Cholinergic currents in Xenopus oocytes transplanted with human brain membranes

Corrientes colinérgicas de cerebro humano fueron registradas en oocitos de Xenopus laevis trasplantados con membranas de cerebro humano procedentes de dos zonas diferentes, la corteza frontal y el hipocampo. Las corrientes registradas fueron activadas por el receptor nicotínico o por el receptor nicotínico o muscarínico de la acetilcolina. Se probaron los efectos de diferentes agonistas nicotínicos como acetilcolina, nicotina y yoduro de 1,1-dimetil-4-fenil-piperazinio (DMPP), y antagonistas del receptor nicotínico como a-bungarotoxina y d-tubocurarina en los oocitos transplantados. Detectamos cuatro clases de cinéticas de corrientes nicotínicas. Las diferencias en la amplitud y en la carga eléctrica total de las corrientes provocadas por varios agonistas en el rango de potencial mantenido no fueron significativas, excepto en el caso del DMPP a un potencial mantenido de -90 mV. Nuestros resultados indican que las formas alfa4beta2, alfa3beta4 y alfa7 son los principales receptores nicotínicos en el cerebro humano

Cholinergic human brain currents were recorded in Xenopus laevis oocytes transplanted with human cerebral membranes from two different zones, the frontal cortex and the hippocampus. The recorded currents were supported by the nicotinic or the muscarinic acetylcholine receptor. We tested the effects of a number of several nicotinic agonists acetylcholine, nicotine and 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), and the nicotinic receptor antagonists a-bungarotoxin and d-tubocurarine on the transplanted oocytes. We detected four kinds of nicotinic current kinetics. The differences in the amplitude and in the total electric charge of the currents elicited by various agonists at a range of holding potentials were not significant, except in the case of DMPP at a holding potential of -90 mV. Our results indicate that alpha4beta2, alpha3beta4 and alpha7 are the main nicotinic receptors in human brain

Effect of galantamine on the human alpha7 neuronal nicotinic acetylcholine receptor, the Torpedo nicotinic acetylcholine receptor and spontaneous cholinergic synaptic activity.

1. Various types of anticholinesterasic agents have been used to improve the daily activities of Alzheimer's disease patients. It was recently demonstrated that Galantamine, described as a molecule with anticholinesterasic properties, is also an allosteric enhancer of human alpha4beta2 neuronal nicotinic receptor activity. We explored its effect on the human alpha7 neuronal nicotinic acetylcholine receptor (nAChR) expressed in Xenopus oocytes. 2. Galantamine, at a concentration of 0.1 microM, increased the amplitude of acetylcholine (ACh)-induced ion currents in the human alpha7 nAChR expressed in Xenopus oocytes, but caused inhibition at higher concentrations. The maximum effect of galantamine, an increase of 22% in the amplitude of ACh-induced currents, was observed at a concentration of 250 microM Ach. 3. The same enhancing effect was obtained in oocytes transplanted with Torpedo nicotinic acetylcholine receptor (AChR) isolated from the electric organ, but in this case the optimal concentration of galantamine was 1 microM. In this case, the maximum effect of galantamine, an increase of 35% in the amplitude of ACh-induced currents, occurred at a concentration of 50 microM ACh. 4. Galantamine affects not only the activity of post-synaptic receptors but also the activity of nerve terminals. At a concentration of 1 microM, quantal spontaneous events, recorded in a cholinergic synapse, increased their amplitude, an effect which was independent of the anticholinesterasic activity associated with this compound. The anticholinesterasic effect was recorded in preparations treated with a galantamine concentration of 10 microM. 5. In conclusion, our results show that galantamine enhances human alpha7 neuronal nicotinic ACh receptor activity. It also enhances muscular AChRs and the size of spontaneous cholinergic synaptic events. However, only a very narrow range of galantamine concentrations can be used for enhancing effects.

Gadolinium inhibition of ecto-nucleoside triphosphate diphosphohydrolase activity in Torpedo electric organ.

Ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) are widely expressed enzymes implicated in the modulation of nucleotide cell signaling. They dephosphorylate either ATP or ADP in the presence of divalent cations, and efforts have been made to identify efficient inhibitors. E-NTPDase activity has been described in Torpedo electric organ electrocytes. We show here that gadolinium, an established blocker of stretch-activated channels, efficiently inhibits E-NTPDase activity of Torpedo electric organ (Ki = 3 microM for ATPase) as well as apyrase from potato tuber, frequently used in inhibition experiments. To our knowledge, gadolinium is the most potent inhibitor described to date for both membrane-bound and soluble E-NTPDases.