Effects of a reduction in the number of gap junction channels or in their conductance on ischemia-reperfusion arrhythmias in isolated mouse hearts

A transient reduction of cell coupling during reperfusion limits myocardial necrosis, but little is known about its arrhythmogenic effects during ischemia-reperfusion. Thus, we analyzed the effect of an extreme reduction in the number of gap junction channels or in their unitary conductance on ventricular arrhythmias during myocardial ischemia-reperfusion. Available gap junction uncouplers have electrophysiological effects independent from their uncoupling actions. Thus, isolated hearts from Cx43(Cre-ER(T)/fl) mice treated with 4-hydroxytamoxifen (4-OHT), from Cx43KI32 mice [in which connexin (Cx)43 was replaced with Cx32], and from control animals were submitted to regional ischemia and reperfusion, and spontaneous and induced ventricular arrhythmias were monitored. In additional hearts, changes in activation time and electrical impedance during global ischemia-reperfusion were assessed. In contrast to treatment with 4-OHT, replacement of Cx43 with Cx32 did not modify baseline activation time or electrical impedance. However, the number of extrasistole and ventricular tachyarrhythmias was higher in isolated hearts from Cx43KI32 and 4-OHT-treated Cx43(Cre-ER(T)/fl) animals versus wild-type animals during normoxia, ischemia (12.29 ± 3.26 and 52.17 ± 22.51 vs. 3.00 ± 1.46 spontaneous tachyarrhythmias, P < 0.05), and reperfusion. The impairment in conduction during ischemia was steeper in isolated hearts from Cx43KI32 animals, whereas changes in myocardial impedance were attenuated during ischemia in both transgenic models, suggesting altered cell-to-cell coupling at baseline. In conclusion, both reduction of Cx43 with 4-OHT and replacement of Cx43 by less-conductive Cx32 were arrhythmogenic under normoxia and ischemia-reperfusion, despite no major effects on baseline electrical properties. These results suggest that modifications in gap junction communication silent under normal conditions may be arrhythmogenic during ischemia-reperfusion.     

Effects of fragmentation and hybridization on geographical patterns of song variation in the endangered Yellow Cardinal Gubernatrix cristata

The song learning process may lead to small‐scale geographical variation in vocalizations of oscine birds. This variation can be further enhanced by the effects of habitat fragmentation or hybridization. Populations of the endangered Yellow Cardinal Gubernatrix cristata are now patchily distributed in the southern South American thorny shrubland forests and are small as a consequence of the pressure exerted by increased habitat transformation and illegal trade. We study the Yellow Cardinal's vocalizations throughout its distribution and assess how habitat characteristics and fragmentation, as well as hybridization with the Common Diuca Diuca diuca, have affected song patterns of different populations. We expected to find song differences among populations and songs to be more similar to those of the Common Diuca in areas where hybridization occurs. Multivariate analyses revealed significant differences in song between the four populations studied and confirmed that songs are more similar to those of Common Diuca where hybridization takes place. These results, in conjunction with genetic studies, can help to establish management units that preserve genetic and cultural variation in this endangered species.     

Effects of arbuscular mycorrhizal fungal species and the medium pH on the growth of Pueraria phaseoloides (Roxb.) Benth

Soil conditions may change the response of plants to inoculation with arbuscular mycorrhizal fungi (AMF). This, in turn, may influence the development of mycorrhizal associations. The effect of AM species isolated from different ecosystems was evaluated on Pueraria phaseoloides (kudzu). Experiments were conducted under controlled conditions in Leonard jars, on a substrate made of peat, rice husk, and vermiculite (1-1-1) enriched with rock phosphate plus a modified Hoagland nutrient solution. In the first experiment the initial pH of the substrate (8.0) was reduced by approximately one unit by inoculation with Kuklospora colombiana, Glomus clarum, and Glomus manihotis. The result was the same for Acaulospora longula species when 4-morpholine ethanesulphonic acid (MES) buffer was used. The final pH of the substrate was correlated with the above-ground plant biomass production suggesting that the most effective fungus regulated the pH of the substrate. This positive interaction leads to a higher concentration of P and K in plants. When the pH of the substrate was buffered with MES, in the second experiment, the efficiency of K. colombiana was reduced, even though plants inoculated with this fungus yielded more than non-inoculated plants. G. intraradices and A. longula were favoured by buffer addition. Beneficial buffer effects on this plant resulted in lower pH, better plant P and K uptake, and higher biomass production. The best plant yield was obtained at pH 7.0 in both experiments. G. clarum and G. manihotis yielded the highest biomass production. Under the proposed conditions, AMF improved P. phaseoloides growth and pH regulation. These growth conditions may be used for the evaluation and propagation of some AMF species adding MES buffer in the nutrient solution.     

