The enhancement of Ca2+ efflux from sarcoplasmic reticulum vesicles by urea

Eduardo Nunes Chini, Felipe Oliveira de Faria, Cristiana M. Cardoso, Leopoldo de Meis

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Abstract

Urea, in nondenaturing concentrations, inhibited Ca2+ uptake by sarcoplasmic reticulum vesicles with no concomitant effect on ATP hydrolysis. This inhibition was antagonized by 5 mm oxalate and 20 mm orthophosphate. At concentrations of 0.2 to 1.0 m, urea induced an increase in the Ca2+ efflux from preloaded vesicles diluted in a medium at pH 7.0 containing 2 mm ethylene glycol bis(β-aminoethyl ether)N,N′-tetraacetic acid, 0.1 mm orthophosphate, and 0.1 mm MgCl2. The urea-induced efflux was arrested by ligands of the (Ca2+-Mg2+) ATPase, namely, K+, Mg2+, Ca2+, and ADP, and by ruthenium red and the polyamines spermine, spermidine, and putrescine. In the case of polyamines a dissociation between the effect on the efflux and the net Ca2+ uptake was observed, as only the efflux could be blocked by the drugs. Glycine betaine, trimethylamine-N-oxide, and sucrose antagonized the effects of urea on both the net Ca2+ uptake and the rate of Ca2+ efflux.

Original languageEnglish (US)
Pages (from-to)73-76
Number of pages4
JournalArchives of Biochemistry and Biophysics
Volume299
Issue number1
DOIs
StatePublished - Nov 15 1992

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ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

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