Adaptive Evolution of the Venom-Targeted vWF Protein in Opossums that Eat Pitvipers

The rapid evolution of venom toxin genes is often explained as the result of a biochemical arms race between venomous animals and their prey. However, it is not clear that an arms race analogy is appropriate in this context because there is no published evidence for rapid evolution in genes that might confer toxin resistance among routinely envenomed species. Here we report such evidence from an unusual predator-prey relationship between opossums (Marsupialia: Didelphidae) and pitvipers (Serpentes: Crotalinae). In particular, we found high ratios of replacement to silent substitutions in the gene encoding von Willebrand Factor (vWF), a venom-targeted hemostatic blood protein, in a clade of opossums known to eat pitvipers and to be resistant to their hemorrhagic venom. Observed amino-acid substitutions in venom-resistant opossums include changes in net charge and hydrophobicity that are hypothesized to weaken the bond between vWF and one of its toxic snake-venom ligands, the C-type lectin-like protein botrocetin. Our results provide the first example of rapid adaptive evolution in any venom-targeted molecule, and they support the notion that an evolutionary arms race might be driving the rapid evolution of snake venoms. However, in the arms race implied by our results, venomous snakes are prey, and their venom has a correspondingly defensive function in addition to its usual trophic role

Ação inibidora do gás carbonico sobre as convulsões experimentais: III) experiências na crioepilepsia da rã: mecanismo da ação inibidora do gás carbonico nas convulsões

Neste trabalho descrevemos experiencias destinadas a mostrar a influência do pH nas crises convulsivas por resfriamento da medula espinhal da rã e estudar o mecanismo da ação inibidora do gás carbonico sobre estas conculsões. Verificamos que o CO² não age atravez um abaixamento do pH do sangue ou do meio intercelular. O gás carbonico teria uma ação específica que estaria ligada á sua grande difusibilidade. Essa sua propriedade permitiria que penetrasse ràpidamente no interior de neurônio, abaixando sensìvelmente o pH intracelular, sem que houvesse nítida variação do pH do sangue.In this work described experiments to show the influence of the pH on convulsions caused by cooling the spinal cord of frogs, and to study the mechanism of the inhibitory action of carbon dioxide on these convulsions. We found that carbon dioxide does not act by lowering the pH of the blood or intercellular medium. Carbon dioxide would have a specific action which would be connected with its great diffusibility. This property would enable it to penetrate rapidly into the interior of the neurone, appreciably lowering the intracellular pH, in the absence of a clear variation in the pH of the blood

Factors underlying the natural resistance of animals against snake venoms

The existence of mammals and reptilia with a natural resistance to snake venoms is known since a long time. This fact has been subjected to the study by several research workers. Our experiments showed us that in the marsupial Didelphis marsupialis, a mammal highly resistant to the venom of Bothrops jararaca, and other Bothrops venoms, has a genetically origin protein, a alpha-1, acid glycoprotein, now highly purified, with protective action in mice against the jararaca snake venom