Adaptive evolution of the vertebrate skeletal muscle sodium channel

Tetrodotoxin (TTX) is a highly potent neurotoxin that blocks the action potential by selectively binding to voltage-gated sodium channels (Nav). The skeletal muscle Nav (Nav1.4) channels in most pufferfish species and certain North American garter snakes are resistant to TTX, whereas in most mammals they are TTX-sensitive. It still remains unclear as to whether the difference in this sensitivity among the various vertebrate species can be associated with adaptive evolution. In this study, we investigated the adaptive evolution of the vertebrate Nav1.4 channels. By means of the CODEML program of the PAML 4.3 package, the lineages of both garter snakes and pufferfishes were denoted to be under positive selection. The positively selected sites identified in the p-loop regions indicated their involvement in Nav1.4 channel sensitivity to TTX. Most of these sites were located in the intracellular regions of the Nav1.4 channel, thereby implying the possible association of these regions with the regulation of voltage-sensor movement

Origem e distribuição do plexo braquial de Saimiri sciureus

Os autores descreveram a origem e composição do plexo braquial de quatro Saimiri sciureus, pertencentes ao Centro Nacional de Primatas (Cenp), Ananindeua/PA, os quais foram fixados com formaldeído e dissecados. Os achados revelaram que o plexo braquial desta espécie é constituído por fibras neurais provenientes da união das raízes dorsais e ventrais das vértebras cervicais C4 a C8 e torácica T1, e organizado em quatro troncos. Cada tronco formou um nervo ou um grupo de nervos, cuja origem variou entre os animais; na maioria, foi encontrado o tronco cranial originando o nervo subclávio, o tronco médio-cranial dando origem aos nervos supraescapular, subescapular, parte do radial, e em alguns casos ao nervo axilar, nervo musculocutâneo e ao nervo mediano; o tronco médio-caudal formou parte do nervo radial, e em alguns casos os nervos axilar, nervo musculocutâneo, nervo mediano, nervo toracodorsal, nervo ulnar e nervo cutâneo medial do antebraço, sendo os dois últimos também originados no tronco caudal

Site of Action and Active Form of Aminopyridines in Squid Axon Membranes1

ABSTRACT ABBREVIATiONS: AP, aminopyridine; DAP, diaminopyrkline; ASW, artificial sea water; 4-APMI, 4-aminopyridine methkxlkle; TEA, tetraeth 1ammon-ium

3,4-diaminopyridine. A potent new potassium channel blocker.

3,4-diaminopyridine has been found to act very potently in selectively blocking the potassium channels of squid axon membranes. The apparent dissociation constants for this action are estimated to be 5.8 micron and 0.7 micron for external and internal applications, respectively, the potency being about 50 times higher than that of 4-aminopyridine. The block depends upon the membrane potential, time, and stimulus frequency. 3,4-diaminopyridine shows great promise as a useful tool for the study of membrane ionic channels