Patch-clamp study of isolated taste receptor cells of the frog

Summary Taste discs were dissected from the tongue ofR. ridibunda and their cells dissociated by a collagenase/low Ca/mechanical agitation protocol. The resulting cell suspension contained globular epithelial cells and, in smaller number, taste receptor cells. These were identified by staining properties and by their preserved apical process, the tip of which often remained attached to an epithelial (associated) cell. When the patch pipette contained 110mm KCl and the cells were superfused with NaCl Ringer's during whole-cell recording, the mean zero-current potential of 22 taste receptor cells was –65.2 mV and the slope resistance 150 to 750 M. Pulse-depolarization from a holding voltage of –80 mV activated a transient TTX-blockable inward Na current. Activation became noticeable at –25 mV and was half-maximal at –8 mV. Steady-state inactivation was half-maximal at –67 mV and complete at –50 mV. Peak Na current averaged –0.5 nA/cell. The Ca-ionophore A23187 shifted the activation and inactivation curve to more negative voltages. Similar shifts occurred when the pipette Ca was raised. External Ni (5mm) shifted the activation curve towards positive voltages by 10 mV. Pulse depolarization also activated outward K currents. Activation was slower than that of Na current and inactivation slower still. External TEA (7.5mm) and 4-aminopyridine (1mm) did not block, but 5mm Ba blocked the K currents. K-tail currents were seen on termination of depolarizing voltage pulses. A23187 shifted theI _K(V)-curve to more negative voltages. Action potentials were recorded when passing pulses of depolarizing outward current. Of the frog gustatory stimulants, 10mm Ca caused a reversible 5-to 10-mV depolarization in the current-clamp mode. Quinine (0.1mm, bitter) produced a reversible depolarization accompanied by a full block of Na current and, with slower time-course, a partial block of K currents. Cyclic AMP (5mm in the external solution or 0.5 m in the pipette) caused reversible depolarization (to –40 to –20 mV) due to partial blockage of K currents, but only if ATP was added to the pipette solution. Similar responses were elicited by stimulating the adenylate cyclase with forskolin. Blockage of cAMP-phosphodiesterase enhanced the response to cAMP. These results suggest that cAMP may be one of the cytosolic messengers in taste receptor cells. Replacement of ATP by AMP-PNP in the pipette abolished the depolarizing response to cAMP. Inclusion of ATP--S in the pipette caused slow depolarization to –40 to –20 mV, due to partial blockage of K currents. Subsequently, cAMP was without effect. The remaining K currents were blockable by Ba. These results suggest that cAMP initiates phosphorylation of one set of K channels to a nonconducting conformation.     

TheRT1.G locus in the rat encodes a Qa/TL-like antigen

A new antigenic system in the rat homologous to theQa/TL antigen system in the mouse has been characterized. It was detected by antibodies raised in donor-recipient combinations that were matched for theRT1. A, B, D, E loci in the major histocompatibility complex (MHC): (R11×BN)F₁ anti-BN.1L(LEW), (R18×BN)F₁ anti-BN.1L, and BN.1LV1(F344) anti-BN.1L. Absorption analyses using these antisera and a variety of inbred, congenic and recombinant strains identified three alleles,RT1.G ^a ,G ^b ,G ^c , of whichG ^c is a null allele. The strain distribution of these alleles was determined, using 37 strains of rats representative of all of the prototypic haplotypes and a number of congenic and recombinant strains. The use of the congenic and recombinant strains showed that theRT1.G locus was linked to the MHC and that the most probable gene order wasA-E-G. Testcross analysis showed that the map distance betweenA andG was 1.4 cM(4/285 recombinants). The RT1.G antigen has a heavy chain ofM _r 46 000 and is present on both T and B cells.     

Biochemical characterization of chromatin fractions isolated from induced and uninduced friend erythroleukemia cells

Summary Chromatin fractions from Friend erythroleukemia cells after induction of differentiation by dimethylsulfoxide (DMSO) were compared in their biochemical characteristics to fractions from uninduced cells. Fractions were prepared by extracting chromatin from nuclei after mild micrococcal nuclease treatment with increasing concentrations of NaCl according to Sanders [1]. This procedure has been found to release chromatin containing hyperacetylated histones preferentially [2]. The fractions obtained by this procedure were analysed in respect to the amount of chromatin released, the amount of histone H1, the degree of acetylation of histone H4, the presence of non-histone proteins and the concentration of transcribed and non-transcribed sequences. It was found that the fractions differ in the amount of histone H1 present, in several non-histone proteins and in the acetylation of histonie H4, regardless whether induced or uninduced cells were analysed. The distribution of transcribed sequences versus non-transcribed sequences among the fractions was the same, demonstrating that this fractionation procedure, although leading to fractions with biochemical differences, is not able to discriminate functional states of chromatin and that the biochemical characteristics of the fractions may be common to both, active as well as inactive states of chromatin.     