Peptides of the liver stage antigen-1 (LSA-1) of Plasmodium falciparum bind to human hepatocytes

Synthetic peptides from the liver stage antigen-1 (LSA-1) antigen sequence were used in HepG2 cell and erythrocyte binding assays to identify regions that could be involved in parasite invasion. LSA-1 protein peptides 20630 ((21)INGKIIKNSEKDEIIKSNLRY(40)), 20637 ((157)KEKLQGQQSDSEQERRAY(173)), 20638 ((174)KEKLQEQQSDLEQERLAY(190)) and 20639 (191KEKLQEQQSDLEQERRAY(207)) had high binding activity in HepG2 assays. Were located in immunogenic regions; peptide cell binding was saturable. Peptide 20630 bound specifically to 48kDa HepG2 membrane surface protein. LSA-1 peptides 20630 ((21)INGKIIKNSEKDEIIKSNLRY(40)) and 20633 ((81)DKELTMSNVKNVSQTNFKSLY(100)) showed specific erythrocyte binding activity and inhibited merozoite invasion of erythrocytes in vitro. A monkey serum prepared against LSA-1 20630 peptide analog (CGINGKNIKNAEKPMIIKSNLRGC) inhibited merozoite invasion in vitro. The data suggest LSA-1 "High Activity Binding Peptides" could play a possible role in hepatic cell invasion as well as merozoite invasion of erythrocytes.     

A comparison of HPLC pigment analyses and biovolume estimates of phytoplankton groups in an oligotrophic lake

Assessment of the contribution of distinct algal groups to phytoplanktonbiomass in oligotrophic lakes by marker pigments is comparedwith assessment by cell-counting biovolume estimates. Seasonalsamples from an oligotrophic alpine lake (Redon, Pyrenees) mostlyincluded species of chrysophytes, dinoflagellates, cryptophytesand chlorophytes. The chlorophyl a (Chl a) corresponding toeach algal group was estimated using HPLC pigment analyses andthe CHEMTAX program. Chl a estimates and biovolume showed asignificant correlation for all the groups during the ice-freeseason except for chlorophytes. However, some of the samplesfrom the initial phase of the ice cover presented a clear departurefrom the relationship during the ice-free period in most groups.On the other hand, the ratios between a specific marker pigmentand the biovolume of the marked algal group were significantlyconstant within the photic zone (>1% surface irradiance)for most of the pigments and groups, including chlorophytes.Nevertheless, the ratios increased and showed a large variabilityfor samples below the photic depth or below the ice cover. Theviolaxanthin-chrysophyte biovolume ratio presented an opposedtendency to other pigment-biovolume ratios, which increasedin inverse proportion to the depth of the sample. The resultsare discussed in terms of methodological limitations, acclimationresponses and species composition.     

Hybridization screening of very short PCR products for paleoepidemiological studies of Chagas' disease

Single strands of very short PCR products can be covalently immobilized to a slide and then easily detected by probe hybridization. In this work, the PCR product was a 70-nucleotide segment of ancient DNA, representing a portion of repeat mini-circle DNA from the kinetoplast of Trypanosoma cruzi, the infectious agent of Chagas' disease (American Trypanosomiasis). The target segment was initially established to be present in soft tissue samples taken from four "naturally" mummified Andean bodies using PCR followed by cloning and sequencing. Hybridization screening of the covalently immobilized PCR products positively identified products from 25 of 27 specimens of different tissues from these four mummies. The method appears to be ideal for the purpose of screening a large number of specimens when the target PCR product is very short.     

Ligand-induced caveolae-mediated internalization of A1 adenosine receptors: morphological evidence of endosomal sorting and receptor recycling

The involvement of caveolae in the internalization of A(1) adenosine receptors (A(1)R) and the receptor sorting and recycling was studied in the smooth muscle cell line DDT(1)MF-2, by binding assays, by confocal microscopy, and at the structural level. The use of cholera toxin-binding subunit adsorbed to gold as a specific probe for labeling the ganglioside GM(1) and immunoelectron microscopy techniques showed that agonist stimulation produced a clustering and sequestration of adenosine receptors in caveolae. Furthermore, pull-down experiments showed there to be a direct interaction between the C-terminal domain of A(1)R and caveolin-1. Addition of exogenous adenosine deaminase (ADA), a protein that binds to A(1)R and acts as a receptor activity modifying protein (RAMP) stimulated R-PIA-induced A(1) receptor internalization. Finally, the sorting and recycling of A(1)R/ADA complexes was analyzed. Detailed electron microscopy revealed that A(1)R/ADA complexes internalize together through caveolae, are differentially sorted in endosomes, and are recycled back to the cell surface by different groups of recycling endosomes. These results give insight into the spatiotemporal regulation and traffic of A(1)R and RAMPs.