regulation of tissue destruction has not been fully elucidated. Current dogma suggests that immunity to infection is controlled by distinct T helper 1 (Th1) and T helper 2 (Th2) subsets of T cells classified on the basis of their cytokine profile. Further, a subset of T cells with immunosuppressive function and cytokine profile distinct from Th1 or Th2 has been described and designated as regulatory T cells. Although these regulatory T cells have been considered to maintain self-tolerance resulting in the suppression of auto-immune responses, recent data suggest that these cells may also play a role in preventing infection-induced immunopathology. In this review, the role of functional and regulatory T cells in chronic inflammatory periodontal diseases will be summarized. This should not only provide an insight into the relationship between the immune response to periodontopathic bacteria and disease but should also highlight areas of development for potentially new therapeutic modalities.

Impulse-response function of splanchnic circulation with model-independent constraints: theory and experimental validation

Modeling physiological processes using tracer kinetic methods requires knowledge of the time course of the tracer concentration in blood supplying the organ. For liver studies, however, inaccessibility of the portal vein makes direct measurement of the hepatic dual-input function impossible in humans. We want to develop a method to predict the portal venous time-activity curve from measurements of an arterial time-activity curve. An impulse-response function based on a continuous distribution of washout constants is developed and validated for the gut. Experiments with simultaneous blood sampling in aorta and portal vein were made in 13 anesthetized pigs following inhalation of intravascular [O-15] CO or injections of diffusible 3-O[ C-11] methylglucose (MG). The parameters of the impulse-response function have a physiological interpretation in terms of the distribution of washout constants and are mathematically equivalent to the mean transit time ( T) and standard deviation of transit times. The results include estimates of mean transit times from the aorta to the portal vein in pigs: (T) over bar = 0.35 +/- 0.05 min for CO and 1.7 +/- 0.1 min for MG. The prediction of the portal venous time-activity curve benefits from constraining the regression fits by parameters estimated independently. This is strong evidence for the physiological relevance of the impulse-response function, which includes asymptotically, and thereby justifies kinetically, a useful and simple power law. Similarity between our parameter estimates in pigs and parameter estimates in normal humans suggests that the proposed model can be adapted for use in humans.