Dissociation of human αb-crystallin aggregates by thiocyanate is structurally and functionally reversible

Conformational modifications and changes in the aggregation state of human \u3b1B-crystallin were investigated at different concentrations of SDS, KBr, urea, and NH4SCN and at different temperatures. Intrinsic fluorescence measurements indicated complete and reversible unfolding of the protein at 2 M NH4SCN, whereas the concentration of urea required for complete and irreversible unfolding was 6 M. Gel permeation chromatography indicated almost complete dissociation of the micelle-like aggregate of \u3b1B-crystallin in 2 M NH4SCN, but only partial dissociation into large-sized aggregates in 6 M urea. Thiocyanate-treated \u3b1B-crystallin recovered its chaperone-like activity upon dilution of the dissociating agent, whereas the urea-treated protein did not

The action of taurine on chloride conductance and excitability characteristics of rat striated muscle fibers

Taurine and related compounds were applied to rat extensor digitorum longus muscle fibers in vitro, and the effects on membrane potential, cable parameters, component conductances and excitability were observed with microelectrodes. After 20 min in 60 mM taurine the fibers hyperpolarized and there were decreases in the latency of a rheobasic stimulus, the duration of the action potential and the maximum number of spikes elicited by depolarizing pulses. The effects of taurine on membrane resistance are attributed to a specific dose-dependent increase in membrane chloride conductance (G) with little or no effect on membrane potassium conductance. (Cl)Gamma-aminobutyric acid at 30-60 mM also produced a specific increase in G(Cl) but, unlike taurine it caused a significant depolarization. β-alanine or sucrose at 60 mM did not mimic any of the effects observed with taurine at this concentration. It was concluded that the actions of taurine and GABA on excitability can be explained by increases in G(Cl)

NMDA receptors play an anti-aggregating role in human platelets

Receptors for different monoamines, peptides and other neurohormones are present in the plasma membrane of platelets, and the sophisticated process of haemostasis is regulated by the interplay of their physiologic agonists (1). The recent report of a platelet binding site for phencyclidine (2) suggested a possible role of N-methyl-D-aspartate (NMDA) receptors in platelet function. Isotherms of [3H]-glutamate (GLU), [3H]-CGP-39653, [3H]-glycine (GLY) and [3H]-MK-801 carried out in platelet membranes yielded Bmax and Kd values for these ligands similar to those present in neurons, and NMDA only partially displaced [3H]-GLU. In neurons [3H]-MK-801 binding is potentiated by GLU and/or GLY and, being specific for the open NMDA receptor channel species, it has a functional meaning. In platelet membranes neither GLU and/or GLY increased [3H]-MK-801 binding; thus suggesting that NMDA receptors in platelets are different from those present in neurons. GLU or NMDA alone did not induce platelet aggregation. However, both amino acids were antagonistic on the aggregating activity of arachidonic acid (AA), NMDA being 3 orders of magnitude more active than GLU, and NMDA also antagonized adenosine diphosphate (ADP) and platelet aggregating factor (PAF) induced platelet aggregation. Finally, NMDA increased cAMP levels in intact platelets, and such an effect did not occur in a Ca(2+)-free medium; yet, cAMP increase was not antagonized by the calmodulin inhibitor trifluoperazine (TFP). It was concluded that platelet membranes carry an NMDA receptor, functionally distinct from the neuronal one, which seems to play an anti-aggregating role

Role of ethanol-derived acetaldehyde in operant oral self-administration of ethanol in rats

Rationale: The role of ethanol-derived acetaldehyde has not been examined yet on performance in a model of operant oral self-administration. However, previous studies reported that an acetaldehyde-sequestering agent, d-penicillamine (DP) and an inhibitor of catalase-mediated acetaldehyde production, 3-amino-1,2,4-triazole (3-AT) reduce voluntary ethanol consumption. Objectives: The aim of our investigation was to evaluate the effects of DP and 3-AT on acquisition and maintenance of oral operant ethanol self-administration. Methods: Using operant chambers, rats learned to nose poke in order to receive ethanol solution (5-10 % v/v) under an FR1 schedule of reinforcement in which discrete light and tone cues were presented during ethanol delivery. Results: DP and 3-AT impair the acquisition of ethanol self-administration, whereas its maintenance is not affected neither by drug given alone for both 10 or 5 % ethanol nor by drugs association for 5 % ethanol. Moreover, when the concentration of ethanol was diminished from 10 to 5 %, rats increased the rate of self-administration behaviour. Conclusions: These findings suggest that brain acetaldehyde plays a critical role during acquisition of operant self-administration in ethanol-naïve rats. In contrast, during the maintenance phase, acetaldehyde could contribute to ethanol self-administration by a combined mechanism: On one hand, its lack (by DP or 3-AT) might result in further ethanol-seeking and taking and, on the other, inhibition of ethanol metabolism (by 3-AT) might release an action of the un-metabolised fraction of ethanol that does not overall result in compromising maintenance of ethanol self-administration