Ocupación del microhábitat y morfología funcional de cuatro especies de lagartos agámidos simpátridas del desierto de Kyzylkum, en Uzbekistán central

We examined microhabitat occupation and functional morphology of four sympatric agamid lizards(Phrynocephalus helioscopus helioscopus, P. interscapularis, P. mystaceus galli and Trapelus sanguinolentus) at three sites in the arid zone of central Uzbekistan. At two sites located in sand dunes, substrate attributes played a key role in habitat selection by three syntopic species. At a third flat, stony site, P. helioscopus selected habitat non-randomly, tending to occur close to sparse, low vegetation. Syntopic taxa were separated in morphospace, and there was a trend for taxa with proportionally longer limbs to have faster field escape speeds. Field escape distances and predator avoidance tactics differed between species, with two main escape strategies (crypsis or sand-diving following an escape sprint). We caution that broad–scale threatening processes such as over-grazing and salinity may be having a detrimental effect on microhabitat features important to terrestrial reptiles in Uzbekistan. Key words: Agamidae, Central Asia, Microhabitat occupation, Functional morphology.We examined microhabitat occupation and functional morphology of four sympatric agamid lizards(Phrynocephalus helioscopus helioscopus, P. interscapularis, P. mystaceus galli and Trapelus sanguinolentus) at three sites in the arid zone of central Uzbekistan. At two sites located in sand dunes, substrate attributes played a key role in habitat selection by three syntopic species. At a third flat, stony site, P. helioscopus selected habitat non-randomly, tending to occur close to sparse, low vegetation. Syntopic taxa were separated in morphospace, and there was a trend for taxa with proportionally longer limbs to have faster field escape speeds. Field escape distances and predator avoidance tactics differed between species, with two main escape strategies (crypsis or sand-diving following an escape sprint). We caution that broad–scale threatening processes such as over-grazing and salinity may be having a detrimental effect on microhabitat features important to terrestrial reptiles in Uzbekistan. Key words: Agamidae, Central Asia, Microhabitat occupation, Functional morphology.Examinamos la ocupación del microhábitat y la morfología funcional decuatro lagartos agámidos simpátridas (Phrynocephalus helioscopus helioscopus, P. interscapularis, P. mystaceus galli y Trapelus sanguinolentus) en tres localizaciones de la zona árida del Uzbekistán central. En dos localizaciones, situadas en una zona de dunas de arena, las características del sustrato tuvieron un papel clave en la selección del hábitat por parte de tres especies sintópicas. En una tercera zona, una llanura pedregosa, P. helioscopus no seleccionaba su hábitat al azar, con una clara tendencia a situarse cerca de vegetación baja y dispersa. Los taxa sintópicos estaban separados en el morfoespacio, y existía la tendencia entre los taxa con las extremidades proporcionalmente más largas a tener una mayor velocidad de huida. Las distancias de huida de campo y las tácticas de evitación de los depredadores diferían según las especies, con dos estrategias de huida principales (cripsis o enterramiento en la arena, seguidos de una carrera de escape). Hemos de advertir que los procesos amenazadores a gran escala, tales como el sobrepastoreo y la salinización pueden tener un efecto perjudicial sobre las características del microhábitat que son importantes para los reptiles terrestres de Uzbekistán. Palabras clave: Agamidae, Asia central, Ocupación del microhábitat, Morfología funcional

Influence of V5/6-His Tag on the Properties of Gap Junction Channels Composed of Connexin43, Connexin40 or Connexin45

HeLa cells expressing wild-type connexin43, connexin40 or connexin45 and connexins fused with a V5/6-His tag to the carboxyl terminus (CT) domain (Cx43-tag, Cx40-tag, Cx45-tag) were used to study connexin expression and the electrical properties of gap junction channels. Immunoblots and immunolabeling indicated that tagged connexins are synthesized and targeted to gap junctions in a similar manner to their wild-type counterparts. Voltage-clamp experiments on cell pairs revealed that tagged connexins form functional channels. Comparison of multichannel and single-channel conductances indicates that tagging reduces the number of operational channels, implying interference with hemichannel trafficking, docking and/or channel opening. Tagging provoked connexin-specific effects on multichannel and single-channel properties. The Cx43-tag was most affected and the Cx45-tag, least. The modifications included (1) Vj-sensitive gating of Ij (Vj, gap junction voltage; Ij, gap junction current), (2) contribution and (3) kinetics of Ij deactivation and (4) single-channel conductance. The first three reflect alterations of fast Vj gating. Hence, they may be caused by structural and/or electrical changes on the CT that interact with domains of the amino terminus and cytoplasmic loop. The fourth reflects alterations of the ion-conducting pathway. Conceivably, mutations at sites remote from the channel pore, e.g., 6-His-tagged CT, affect protein conformation and thus modify channel properties indirectly. Hence, V5/6-His tagging of connexins is a useful tool for expression studies in vivo. However, it should not be ignored that it introduces connexin-dependent changes in both expression level and electrophysiological properties

Mechanism of inhibition of connexin channels by the quinine derivative N-benzylquininium