Disruption of the Rad52 Gene Alters the Spectrum of Spontaneous Sup4-O Mutations in Saccharomyces Cerevisiae

Defects in the RAD52 gene of the yeast Saccharomyces cerevisiae confer a mutator phenotype. To characterize this effect in detail, a collection of 238 spontaneous SUP4-o mutations arising in a strain having a disrupted RAD52 gene was analyzed by DNA sequencing. The resulting mutational spectrum was compared to that derived from an examination of 222 spontaneous mutations selected in a nearisogenic wild-type (RAD52) strain. This comparison revealed that the mutator phenotype was associated with an increase in the frequency of base-pair substitutions. All possible types of substitution were detected but there was a reduction in the relative fraction of A.T----G.C transitions and an increase in the proportion of G.C----C.G transversions. These changes were sufficient to cause a twofold greater preference for substitutions at G.C sites in the rad52 strain despite a decrease in the fraction of G.C----T.A transversions. There were also considerable differences between the distributions of substitutions within the SUP4-o gene. Base-pair changes occurred at fewer sites in the rad52 strain but the mutated sites included several that were not detected in the RAD52 background. Only two of the four sites that were mutated most frequently in the rad52 strain were also prominent in the wild-type strain and mutation frequencies at almost all sites common to both strains were greater for the rad52 derivative. Although single base-pair deletions occurred in the two strains with similar frequencies, several classes of mutation that were recovered in the wild-type background including multiple base-pair deletions, insertions of the yeast transposable element Ty, and more complex changes, were not detected in the rad52 strain.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cyanase-mediated utilization of cyanate in Pseudomonas fluorescens NCIB 11764.

Pseudomonas fluorescens NCIB 11764 was capable of utilizing cyanate (OCN-) as a sole nitrogen source for growth. Crude cell extracts from cells grown on cyanate, but not on ammonium sulfate, were induced for an enzyme catalyzing cyanate conversion to ammonia. Enzymatic activity was shown to be bicarbonate dependent and specific for cyanate as a substrate, suggesting that cyanate utilization in this organism is facilitated by an enzyme resembling cyanase (cyanate amidohydrolase; EC 3.5.5.3), as described previously in Escherichia coli and Flavobacterium sp.     

Die Verbreitung des Weidensperlings (Passer hispaniolensis) in Marokko

Zusammenfassung In Marokko fällt die südliche Verbreitungsgrenze des Weidensperlings wahrscheinlich mit dem Nordrand des Antiatlas zusammen. Aus den Oasen der ehemaligen Spanischen Sahara liegen keine Beobachtungen vor. Aus dem Raum Oujda sind die östlichsten Populationen, die ständig zwischen Marokko und Algerien migrieren, bekannt. Landnutzung und Klima prägen entscheidend die Dispersion des Weidensperlings. Als euryöke Art ist er in der Lage, das reichhaltige Angebot an Schlaf- und Brutplätzen sowie an Nahrung und Wasser in den ackerbaulichen Nutzflächen zu verwerten. Auffallend ist, daß die Hauptverbreitungszonen mit den großen ackerbaulichen Nutzflächen zusammenfallen. Während die agrarischen Nutzflächen sich in den letzten Jahrzehnten im Zuge der Modernisierung der Landwirtschaft rapide änderten, und das erklärte Ziel für das Jahr 2000 in einer bewässerten Fläche von einer Million Hektar besteht, gingen die ursprünglichen Habitate des Weidensperlings, wie die Bereiche der mauretanischen Wüstensteppengebiete, drastisch zurück. Ferner konnte im Raum Marrakech eine Abnahme der Niederschläge beobachtet werden, die das für die Weidensperlinge verfügbare Nahrungsangebot entscheidend beeinflußt und somit die Populationsdynamik steuert.

---

On the distribution of the Spanish Sparrow (Passer hispaniolensis) in Morocco

Summary In Morocco, the southernmost border of the distribution of the Spanish Sparrow coincides probably with the North-Antiatlas. From the oasis of the former Spanish Sahara don't exist any observations. In the region of Oujda the easternmost populations are found which are migrating permanently between Morocco and Algeria. The euryoecous species is able to use a high variability of different roosts, breeding sites, resources of food and water in the agricultural areas. A high overlap of the main distribution areas with the large agricultural regions is obvious. While the cultivated areas have been changed heavily during the modernisation periode of the Moroccan agriculture the original habitats of the Spanish Sparrow (i. e. the parts in the Mauretanian desert-steppe regions) disappeared dramatically. The goal of the year 2000 lies in an irrigated scheme of 1.000.000 ha. Moreover, a decrease of the precipitation in the region of Marrakech was observed, which has a great influence on the food available for the species and which therefore controls the population dynamics.

     

Histopathology and cell culture characteristics of liver cells from grc − and grc + rats given diethylnitrosamine

The histopathological response and cell culture characteristics of liver cells from the R16 (grc ^–) strain of rats, which carries an MHC-linked deletion, were examined one week after a single intraperitoneal injection of 200 mg/ kg body weight diethylnitrosamine (DEN) and were compared with the response of liver cells from wild type (grc+) rats. The DEN exposure induced hydropicl vacuolar changes in the parenchymal cells and a limited proliferation of oval cells in the periportal areas of the livers of both grc+ and grc rats. Primary culture of collagenase-digested livers consisted of parenchymal, bile ductular and oval-related cells as determined by cell-specific immunohistochemistry. Subpassaged cells from grc+ rats exhibited oval cell ultrastructural morphology, inducible histochemical staining for gammaglutamyl transpeptidase (GGT), and DEN-associated onset of anchorage-independent growth. Primary cultures of liver cells from R16 rats consistently failed to form cell strains upon subpassage.Abbreviations DEN diethylnitrosamine - grc growth and reproduction complex - GGT gamma-glutamyl transpeptidase - MHC major histocompatibility complex