Na+ competes with K+ in bumetanide-sensitive transport by Malpighian tubules of Rhodnius prolixus.
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We examined the effects of bathing saline Na+/K+ ratio, bumetanide and hydrochlorothiazide on fluid and ion transport by serotonin-stimulated Malpighian tubules of Rhodnius prolixus. Previous pharmacological and electrophysiological studies indicate that a bumetanide-sensitive Na+/K+/2Cl- cotransporter is the primary route for basolateral ion entry into the cell during fluid secretion. The goal of this study was to resolve the apparent conflict between relatively high secretion rates by tubules bathed in K+-free saline and the evidence that Na+/K+/2Cl- cotransporters described in other systems have an absolute requirement for all three ions for translocation. Our measurements of fluid secretion rate, ion fluxes and electrophysiological responses to serotonin show that fluid secretion in K+-free saline is bumetanide sensitive and hydrochlorothiazide insensitive. Dose-response curves of secretion rate versus bumetanide concentration were identical for tubules bathed in K+-free and control saline with IC50 values of 2.6 x 10(-6) mmol l(-1) and 2.9 x 10(-6) mmol l(-1), respectively. Double-reciprocal plots of K+ flux versus bathing saline K+ concentration showed that increasing Na+ concentration in the bathing fluid increased Kt but had no effect on Jmax, consistent with competitive inhibition of K+ transport by Na+. We propose that the competition between Na+ and K+ for transport by the bumetanide-sensitive transporter is part of an autonomous mechanism by which Malpighian tubules regulate haemolymph K+ concentration. (+info)
Mixed domestic infestation by Rhodnius prolixus Stal, 1859 and Panstrongylus geniculatus Latreille, 1811, vector incrimination, and seroprevalence for Trypanosoma cruzi among inhabitants in El Guamito, Lara State, Venezuela.
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Mixed infestation of nymphs and adults of Rhodnius prolixus Stal, 1859 and Panstrongylus geniculatus Latreille, 1811 was detected in 3 (15%) of 20 dwellings in El Guamito, an endemic focus of Chagas disease in Lara State, Venezuela. In one of the houses, both species were positive for Trypanosoma cruzi: 14.3% (R. prolixus) and 20% (P. geniculatus ). The overall infection rate in 143 of 352 R. prolixus was 16.1%. Parasites isolated from R. prolixus were identified as T. cruzi I by random amplified polymorphic DNA analysis. Dot-enzyme-linked immunosorbent assays of 36 R. prolixus showed that 58.3% of the R. prolixus had fed on humans. The gut contents of one fifth-instar nymph of P. geniculatus that was positive for T. cruzi also reacted with anti-human serum. A questionnaire was used to gather data on the demographic and socioeconomic characteristics of the population. An indirect immunofluorescent test, an indirect hemaglutination test, and an ELISA were used to detect the presence of antibodies against T. cruzi in 84 of 86 inhabitants and in 15.5% of people more than 20 years old. The relative risk (RR) of infection was greater in men than in women (RR = 1.61, 95% confidence interval = 0.54-4.80). Of the people more than 15 years old, 36.6% had no formal education. All respondents recognized triatomine bugs, but they did not relate them to Chagas disease transmission. A total of 85.7% of the houses were "ranchos" suitable for the colonization of triatomine bugs. The possible domiciliation of P. geniculatus and the implications of competition with R. prolixus for resources are discussed. Since there is no clear separation of food sources, abiotic factors such as microclimatic variation within houses may be critical to predict the outcome of the process of competition and potential domestication of this generally sylvatic species. (+info)
Enzootic transmission of Trypanosoma cruzi and T. rangeli in the Federal District of Brazil.
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The Federal District of Brazil (DF) lies within the Cerrado biome, where open shrubland (savannas) is interspersed with riverside gallery forests and permanent swamps (veredas). Trypanosoma cruzi-infected native triatomines occur in the area, but the enzootic transmission of trypanosomatids remains poorly characterized. A parasitological survey involving sylvatic triatomines (166 Rhodnius neglectus collected from Mauritia flexuosa palms) and small mammals (98 marsupials and 70 rodents, totaling 18 species) was conducted in 18 sites (mainly gallery forests and veredas) of the DF. Parasites were isolated, morphologically identified, and characterized by PCR of nuclear (mini-exon gene) and kinetoplast DNA (kDNA). Six R. neglectus, seven Didelphis albiventris and one Akodon cursor were infected by trypanosomes; wild reservoir infection is documented for the first time in the DF. kDNA PCR detected T. cruzi in five R. neglectus and mini-exon gene PCR revealed T. cruzi I in isolates from D. albiventris. Parasites infecting one bug yielded T. rangeli KP1+ kDNA amplicons. In spite of the occurrence of T. cruzi-infected D. albiventris (an important wild and peridomestic reservoir) and R. neglectus (a secondary vector displaying synanthropic behavior), a low-risk of human Chagas disease transmission could be expected in the DF, considering the low prevalence infection recorded in this work. The detection of T. rangeli KP1+ associated with R. neglectus in the DF widens the known range of this parasite in Brazil and reinforces the hypothesis of adaptation of T. rangeli populations (KP1+ and KP1-) to distinct evolutionary Rhodnius lineages. (+info)
The role of salivary lipocalins in blood feeding by Rhodnius prolixus.
