Gating of aquaporins by heavy metals in Allium cepa L. epidermal cells

Changes in the water permeability, aquaporin (AQP) activity, of leaf cells were investigated in response to different heavy metals (Zn2+, Pb2+, Cd2+, Hg2+). The cell pressure probe experiments were performed on onion epidermal cells as a model system. Heavy metal solutions at different concentrations (0.05 μM–2 mM) were used in our experiments. We showed that the investigated metal ions can be arranged in order of decreasing toxicity (expressed as a decrease in water permeability) as follows: Hg>Cd>Pb>Zn. Our results showed that β-mercaptoethanol treatment (10 mM solution) partially reverses the effect of AQP gating. The magnitude of this reverse differed depending on the metal and its concentration. The time course studies of the process showed that the gating of AQPs occurred within the first 10 min after the application of a metal. We also showed that after 20–40 min from the onset of metal treatment, the water flow through AQPs stabilized and remained constant. We observed that irrespective of the metal applied, the effect of AQP gating can be recorded within the first 10 min after the administration of metal ions. More generally, our results indicate that the toxic effects of investigated metal ions on the cellular level may involve AQP gating

THERMAL-STABILITY OF DIOCTADECYLDIMETHYLAMMONIUM BROMIDE (DOAB) VESICLES IN AQUEOUS-SOLUTIONS CONTAINING HEXADECYLTRIMETHYLAMMONIUM BROMIDE (CTAB)

When hexadecyltrimethylammonium bromide (CTAB) is added to dioctadecyldimethylammonium bromide (DOAB) vesicles in aqueous solutions, the gel to liquid crystal transition temperature is unaffected in the first scan of a differential scanning microcalorimeter. Subsequent scans are more complicated indicating that monomeric CTAB can penetrate the DOAB vesicles when the latter are in the liquid crystalline form

PHASE-TRANSITIONS IN THE BILAYERS OF VESICLES FORMED FROM BINARY-MIXTURES OF SYMMETRICAL DI-N-ALKYLPHOSPHATES IN AQUEOUS-SOLUTIONS

Vesicles in aqueous solutions were prepared from binary equimolar mixtures of di-n-alkyl-phosphates (sodium and potassium), (R(1)O)(2)PO(2)(-)M(+) and (R(2)O)(2)PO(2)(-)M(+). When the number of carbon atoms in R(1) and R(2) differs by two and when R(1) or R(2) = C12H25, C14H29, C16H33 and C18H37 the membranes undergo well defined gel to liquid crystal transitions at characteristic temperatures T-m. The recorded TmS are intermediate between the melting temperatures for vesicles prepared from the respective single di-n-alkylphosphates. Furthermore, the extrema recorded by differential scanning microcalorimetry show that the vesicle membrane is made up of domains that differ in composition. For those vesicles produced from di-n-alkylphosphates where the number of carbon atoms in R(1) and R(2) differs by more than two the plots recorded by the scanning microcalorimeter are complex. The scans show many extrema, suggesting that the bilayers are formed from many domains having different compositions. In all cases, the scan patterns are essentially repeated through several heat-cool-heat...cycles. The temperatures T-m are increased relative to those of the component surfactants when K+ and Na+ salts are mixed, showing that the counter cations play an important role in determining the thermotropic properties of the vesicles reflecting the importance of electrical interactions in determining the packing within the bilayers.</p