Electrical and adaptive properties of rod photoreceptors in bufo marinus. I. Effects of altered extracellular Ca(2+) levels

The effects of altering extracellular Ca(2+) levels on the electrical and adaptive properties of toad rods have been examined. The retina was continually superfused in control (1.6 mM Ca(2+)) or test ringer’s solutions, and rod electrical activity was recorded intracellularly. Low-calcium ringer’s (10(-9)M Ca(2+)) superfused for up to 6 min caused a substantial depolarization of the resting membrane potential, an increase in light-evoked response amplitudes, and a change in the waveform of the light-evoked responses. High Ca(2+) ringer’s (3.2 mM) hyperpolarized the cell membrane and decreased response amplitudes. However, under conditions of either low or high Ca(2+) superfusion for up to 6 min, in both dark-adapted and partially light-adapted states, receptor sensitivity was virtually unaffected; i.e., the V-log I curve for the receptor potential was always located on the intensity scale at a position predicted by the prevailing light level, not by Ca(2+) concentration. Thus, we speculate that cytosol Ca(2+) concentration is capable of regulating membrane potential levels and light-evoked response amplitudes, but not the major component of rod sensitivity. Low Ca(2+) ringer’s also shortened the period of receptor response saturation after a bright but nonbleaching light flash, hence accelerating the onset of both membrane potential and sensitivity recovery during dark adaptation.

Exposure of the retina to low Ca(2+) (10(-9)M) ringer’s for long periods (7-15 min) caused dark-adapted rods to lose responsiveness. Response amplitudes gradually decreased, and the rods became desensitized. These severe conditions of low Ca(2+) caused changes in the dark-adapted rod that mimic those observed in rods during light adaptation. We suggest that loss of receptor sensitivity during prolonged exposure to low Ca(2+) ringer’s results from a decrease of intracellular (intradisk) stores of Ca(2+); i.e., less Ca(2+) is thereby released per quantum catch.

     

Assembly and disassembly of mammalian chromosome pellicle

By means of indirect double immunofluorescent staining,the coordination of PI antigen and perichromonucleolin(PCN),the constituent of nuclear periphery and nucleolus respectively,in the assembly and disassembly of chromosome pellicle during mitosis was studied.It was found that in 3T3 cells,during mitosis PI antigen began to coat the condensing chromosome surface earlier than PCN did.However,both of them completed their coating on chromosome at approximately the same stage of mitosis,prometaphase metaphase,The dissociation of mitosis,Prometaphase metaphase.The dissociation of PI antigen from chromosome pellicle to participate the formation of nuclear periphery took place also ahead of that of PCN,At early telophase PI antigen had been extensively involved in the formation of nuclear periphery,while PCN remained in association with the surface of decondensing chromosomes.At late telophase,when PI antigen was localized in an fairly well formed nuclear periphery,PCN was in a stage of forming prenucleolar bodies.     

Influence of Ileo-Caecal Cannulation and Oxytetracycline on Ileo-Caecal and Rectal Coliform Populations in Pigs

The effect of surgery (insertion of an ileo-caecal cannula) and a subsequent parenteral treatment with oxytetracycline on the ileo-caecal and rectal coliform populations in 7 Swedish Yorkshire castrates were studied. Samples were collected during surgery as well as 3, 7, 14 and 20 days post surgery. The diversity of the enteric coliform flora was initially high both in the ileo-caecal ostium and in rectum. No alteration in the diversity of the enteric coliform flora was observed following surgery and treatment with oxytetracycline. As the insertion of ileo-caecal cannulas did not affect the intestinal coliform flora this study gives support to the use of this technique to mirror processes in the small intestine of pigs. Further, the diversity of the enteric coliform flora was unaffected by the parenteral treatment with oxytetracycline.     

Milk composition and growth in wild and captive Tasmanian bettongs,<Emphasis Type="Italic"> Bettongia gaimardi</Emphasis> (Marsupialia)

