RESUMO
Several partial reactions of the Na(+)-K+ pump enzyme were studied in a microsomal fraction derived from the gill of carp (Cyprinus carpio Linneo). We tested the effect of three toxins [(i) microcystin-LR, (ii) microcystin-LR-like toxin component isolated from Microcystis aeruginosa culture and (iii) okadaic acid] on the phosphorylation, ouabain binding and ATPase activity of the Na(+)-K+ pump. The K(+)-dependent hydrolysis of the Na(+)-dependent phosphorylation of Na(+)-K+ pump, as well the release of bound ouabain were inactivated in direct proportion to the amount of each toxin treatment. These results indicate that these toxins not only block the hydrolysis of phosphorylated protein at serine and threonine residues, but also inhibit the aspartic dephosphorylation step of the sodium pump enzymes. This inactivation could disrupt the ion homeostasis of the internal medium by blocking the gill function. The blockage of gill activity could be the cause of the massive fish death during blooms of M. aeruginosa.
Assuntos
Inibidores Enzimáticos/toxicidade , Brânquias/efeitos dos fármacos , Peptídeos Cíclicos/toxicidade , Fosfoproteínas Fosfatases/antagonistas & inibidores , ATPase Trocadora de Sódio-Potássio/efeitos dos fármacos , Animais , Ligação Competitiva , Carpas , Células Cultivadas , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/metabolismo , Inibidores Enzimáticos/farmacologia , Brânquias/enzimologia , Hidrólise , Indicadores e Reagentes/metabolismo , Toxinas Marinhas , Microcistinas , Microssomos/efeitos dos fármacos , Microssomos/enzimologia , Nitrofenóis/metabolismo , Octoxinol/química , Ácido Okadáico/farmacologia , Compostos Organofosforados/metabolismo , Ouabaína/metabolismo , Ouabaína/farmacologia , Fosforilação/efeitos dos fármacos , ATPase Trocadora de Sódio-Potássio/metabolismoRESUMO
A microsomal fraction enriched in ion pump enzymes was isolated from the gill of the carp (Cyprinus carpio Linneo). Mg(2+)-dependent (Na+ + K+), Na+, HCO3- and Ca(2+)-stimulated ATPase activities were studied following treatment with microcystin-LR-like toxin, the major toxic component isolated from Microcystis aeruginosa culture. These enzyme activities were inhibited in a dose-dependent manner. The maximum inhibition of each enzyme, induced with nM concentration of the toxin, was similar to that produced by inhibitors specific for each ATPase activity. The Mg(2+)-ATPase activity and non-specific hydrolysis of ATP were unaffected. These results strongly suggest that the massive fish death during M. aeruginosa blooms may result from the loss of ion homeostatic processes produced by the inhibitory action of microcystin on the ion pumps of gill chloride cells.
Assuntos
Toxinas Bacterianas/farmacologia , Brânquias/enzimologia , Bombas de Íon/efeitos dos fármacos , Microcystis/química , Animais , ATPases Transportadoras de Cálcio/metabolismo , Carpas , Brânquias/microbiologia , ATPase Trocadora de Sódio-Potássio/metabolismoRESUMO
Four hundred strains of enterobacteria, isolated before the introduction of trimethoprim as a single agent in Chile, were studied. One hundred and thirty six strains (34%) were resistant to greater than or equal to 8 mg/l of trimethoprim and 118 of these (87%) were also resistant to sulphamethoxazole (156 mg/l). Plasmids were detected in 79% of the trimethoprim-resistant strains; 56% of the strains carried two or more plasmids. Trimethoprim resistance could be transferred by conjugation in 66% of the plasmid-carrying strains; this resistance was co-transferred with a variety of other antibiotic resistance determinants.