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Organic osmolytes betaine, sorbitol and inositol are potent inhibitors of erythrocyte membrane ATPases.

Moeckel, Gilbert W; Shadman, Ramin; Fogel, Joy M; Sadrzadeh, Sayed M H.
Life Sci; 71(20): 2413-24, 2002 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-12231402
Organic osmolytes are used in animal and plant cells to adapt to hyper- and hypoosmolar stress. We used our RBC-membrane model to investigate the effects of the osmolytes betaine, sorbitol and myo-inositol on Na(+)/K(+)-ATPase, Ca(2+)-ATPase and calmodulin-stimulated Ca(2+)-ATPase (CaM). Our results show that betaine inhibited ATPases by more than 61%: Na(+)/K(+)-ATPase (75 +/- 5.9 vs 27 +/- 2.2), Ca(2+)-ATPase (236 +/- 18.9 vs 62 +/- 4.9), and CaM (450 +/- 18 vs 174 +/- 6.9) (microM pi/min/mg protein, control (0 microM betaine) vs 100 micromol/L betaine). Sorbitol (100 micromol/L) inhibited the Ca(2+)-ATPases by 41% (126 +/- 7.6 vs 74 +/- 4.4) and CaM by 42% (253 +/- 17.7 vs 147 +/- 10.3). Inositol (100 micromol/L) inhibited Na(+)/K(+)-ATPase strongest (37 +/- 1.9 vs 20 +/- 1.0; 47% inhibition) while it showed a lesser effect on the Ca(2+)-ATPases (136 +/- 6.8 vs 102 +/- 5.1; 25% inhibition). All osmolytes inhibited RBC membrane ATPases at concentrations above 50 micromol/L, which corresponds to high normal physiologic range for organic osmolytes in serum. Furthermore, the presence of osmolytes (250 micromol/L) decreased hypoosmotic stress induced hemolysis by 42%. Together these data indicate an important regulatory role of organic osmolytes on human RBC membrane ATPases and a protective function of osmolytes in RBCs against hypoosmotic stress.
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