Changes in milk composition (total solids, carbohydrate, protein, lipid and calculated gross energy content) during lactation in three groups of Tasmanian bettongs ( Bettongia gaimardi): free-living animals (wild group), captive animals offered a diet of dry dog food and apples ad libitum (ad lib group), and captive animals fed restricted amounts of the same diet (maintenance group) were related to growth rates (measured as body mass and head length) of their young. There were no significant differences in the concentration of milk solids among the three groups, but the wild group had higher lipid concentrations and the maintenance group had higher carbohydrate but lower protein concentrations. For all three groups, milk total solids increased through lactation from ca. 25% to ca. 45% and carbohydrate concentrations decreased from ca. 18% to about 3%. Protein concentrations increased from ca. 5% to ca. 10% in the wild and ad lib groups, but only from 4% to 8% in the maintenance group. Lipid concentrations increased in the wild and ad lib groups from ca. 4% to ca. 18%, but in the maintenance group only to ca. 7%. Calculated gross energy content of milk increased through lactation in the wild and ad lib groups (from ca. 500 kJ.100 ml(-1) to ca. 1,000 kJ.100 ml(-1)), but there was no significant increase in the maintenance group. The volume of milk produced increased to a peak just prior to permanent pouch vacation by the young, when the gross energy output in milk was 120-150 kJ.3 h(-1) in the wild and ad lib groups. On a daily basis this is equivalent to the milk energy output of larger wallabies, and helps to explain the relatively high growth rates of young Tasmanian bettongs. There were significant differences in growth rates among the groups, with the heaviest young always in the ad lib group. Thus differences in milk composition resulting from different planes of nutrition can lead to differences in growth rates of marsupial young.     

Hormonally regulated programmed cell death in barley aleurone cells

Cell death was studied in barley (cv Himalaya) aleurone cells treated with abscisic acid and gibberellin. Aleurone protoplasts incubated in abscisic acid remained viable in culture for at least 3 weeks, but exposure to gibberellin initiated a series of events that resulted in death. Between 4 and 8 days after incubation in gibberellin, >70% of all protoplasts died. Death, which occurred after cells became highly vacuolated, was manifest by an abrupt loss of plasma membrane integrity followed by rapid shrinkage of the cell corpse. Hydrolysis of DNA began before death and occurred as protoplasts ceased production of alpha-amylase. DNA degradation did not result in the accumulation of discrete low molecular weight fragments. DNA degradation and cell death were prevented by LY83583, an inhibitor of gibberellin signaling in barley aleurone. We conclude that cell death in aleurone cells is hormonally regulated and is the final step of a developmental program that promotes successful seedling establishment.     

Concentrations and ecological risks of metals in surface sediments of some coastal creeks in the Niger Delta,Nigeria

The concentrations of nine metals were measured by atomic absorption spectrophotometry in surface sediments of three coastal creeks, namely, the Ifie, Egbokodo and Ubeji creeks, in the Niger Delta of Nigeria, from August 2012 to January 2013. The aim of the study was to provide information on the spatial and seasonal distribution patterns, degree of contamination, and ecological risks of metals in these sediments. The mean concentrations of the nine metals in these creek sediments ranged from 0.30 to 3.20?mg kg^?1 Cd; 10.7 to 24.7?mg kg^?1 Pb, 125 to 466?mg kg^?1 Cr; 3.1.10 to 14.9?mg kg^?1 Cu; 4.7 to 14.3?mg kg^?1 Co; 61.1 to 115?mg kg^?1 Ni; 106 to 183?mg kg^?1 Mn; 52.0 to 170?mg kg^?1 Zn and 5 469 to 20 639?mg kg^?1 Fe. In general, the metal concentrations were higher in the dry season than the wet season, except for Cr. The concentrations of Cd, Cr, Ni and Zn were above their regulatory control limits in sediment as specified by the Nigerian Regulatory Authority and Cd was identified as the main ecological risk factor. The enrichment factors for the studied metals followed the order: Cd > Cr > Ni > Zn > Pb > Co > Mn > Cu. The average multiple pollution index values indicated that these sediments were severely polluted with significant inputs from Cd, Ni and Cr.     

Genetic islands of <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> strains NEM316 and 2603VR and their presence in other Group B Streptococcal strains

Background  

Streptococcus agalactiae (Group B Streptococcus; GBS) is a major contributor to obstetric and neonatal bacterial sepsis. Serotype III strains cause the majority of late-onset sepsis and meningitis in babies, and thus appear to have an enhanced invasive capacity compared with the other serotypes that cause disease predominantly in immunocompromised pregnant women. We compared the serotype III and V whole genome sequences, strains NEM316 and 2603VR respectively, in an attempt to identify genetic attributes of strain NEM316 that might explain the propensity of strain NEM316 to cause late-onset disease in babies. Fourteen putative pathogenicity islands were described in the strain NEM316 whole genome sequence. Using PCR- and targeted microarray- strategies, the presence of these islands were assessed in a diverse strain collection including 18 colonizing isolates from healthy pregnant women, and 13 and 8 invasive isolates from infants with early- and late-onset sepsis, respectively.