Chini E N, de Faria F O, Cardoso C M, de Meis L
Departamento de Bioquímica, Universidade Federal do Rio de Janeiro, Brazil.
Arch Biochem Biophys. 1992 Nov 15;299(1):73-6. doi: 10.1016/0003-9861(92)90245-r.
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.
在非变性浓度下，尿素抑制肌浆网囊泡对Ca2+的摄取，同时对ATP水解没有影响。这种抑制作用可被5 mM草酸盐和20 mM正磷酸盐拮抗。在0.2至1.0 M的浓度下，尿素会使预加载的囊泡在含有2 mM乙二醇双（β-氨基乙醚）N，N'-四乙酸、0.1 mM正磷酸盐和0.1 mM MgCl2的pH 7.0培养基中稀释时Ca2+外流增加。尿素诱导的外流被（Ca(2 +)-Mg2 +）ATP酶的配体，即K+、Mg2+、Ca2+和ADP，以及钌红和多胺精胺、亚精胺和腐胺所阻止。就多胺而言，观察到其对外流和净Ca2+摄取的影响之间存在解离，因为只有外流可被药物阻断。甜菜碱、三甲胺-N-氧化物和蔗糖拮抗尿素对净Ca2+摄取和Ca2+外流速率的影响。
