The imaging properties and sensitivity of the facial pits of pitvipers as determined by optical and heat-transfer analysis.
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It is commonly assumed that the facial pit of pitvipers forms relatively sharp images and can detect small differences in environmental surface temperatures. We have visualized the temperature contrast images formed on the facial pit membrane using a detailed optical and heat transfer analysis, which includes heat transfer through the air in the pit chambers as well as via thermal infrared radiation. We find the image on the membrane to be poorly focused and of very low temperature contrast. Heat flow through the air in the pit chambers severely limits sensitivity, particularly for small animals with small facial pit chambers. The aperture of the facial pit appears to be larger than is optimal for detecting small targets such as prey at 0.5 m. Angular resolution (i.e. sharpness) and image strength and contrast vary complexly with the size of the pit opening. As a result, the patterns of natural background temperatures obscure prey items and other environmental features, creating false patterns. Consequently, snakes cannot simply target the strongest signal to strike prey. To account for observed behavioral capabilities, the sensory endings on the pit membrane apparently must respond to temperature contrasts of 0.001 degrees C or less. While neural image sharpening likely enhances imaging performance, it appears important for foraging snakes to select ambush sites offering uniform backgrounds and strong thermal contrasts. As the ancestral facial pit was likely less sensitive than the current organ, objects with strong thermal signals, such as habitat features, were needed to drive the evolution of this remarkable sense. (+info)
Purification and partial characterizations of coagulant protein FIa from Daboia russelli siamensis (Myanmar) venom.
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AIM: To purify and characterize the coagulant protein FIa from Daboia russelli siamensis (Myanmar) venom. METHODS: FIa was purified from Daboia russelli siamensis (Myanmar) venom by ion-exchange chromatography on CM-Sephadex C-50, and gel filtration on Sephadex G-75 and a Superdex 75 column. The hemostatic activity of FIa was determined by the method of Williams and Esnouf. The specific chromogenic substrates were used respectively to determine the activation of factor X and prothrombin. The fibrinogen-clotting activity of FIa was determined by the method of Gao et al. Normal saline was used as a negative control while factor Xa and thrombin were used as positive controls, respectively. RESULTS: FIa, a coagulant protein, was achieved by ion-exchange chromatography and gel filtration with a molecular weight of 34,479 and an isoelectric point of 7.2. FIa was shown to have strong hemostatic activity. The hemostatic activity of 0.5 mg FIa was equal to that of 1.5625 u thrombin. FIa primarily activated factor X, however, had no influence on prothrombin, nor did it cleave or clot fibrinogen. CONCLUSION: FIa is a factor X-activating enzyme, which could activate factor X to factor Xa, but has no effect on prothrombin and fibrinogen. (+info)
Characterization of a human coagulation factor Xa-binding site on Viperidae snake venom phospholipases A2 by affinity binding studies and molecular bioinformatics.
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BACKGROUND: The snake venom group IIA secreted phospholipases A2 (SVPLA2), present in the Viperidae snake family exhibit a wide range of toxic and pharmacological effects. They exert their different functions by catalyzing the hydrolysis of phospholipids (PL) at the membrane/water interface and by highly specific direct binding to: (i) presynaptic membrane-bound or intracellular receptors; (ii) natural PLA2-inhibitors from snake serum; and (iii) coagulation factors present in human blood. RESULTS: Using surface plasmon resonance (SPR) protein-protein interaction measurements and an in vitro biological test of inhibition of prothrombinase activity, we identify a number of Viperidae venom SVPLA2s that inhibit blood coagulation through direct binding to human blood coagulation factor Xa (FXa) via a non-catalytic, PL-independent mechanism. We classify the SVPLA2s in four groups, depending on the strength of their binding. Molecular electrostatic potentials calculated at the surface of 3D homology-modeling models show a correlation with inhibition of prothrombinase activity. In addition, molecular docking simulations between SVPLA2 and FXa guided by the experimental data identify the potential FXa binding site on the SVPLA2s. This site is composed of the following regions: helices A and B, the Ca2+ loop, the helix C-beta-wing loop, and the C-terminal fragment. Some of the SVPLA2 binding site residues belong also to the interfacial binding site (IBS). The interface in FXa involves both, the light and heavy chains. CONCLUSION: We have experimentally identified several strong FXa-binding SVPLA2s that disrupt the function of the coagulation cascade by interacting with FXa by the non-catalytic PL-independent mechanism. By theoretical methods we mapped the interaction sites on both, the SVPLA2s and FXa. Our findings may lead to the design of novel, non-competitive FXa inhibitors. (+info)
Pediatric sex group differences in location of snakebite injuries requiring antivenom therapy.
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OBJECTIVE: The objective of this study is to examine the patterns of snakebite injury in pediatric patients that require antivenom therapy and to evaluate whether and when sex group differences exist. METHODS: We performed a nationwide, multicenter, retrospective evaluation of 24 regional poison centers from 2002 and through 2004 of data for antivenom therapy for Crotaline snakebites. Data points abstracted included the age of the victim, sex of the victim, and location of bite. We calculated contingency tables of the data with statistical significance by Fisher's exact test. RESULTS: We evaluated 204 records that involved pediatric patients; 3 of the patients had no recorded age. In 16 of the records, the bite location was not documented (2 children and 1 unknown age) or was listed as head/neck (1 child). These records were not included in the data analysis. There were bites in 136 males and 65 females. Males were more likely than females to suffer an injury to the upper extremity (56.6% vs. 26.2%; p<0.01). Males were more likely to suffer injuries to the upper extremity in all age groups (p <0.05) except for the group aged 10 through 12 years; in the group aged 10 through 12, we did not see significant differences between the sexes (p=0.729). Males are more likely to suffer an upper extremity bite with increasing age (p=0.029), while females showed no significant change in the location of bites (p=0.223). CONCLUSION: Male children were more likely than female children to suffer Crotaline snakebites that required antivenom therapy. In this population, significant differences between locations of snakebites were found. Males were more likely than females to be bitten in the upper extremities. This difference appears as early as 1 to 4 years of age. (+info)
Clinical aspects and consequences of envenoming by a captive rhinoceros viper (Bitis nasicornis) in Hungary.
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