Dual effect of the acetylcholinesterase inhibitor caffeine on the muscle nicotinic acetylcholine receptor.

FABIANI, CAMILA; CORRADI, JEREMÍAS; ANA PAULA MURRAY; ANTOLLINI, SILVIA

Tucumán

Congreso; III Latin American Federation of Biophysical Societies (LAFeBS), IX IberoAmerican Congress of Biophysics, XLV Reunión Anual SAB 2016; 2016

Sociedad Argentina de Biofísica

Cholinergic deficit is regarded as an important factor responsible forAlzheimer?s disease symptoms. One of the molecular targets for thetreatment of this disease is acetylcholinesterase (AChE), an enzymethat hydrolyzes acetylcholine at the synaptic cleft. It has been shownthat some AChE inhibitors also act at nicotinic receptors (nAChR) potentiating their therapeutic effect. We found that metabolic extracts ofCamellia sinensis (red tea) exhibit a strong anticholinesterase activity.By chromatography and NMR spectroscopy we found that caffeine wasthe active compound exerting such effect. We next explored if caffeinehas a direct effect on the nAChR. Using the AChR conformational-sensitive probe crystal violet (CrV), an AChR open channel blocker, and AChR-rich membranes from Torpedo californica, we observed that increasing concentrations of caffeine (10-300 uM) decreased the KD of CrV in the resting state without changes in the KD in the desensitized state. In the presence of alpha-bungarotoxin, a specific AChR competitive antagonist, a dual effect was evident: low concentrations of caffeine did not produce any effect in the KD of CrV in the resting state, whereas higher concentrations produce a great increase of this value compatible with a competition with CrV for its site on the channel pore. To confirm this, we performed single channel recordings in Bosc cells expressing the adult muscle nAChR in the presence of 30 uM ACh and increasing concentrations of caffeine (150-20000 uM). We found that the mean open duration decreases, and the relative area of the briefer closed component and the cluster duration increase as a function of caffeine concentration. All these observations are compatible with an open channel blocker. Thus, our results suggest a dual effect of caffeine onthe muscle AChR: at low concentrations, in the absence of agonist, induces an AChR conformational change, whereas at high concentrations caffeine acts as an AChR open channel blocker.