title: Na-nitroprusside and HgCl2 modify the water permeability and volume of human erythrocytes.
abstract: The passage of water through the aquaporin-1 (AQP1) transmembrane channel protein of the human erythrocyte is known to be inhibited by organic mercurials such as p-chloromercuribenzoate (pCMB), which react with the free SH-group of the critical cysteine (Cys189) located near the constriction of the AQP1 water-specific channel. Sodium nitroprusside (SNP), which is known as a nitric oxide (NO) donor in interactions with SH-containing molecules, is shown here to suppress the diffusional water permeability (P(d)) of the erythrocyte membrane, presumably as a result of reaction with the Cys189 of the human erythrocyte AQP1 water channels. Further, treatment of erythrocytes with HgCl(2) is found to result in a cell volume decrease that can be related to activation of membrane K(+)-selective Gárdos channels and subsequent loss of intracellular K(+) and cell shrinkage. The variations in P(d) and volume of the erythrocyte were deduced from induced variations in the measured proton ((1)H) nuclear magnetic resonance (NMR) transverse (T(2)) relaxation functions of water exchanging between diamagnetic intracellular and paramagnetic extracellular compartments of the 20-25% hematocrit samples. The extracellular solvent contained 10 mM membrane-impermeable paramagnetic Mn(2+) ions. The (1)H-T(2) NMR technique allows determination of the time constant tau(exch) (for exchange of the erythrocyte intracellular water) that is inversely proportional to the permeability coefficient P(d) when the intracellular water volume is left unmodified, as in the case of SNP-treated erythrocytes. However, for HgCl(2)-treated erythrocytes, this technique showed simultaneous variation of both tau(exch) and the volume ratio V(in)/V(out) of intracellular and extracellular water in proportions suggesting that P(d) was left unmodified. The HgCl(2) effect has been found to be partly reversible by the reducing activity of added mercaptoethanol.
authors.affiliation: Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia. gojmir.lahajnar@fmf.uni-lj.si <gojmir.lahajnar@fmf.uni-lj.si>
authors.forename: Gojmir
authors.initials: G
authors.lastname: Lahajnar
authors.forename: Slavko
authors.initials: S
authors.lastname: Pecar
authors.forename: Ana
authors.initials: A
authors.lastname: Sepe
mesh_terms: D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000502:physiology*; D004912:Erythrocytes / Q000187:drug effects / Q000502:physiology; D008627:Mercuric Chloride / Q000008:administration & dosage*; D009599:Nitroprusside / Q000008:administration & dosage*; D014867:Water / Q000378:metabolism*
chemical_list: D004338:Drug Combinations; D014867:Water; D009599:Nitroprusside; D008627:Mercuric Chloride