The anti-malarial drug quinine and its quaternary derivative N-benzylquininium (BQ+) have been shown to inhibit gap junction (GJ) channels with specificity for Cx50 over its closely related homologue Cx46. Here, we examined the mechanism of BQ+ action using undocked Cx46 and Cx50 hemichannels, which are more amenable to analyses at the single-channel level. We found that BQ+ (300 µM–1 mM) robustly inhibited Cx50, but not Cx46, hemichannel currents, indicating that the Cx selectivity of BQ+ is preserved in both hemichannel and GJ channel configurations. BQ+ reduced Cx50 hemichannel open probability (Po) without appreciably altering unitary conductance of the fully open state and was effective when added from either extracellular or cytoplasmic sides. The reductions in Po were dependent on BQ+ concentration with a Hill coefficient of 1.8, suggesting binding of at least two BQ+ molecules. Inhibition by BQ+ was voltage dependent, promoted by hyperpolarization from the extracellular side and conversely by depolarization from the cytoplasmic side. These results are consistent with binding of BQ+ in the pore. Substitution of the N-terminal (NT) domain of Cx46 into Cx50 significantly impaired inhibition by BQ+. The NT domain contributes to the formation of the wide cytoplasmic vestibule of the pore and, thus, may contribute to the binding of BQ+. Single-channel analyses showed that BQ+ induced transitions that did not resemble pore block, but rather transitions indistinguishable from the intrinsic gating events ascribed to loop gating, one of two mechanisms that gate Cx channels. Moreover, BQ+ decreased mean open time and increased mean closed time, indicating that inhibition consists of an increase in hemichannel closing rate as well as a stabilization of the closed state. Collectively, these data suggest a mechanism of action for BQ+ that involves modulation loop gating rather than channel block as a result of binding in the NT domain

Colocalization of connexin 36 and corticotropin-releasing hormone in the mouse brain

<p>Abstract</p> <p>Background</p> <p>Gap junction proteins, connexins, are expressed in most endocrine and exocrine glands in the body and are at least in some glands crucial for the hormonal secretion. To what extent connexins are expressed in neurons releasing hormones or neuropeptides from or within the central nervous system is, however, unknown. Previous studies provide indirect evidence for gap junction coupling between subsets of neuropeptide-containing neurons in the paraventricular nucleus (PVN) of the hypothalamus. Here we employ double labeling and retrograde tracing methods to investigate to what extent neuroendocrine and neuropeptide-containing neurons of the hypothalamus and brainstem express the neuronal gap junction protein connexin 36.</p> <p>Results</p> <p>Western blot analysis showed that connexin 36 is expressed in the PVN. In bacterial artificial chromosome transgenic mice, which specifically express the reporter gene Enhanced Green Fluorescent Protein (EGFP) under the control of the connexin 36 gene promoter, EGFP expression was detected in magnocellular (neuroendocrine) and in parvocellular neurons of the PVN. Although no EGFP/connexin36 expression was seen in neurons containing oxytocin or vasopressin, EGFP/connexin36 was found in subsets of PVN neurons containing corticotropin-releasing hormone (CRH), and in somatostatin neurons located along the third ventricle. Moreover, CRH neurons in brainstem areas, including the lateral parabrachial nucleus, also expressed EGFP/connexin 36.</p> <p>Conclusion</p> <p>Our data indicate that connexin 36 is expressed in subsets of neuroendocrine and CRH neurons in specific nuclei of the hypothalamus and brainstem.</p

Microhabitat occupation and functional morphology of four species of sympatric agamid lizards in the Kyzylkum Desert, central Uzbekistán

We examined microhabitat occupation and functional morphology of four sympatric agamid lizards (Phrynocephalus helioscopus helioscopus, P. interscapularis, P. mystaceus galli and Trapelus sanguinolentus) at three sites in the arid zone of central Uzbekistan. At two sites located in sand dunes, substrate attributes played a key role in habitat selection by three syntopic species. At a third flat, stony site, P. helioscopus selected habitat non–randomly, tending to occur close to sparse, low vegetation. Syntopic taxa were separated in morphospace, and there was a trend for taxa with proportionally longer limbs to have faster field escape speeds. Field escape distances and predator avoidance tactics differed between species, with two main escape strategies (crypsis or sand–diving following an escape sprint). We caution that broad–scale threatening processes such as over–grazing and salinity may be having a detrimental effect on microhabitat features important to terrestrial reptiles in Uzbekistan

An automated iridium-strip heater for LA-ICP-MS bulk analysis of geological samples

In this paper we describe a flux-free fusion technique for the highly precise LA-ICP-MS bulk analysis of geological samples. For this purpose we have developed an automated iridium-strip heater with temperature and melt time control. To optimise the homogeneity of the fused glasses and to reduce possible depletion of volatile elements during melting, we undertook experiments with basaltic rock and glass powders using different melting temperatures (1300-1700 °C) and melting times (5-80 s). Major and trace element microanalysis was performed using EPMA and LA-ICP-MS. Homogeneous glasses were obtained for temperatures ≥ 1500 °C and melting times ≥ 10 s. High loss (20-90%) of highly volatile elements (e.g., Cs, Ge, Sn, Pb) was observed for high melting temperatures (≥ 1600 °C) and long melting times (80 s). Standard melting conditions (1600 °C, 10 s) represent a compromise, as the glasses were homogeneous with respect to major and trace elements and, at the same time, were not depleted in elements with condensation temperatures (at a pressure of 10-4 bar) higher than about 900 K (e.g., Zr, Hf, Ba, Sr, REE, U, Mo, Ni, Rb, Ga). Several international geological reference materials with SiO2 ranging between 47% m/m and 59% m/m were prepared using our standard melting conditions (1600 °C, 10 s) and subsequently analysed by LA-ICP-MS. These samples also include the new Brazilian basaltic reference material BRP-1. Matrix-matched calibration of the LA-ICP-MS data was performed using the basaltic reference glasses KL2-G, ML3B-G, BCR-2G and BHVO-2G. Most analytical data agreed within uncertainty at the 95% confidence level with the GeoReM preferred values published in the GeoReM database for reference materials of geological and environmental interest. To demonstrate routine bulk LA-ICP-MS analyses of geochemical and cosmochemical samples using the whole rock fusion technique, we also present trace element data for ocean island basalts from Lanai (Hawaii) and of Martian meteorites. © 2008 International Association of Geoanalysts