Mechanisms of ouabain toxicity

ABSTRACT 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 H 2 O 2 , but there was an increase in O 2 •− 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.