Eva Katona

Kinetics of nerve impulse blocking by protein cross-linking aldehydes Apparent critical thermal points

The effect of formaldehyde, crotonaldehyde, butyraldehyde, glutaraldehyde and cinnamaldehyde on the compound action potential of frog sciatic nerve was studied in the temperature domain 20-35 degrees C at various aldehyde concentrations. All these reagents gradually decrease the amplitude of nerve action potential, up to the complete block, the order of effectiveness being: crotonaldehyde greater than cinnamaldehyde greater than butyraldehyde greater than formaldehyde greater than glutaraldehyde. The effect of cinnamaldehyde is almost completely reversible, while all others have irreversible action. The dependence of the blocking time on temperature and concentration is well expressed in all cases by the same empirical equation. This dependence points to the existence of critical temperatures, specific for each aldehyde, at which impulse blocking would be instantaneous, regardless of concentration. These temperatures (obtained by extrapolation) lie between 43 degrees C (for crotonaldehyde) and 57.5 degrees C (for butyraldehyde). The existence of free amino groups within ionic channels, as main sites of aldehyde attack, is inferred.

Sequential sodium-proton exchange in thrombin-induced human platelets

Thrombin stimulation of human platelets initiates a membrane depolarization attributable to a Na+ influx into, and an alkalinization of, the cytoplasm, both of which follow a similar rapid time scale and thrombin-dose dependence. These responses precede secretion of the contents of the dense granules (serotonin) and, after 1 minute, of lysosomes (beta-glucuronidase). We have evaluated these parameters in the presence of 2H2O in order to determine if the Na+ influx and H+ efflux are sequential or simultaneous. NMR evidence indicates that 2H2O equilibration in rapid, and virtually complete within the 3 min prestimulation platelet equilibration period. In response to an 0.05 U/ml addition of thrombin, the rate of depolarization is 70-80% slower in 2H2O than in H2O. The time to reach maximal depolarization is 5 to 10 seconds longer in 2H2O, the extent of depolarization 60% inhibited, and the pH change 85% inhibited. The serotonin secretion is unaltered, while the beta-glucuronidase secretion is 130-180% enhanced. Dimethylamiloride inhibits the Na+ influx and the pH change completely. These results suggest that the Na+ and H+ fluxes across the plasma membrane are interdependent but neither simultaneous nor electroneutral. Furthermore, granule secretion, previously shown by us to be independent of the existent Na+ gradient, depends on the cytoplasmic K+ and H+ concentrations.

Epigallocatechin 3-O-gallate induces 67 kDa laminin receptor-mediated cell death accompanied by downregulation of ErbB proteins and altered lipid raft clustering in mammary and epidermoid carcinoma cells.

Since the administration of synthetic medicines is associated with drug resistance and undesired side effects, utilization of natural compounds could be an alternative and complementary modality to inhibit or prevent the development of tumors. Epigallocatechin 3-O-gallate (EGCG, 1), the major flavan component of green tea, and genistein (2), a soy isoflavonoid, are known to have chemopreventive and chemotherapeutic effects against cancer. This study demonstrated that both flavonoids inhibit cell proliferation, an effect enhanced under serum-free conditions. Compound 1, but not 2, induced downregulation of ErbB1 and ErbB2 in mammary and epidermoid carcinoma cells, and its inhibitory effect on cell viability was mediated by the 67 kDa laminin receptor (67LR). While 1 was superior in inducing cell death, 2 was more efficient in arresting the tumor cells in the G2/M phase. Furthermore, number and brightness analysis revealed that 1 decreased the homoclustering of a lipid raft marker, glycosylphosphatidylinositol-anchored GFP, and it also reduced the co-localization between lipid rafts and 67LR. The main conclusion made is that the primary target of 1 may be the lipid raft component of the plasma membrane followed by secondary changes in the expression of ErbB proteins. Compound 2, on the other hand, must have other unidentified targets.

Redox status parameters and PBMC membrane fluidity in diabetes mellitus

Abstract The present study aims at finding correlations between certain biochemical and biophysical blood parameters for diabetes patients, focusing on the antioxidant status of the red blood cells and the membrane fluidity of peripheral blood mononuclear cells (PBMC), the endothelial function and the risk of stable interaction between the leucocytes and the endothelium. For that purpose we evaluated blood samples from 32 diabetes patients compared to a control group of 10 subjects for erythrocytes’ enzymatic activity of glucose-6-phosphate dehydrogenase and of superoxide dismutase, their susceptibility to lipid peroxidation, the plasma nitric oxide stable end products level and the PBMC membrane fluidity. Our results showed that the erythrocytes’ antioxidant mechanisms and the PBMC membrane fluidity are impaired under chronic hyperglycemic conditions. Since microvascular complications of diabetes are mainly determined by redox mechanisms, the evaluation of these parameters might help in characterizing th...