Inhibition of glucose transport in human erythrocytes by benzylalcohol

Urea and ethylene glycol-facilitated transport systems in the human red cell membrane. Saturation, competition, and asymmetry

The equilibrium exchange of [14C]urea and ethylene glycol was measured using a new type of fast flow system. Approximately equal volumes of saline and air were mixed to form a segmented fluid stream into which 14C-loaded red cells are injected. The stream flows through three filter chambers which allow sampling of the 14C in the extracellular fluid at three time points. The chambers are designed so that they do not disrupt the segmented bubble pattern. The alternating air and saline segments prevent laminar dispersion in the flowing stream and ensure good mixing at the injection and sampling sites. The equilibrium exchange of both urea and ethylene glycol showed saturation kinetics. The maximum permeability (Po) measured in the limit of zero solute concentration is 1.6 X 10(-3) cm/s for urea and 4.8 X 10(-4) cm/s for ethylene glycol (T = 23 degrees C). The apparent dissociation constant (Km) was 218 mM for urea and 175 mM for ethylene glycol. The Po for thiourea is 2.3 X 10(-6) cm/s and the Km is 19 mM. Urea and thiourea inhibit the transport of each other and the inhibition constant (KI) is approximately equal to the Km for both compounds. 53 other analogues of urea were screened for their inhibition of urea or thiourea transport. Several analogues [e.g., 1-(3,4-dichloro-phenyl)-2-thiourea] had a KI in the range of 0.03 mM. The affinity of the inhibitor increased as it was made more hydrophobic. The urea analogues did not significantly inhibit the ethylene glycol or osmotic permeability. Glycerol inhibited ethylene glycol permeability with a KI of 1,200 mM.

Alcohols inhibit adipocyte basal and insulin-stimulated glucose uptake and increase the membrane lipid fluidity

Benzyl alcohol and ethanol, at aqueous concentrations that cause local anesthesia of rat sciatic nerve, affect structural and functional properties of rat adipocytes. The data strongly suggest that structurally-intact membrane lipids are required for the proper cellular uptake of glucose and for the physiologic response of adipocytes to insulin. The structure of adipocyte membrane lipids was examined with the spin label method. Isolated adipocyte 'ghost' membranes were labeled with the 5-nitroxide stearate spin probe I(12,3). Order parameters that are sensitive to the fluidity of the lipid environment of the incorporated probe were calculated from ESR spectra of labeled membranes. Benzyl alcohol and ethanol dramatically increased the fluidity of the adipocyte ghost membrane, as indicated by decreases in the polarity-corrected order parameter S. This concentration-dependent fluidization commenced at approx. 10 mM benzyl alcohol and progressively increased at all higher concentrations tested (up to 107 mM). S decreased approx. 5.7% at 40 mM benzyl alcohol, a change in S comparable in magnitude to that induced by a 6 degrees C increase in the incubation temperature. Benzyl alcohol and ethanol inhibited basal glucose uptake in adipocytes and uptake maximally stimulated by insulin. Temperature-induced increases in membrane fluidity, detected with I(12,3), that closely paralleled the fluidity effects of alcohols were associated only with increases in basal and insulin-stimulated glucose uptake. The contention that the membrane lipid fluidity plays a role in insulin action needs further study.

Toxicology investigations with cell culture systems

This review concerns some of the cell culture systems that are most frequently used in toxicology investigations. In particular, it sets out to evaluate the effectiveness of these cell culture systems in assessing the toxic potential of chemicals. Metabolic studies and general and specific toxicology investigations are highlighted. Specific toxicology investigations relate to the effects of the tests substances on the highly specialized functions typical of the cell systems chosen. The general toxicology investigations include most of the other studies where differentiated or undifferentiated cells have been used to evaluate the effects of the tested substances on common basic biochemical processes essential for life. Lastly, we have attempted to focus attention on the most promising applications of cell cultures in toxicology studies for the near future and to identify those areas where further research is needed. Because of the several excellent reviews that already exist, we have decided not to consider cell cultures utilized in screening potential mutagens and carcinogens. We have also excluded investigations of drug therapeutic effects and action mechanisms of drugs.