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In order to overcome host mechanisms that prevent blood loss, the blood-sucking bug Rhodnius prolixus has evolved a complex salivary secretion containing dozens of different proteins. A number of these have been characterized and found to have roles in inhibiting various hemostatic or inflammatory systems. Interestingly, many of these biologically active salivary proteins belong to the lipocalin protein family. A proliferation of lipocalin genes has occurred via gene duplication and subsequent divergence. Functional genomic, proteomic, and functional studies have been performed to probe the role of salivary lipocalins in blood feeding. In the course of these investigations, anticoagulant, antiplatelet, antiinflammatory, and vasodilatory molecules have been described. (+info)
Effect of blood components, abdominal distension, and ecdysone therapy on the ultrastructural organization of posterior midgut epithelial cells and perimicrovillar membranes in Rhodnius prolixus.
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The effects of blood components, nerve-cord severance, and ecdysone therapy on the posterior midgut epithelial cells of 5th-instar Rhodnius prolixus nymphs 10 days after feeding were analyzed by transmission electron microscopy. Cutting the nerve-cord of the blood-fed insects partially reduced the development of microvilli and perimicrovillar membranes (PMM), and produced large vacuoles and small electrondense granules; insects fed on Ringer's saline diet exhibited well developed microvilli and low PMM production; swolled rough endoplasmatic reticulum and electrondense granules; Ringer's saline meal with ecdysone led to PMM development, glycogen particles, and several mitochondria in the cytoplasm; epithelial cells of the insects fed on Ringer's saline meal whose nerve-cord was severed showed heterogeneously distributed microvilli with reduced PMM production and a great quantity of mitochondria and glycogen in the cytoplasm; well developed microvilli and PMM were observed in nerve-cord severed insects fed on Ringer's saline meal with ecdysone; Ringer's saline diet containing hemoglobin recovered the release of PMM; and insects fed on human plasma showed slightly reduced PMM production, although the addition of ecdysone in the plasma led to a normal midgut ultrastructural organization. We suggest that the full development of microvilli and PMM in the epithelial cells depends on the abdominal distension in addition to ingestion of hemoglobin, and the release of ecdysone. (+info)
Structural determinants of factor IX(a) binding in nitrophorin 2, a lipocalin inhibitor of the intrinsic coagulation pathway.
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Nitrophorin 2 (NP2) is a salivary lipocalin from Rhodnius prolixus that binds with coagulation factors IX (fIX) and IXa (fIXa). Binding of NP2 with fIXa results in potent inhibition of the intrinsic factor Xase complex. A panel of site-directed surface mutants of NP2 was generated to locate determinants of high affinity fIX(a) binding. The locations of the mutations were based on comparisons with the related, but less potent, inhibitor nitrophorin 3 (NP3). Three point mutants (K21A, K92A, and V94A) were found that clearly reduced the inhibitory potency as measured by the activity of a reconstituted factor Xase system. Binding of NP2 with fIXa and fIX as measured by surface plasmon resonance and isothermal titration calorimetry was reduced in a similar manner. Of the three mutants, two (K92A and V94A) were located on the loop connecting beta-strands E and F of the lipocalin beta-barrel. The largest changes were seen with the K92A mutation, which lies at the apex of the loop, with a smaller effect being seen with mutation of Val(94). Combination of four E-F loop mutations (K92A, A93K, V94A, E97A) in a single mutant reduced the inhibitory potency and binding to levels similar to those seen with NP3 without affecting heme or histamine binding. (+info)
Biological effect of 1-dodecanol in teneral and post-teneral Rhodnius prolixus and Triatoma infestans (Hemiptera: Reduviidae).
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Topical application of 1-dodecanol was significantly more toxic against teneral first nymphs (1-3 h old) than post-teneral first nymphs (24 h old). The lethal dose ratios were 711,500 for Rhodnius prolixus and 3613 for Triatoma infestans. No significative difference between LD50 was found when 1-dodecanol was injected in recently hatched adult R. prolixus (1-4 h old) nor in older adults (24 h old). These values were similar to those calculated for deltamethrin (an effective triatomicide), showing that 1-dodecanol had no insecticidal properties when it was applied by injection. Topical application of high dose of 1-dodecanol (1 microg/i) on teneral first nymphs of R. prolixus, produced an interruption of the darkening process of the cuticle, and probably in the development of its physiological properties. (+info)
Identifying health centers in honduras infested with Rhodnius prolixus using the seroprevalence of Chagas disease in children younger than 13 years.
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The objective of this study is to determine if a Chagas disease protocol starting with a serological survey is as reliable at identifying insect-infested areas as one using the gold standard entomological survey. The study found that health center areas infested with Rhodnius prolixus were identified using a threshold seroprevalence of 0.1%. The serological survey took half the time and was 30% less expensive than the entomological survey. Developing countries with limited resources may find this strategy useful in combating Chagas disease. This strategy also identifies seropositive children, which facilitates their treatment. (+info)