Biomedical subjects
Publications and source records attributed to L Lacko.
Diethylpyrocarbonate largely diminished both discontinuities in red cell glucose transport and also in red cell membrane ANS fluorescence at about 17--20 degrees C.
The homologous compounds of the 4-alkoxy- and 4-alkylamino-series inhibit the exchange transport of glucose in human erythrocytes; they show a competitive inhibition with one or two inhibitor molecules which become bound to a singular site of the transport system for glucose. The importance of length of hydrocarbon chain of the localanesthetics for the mode of their action is discussed.
The effect of D-, L- and DL-propranolol on the glucose uptake in human erythrocytes was studied. It was observed that all three compounds competitively inhibit the glucose transport and have identical inhibition constants. The pH dependence of the inhibition constant indicates that uncharged propranolol is a more potent inhibitor than the charged one. The thermodynamic parameters of the interaction of propranolol with the glucose transport system were determined and discussed.
The inhibition of glucose transport by the non-ionizable local-anesthetic denzylalcohol is of the mixed type and independent of pH. The affinity of benzylalcohol to the free carrier is about three times larger than that to the carrier-glucose complex.
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The thermodynamic parameters deltaH degrees, deltaF degrees, deltaS degrees and the pH dependence of the interaction between steroids and the glucose carrier in human erythrocytes have been studied. The results indicate that, according to the structure of the steroids, hydrophilic as well as hydrophobic bonds can be involved in the association. For the binding of the C-21-steroids to the carrier the polarity rule has been observed to be valid. On the basis of the thermodynamic parameters it has been found that in the association process of the steroids with the carrier, simultaneous randomization of ordered water molecules is important.
Local anesthetics inhibit the exhange transport of glucose in human erythroytes. All compounds tested showed a competitive inhibition except lidocaine and baycaine causing a non-competitive one. Moreover the transport system can bind two inhibitor molecules to one transport site as described for tetracaine and oxybuprocaine.
Steroids inhibit the exchange transport of glucose in human erythrocytes. The extent of inhibition is roughly correlated to the affinity of the steroids to the membrane lipids. All C-21-steroids tested show a competitive inhibition while the C-19-steriods show different types of inhibition. 5Beta-androstane-3,17-dione acts as a competitive inhibitor. The inhibition by testosterone is of mixed type, while with androst-4-ene-3,17-dione and 5alpha-androstane-3,17-dione a non-competitive inhibition is observed. In this case two inhibitor molecules can be bound per transport molecule. The "non-competitive" inhibitors compete also to some extent with the glucose binding. This effect, however, is at high inhibitor concentrations masked by the more powerful non-competitive inhibition. Competitive and non-competitive inhibitors compete with each other. The structural requirements for the different types of inhibition are discussed.