| Abstrakt: |
S-nitrosoglutathione (GSNO) is an endogenous S-nitrosylated glutathione derivative (GSH) involved in NO signaling. GSNO acts as a carrier of nitrosyl groups to cysteine (both free amino acid and its residues in proteins), a glutathionylation agent, and an NO donor. We investigated the effects of GSNO, GSH, and oxidized glutathione (GSSG) on the activity of two main ion pumps of the plasma membrane, Na+/K+-ATPase (NKA) and plasma membrane Ca2+-ATPase (PMCA). Plasma membranes were obtained from the rat cerebral cortex by differential centrifugation. Preincubation of the saponinpermeabilized plasma membranes at 37°C (but not at 0°C) with various concentrations of GSNO led to partial inhibition of ATPase activities of NKA and PMCA (on average, by 19.4 ± 2.2 and 42.1 ± 3% at 10 mM GSNO, respectively). The addition of GSH instead of GSNO did not affect the enzyme activities, while GSSG inhibited these enzymes much weaker than GSNO. The inhibited enzyme activities after the action of GSNO were partially restored after incubation of the membranes with a thiol-reducing agent, 2-mercaptoethanol. GSNO-dependent inhibition of NKA was not observed in the presence of ouabain (>1.0 μM), when only isozymes having an α1-subunit were active. GSNO inhibited both high- and lowsensitive to Ca2+ (calmodulin-dependent and calmodulin-independent) PMCA activities by 51 and 33%, respectively, with no changes in Km for Ca2+. It is assumed that GSNO or its degradation product(s), by modifying the thiol groups in NKA and PMCA molecules, partly inhibit their activity. Only NKA isozymes with α2 and α3 subunits, which are highly sensitive to ouabain, are likely to manifest such sensitivity. Inhibition of PMCA is not associated with a change in its sensitivity to Ca2+. [ABSTRACT FROM AUTHOR] |
