Chini EN, de Faria FO, Cardoso CM, de Meis L. The enhancement of Ca2+ efflux from sarcoplasmic reticulum vesicles by urea.
Arch Biochem Biophys 1992;
299:73-6. [PMID:
1280064 DOI:
10.1016/0003-9861(92)90245-r]
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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(beta-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 (Ca(2+)-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.
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