RESUMO
The FMRF-amide-activated sodium channel (FaNaC), a member of the ENaC/Degenerin family, is a homotetramer, each subunit containing two transmembrane segments. We changed independently every residue of the first transmembrane segment (TM1) into a cysteine and tested each position's accessibility to the cysteine covalent reagents MTSET and MTSES. Eleven mutants were accessible to the cationic MTSET, showing that TM1 faces the ion translocation pathway. This was confirmed by the accessibility of cysteines present in the acid-sensing ion channels and other mutations introduced in FaNaC TM1. Modification of accessibilities for positions 69, 71 and 72 in the open state shows that the gating mechanism consists of the opening of a constriction close to the intracellular side. The anionic MTSES did not penetrate into the channel, indicating the presence of a charge selectivity filter in the outer vestibule. Furthermore, amiloride inhibition resulted in the channel occlusion in the middle of the pore. Summarizing, the ionic pore of FaNaC includes a large aqueous cavity, with a charge selectivity filter in the outer vestibule and the gate close to the interior.
Assuntos
FMRFamida/farmacologia , Ativação do Canal Iônico/efeitos dos fármacos , Transporte de Íons/efeitos dos fármacos , Canais de Sódio/química , Sódio/metabolismo , Sequência de Aminoácidos , Substituição de Aminoácidos , Animais , Linhagem Celular , Cisteína/química , DNA Complementar/genética , Feminino , Humanos , Mesilatos/farmacologia , Modelos Moleculares , Dados de Sequência Molecular , Família Multigênica , Mutagênese Sítio-Dirigida , Oócitos , Conformação Proteica , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/metabolismo , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Canais de Sódio/efeitos dos fármacos , Canais de Sódio/metabolismo , Eletricidade Estática , Reagentes de Sulfidrila/farmacologia , Xenopus laevisRESUMO
Two cases of moderate neutropenia and 3 cases of severe neutropenia in the course of fusidic acid treatment for sepsis related to a hip prothesis or septic osteitis are reported. Neutropenia was always observed following routine blood cell count, after a mean of 21 days' treatment (16 to 27 days). Moderate fever was observed only once, in a patient with profound neutropenia. A complete recovery of blood cell count was noted in all cases, 5 to 9 days upon discontinuation of fusidic acid. A sternal bone-marrow aspiration was performed in 4 cases, showing normocellularity or hypercellularity in two cases, and moderate hypoplasia of granulocytic cells. The respective roles of other treatments are discussed. Overall, these five cases suggest that reversible granulocytopenia can be caused by protracted treatment with fusidic acid. Although nine different associated drugs could also have been involved in four patients, the causal relationship was less suggestive for three of them due to chronological events. In other cases, the drugs never or very rarely caused neutropenia. Finally, the possibility of vancomycin-induced neutropenia cannot be excluded in one case.
