The effect of the anticancer drugs tamoxifen and hydroxytamoxifen on the calcium pump of isolated sarcoplasmic reticulum vesicles

Toxicology in Vitro : an International Journal Published in Association with BIBRA
J B CustódioV M Madeira

Abstract

The interactions of tamoxifen (TAM) and its active metabolite 4-hydroxytamoxifen (OHTAM) with the sarcoplasmic reticulum (SR) Ca(2+)-pump were investigated. The turnover of the Ca(2+)-ATPase is strongly inhibited by both drugs at low concentrations that do not significantly perturb the lipid organization of SR membranes. Moreover, TAM decreases Ca(2+) accumulation by SR Ca(2+)-ATPase and increases in parallel the ATP hydrolysis, decreasing the energetic efficiency of the Ca(2+)-pump (Ca (2+)ATP coupling ratio) by about 70% at 30 muM. This uncoupling of ATP hydrolysis from Ca(2+) accumulation is a putative consequence of structural defects induced on membranes, since the ATP hydrolysis at low residual Ca(2+) (Ca(2+) not supplemented) is also stimulated. On the other hand, OHTAM decreases the Ca(2+) uptake to a greater extent than TAM but, unlike TAM, it inhibits ATP hydrolysis. Thus, the Ca (2+)ATP ratio is decreased by about 47% at 30 muM OHTAM; this effect is not a consequence of membrane disruption, since the ATP-splitting activity decreases in parallel to Ca(2+) accumulation and no significant effect is detected for ATP hydrolysis at low residual Ca(2+). The inhibition of the Ca(2+)-pump by OHTAM is putatively related to a d...Continue Reading

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Citations

Nov 8, 2001·Toxicology in Vitro : an International Journal Published in Association with BIBRA·M M Cruz SilvaJ B Custódio
Nov 6, 2003·Toxicology in Vitro : an International Journal Published in Association with BIBRA·J P MonteiroV M C Madeira
Nov 6, 2003·Toxicology in Vitro : an International Journal Published in Association with BIBRA·C LuxoM T Silva
Mar 27, 2001·British Journal of Pharmacology·M L DoddsG J Kargacin
Mar 21, 2012·Photochemistry and Photobiology·Theodossis Athanassios TheodossiouJohn Stephen Hothersall
Nov 17, 2015·ACS Chemical Biology·Theodossis Athanassios TheodossiouKristian Berg
Jun 9, 2004·Biochemical Pharmacology·Paula I MoreiraMaria S Santos
Oct 17, 1998·Toxicology and Applied Pharmacology·J B CustodioK B Wallace
Jun 3, 2014·Toxicology·Mariana P C RibeiroJosé B A Custódio
May 17, 2011·Chemico-biological Interactions·Carla Brugin MarekAdelar Bracht
Mar 8, 2000·Biochimica Et Biophysica Acta·M M Cruz SilvaJ B Custódio
Aug 15, 2014·Journal of Cachexia, Sarcopenia and Muscle·Josep M ArgilésSílvia Busquets
Apr 19, 2003·American Journal of Physiology. Heart and Circulatory Physiology·Jianying HeChristopher A Ward

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