Mechanisms of ouabain toxicity.
The suggested involvement of ouabain in hypertension raised the need for a better understanding of its cellular action, but the mechanisms of ouabain toxicity are only now being uncovered. In the present study, we show that reduced glutathione (GSH) protected ouabain-sensitive (OS) cells from ouabain-induced toxicity and that the inhibition of GSH synthesis by D, L-buthionine-(S,R)-sulfoximine (BSO) sensitized ouabain-resistant (OR) cells. We could not observe formation of *OH or H2O2, but there was an increase in O2*-only in OS cells. Unexpectedly, an increased number of OR cells depolarized after treatment with ouabain, and BSO blocked this depolarization. Moreover, GSH increased ouabain-induced depolarization in OS cells. A sustained increase in tyrosine phosphorylation (P-Tyr) and Ras expression was observed after treatment of OS cells, and GSH prevented it. Conversely, BSO induced P-Tyr and Ras expression in ouabain-treated OR cells. The results obtained have three major implications: There is no direct correlation between membrane depolarization and ouabain-induced cell death; ouabain toxicity is not directly related to its classical action as a Na+, K+-ATPase inhibitor but seems to be associated to signal transduction, and GSH plays a major role in preventing ouabain-induced cell death.
Valente
Raphael C
RC
Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro (UFRJ), Brazil.
Capella
Luiz S
LS
Monteiro
Robson Q
RQ
Rumjanek
Vivian M
VM
Lopes
Aníbal G
AG
Capella
Márcia A M
MA
D000818:Animals; D016923:Cell Death; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005978:Glutathione / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D010042:Ouabain / Q000633:toxicity*; D010766:Phosphorylation; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D013481:Superoxides; D014443:Tyrosine; D010042:Ouabain; D016283:Proto-Oncogene Proteins p21(ras); D005978:Glutathione