Review of Functional Studies of Beverage Components Acting on the Recombinant GABAA Neuroreceptor, and Na+/Glucose Cotransporter-Response Using the Xenopus Oocyte Expression System and Electrophysiological Measurements

Abstract

Beverages such as teas, coffee, cacao, and liquors are produced in large quantities and consumed all over the world. Natural components from beverages affect neurotransmitter receptors, especially the GABAA receptors, which are involved in defining mental state and therefore have role in stress management in modern society. These components of beverages modulating the responses of GABAA receptors or other neurotransmitter receptors that affect mental state linked to stress and mood can easily be detected by expressing the receptors in Xenopus oocytes and making voltage-clamp electrophysiological measurements. This approach could be extended to detect food-components, which are functionally active on various transporters such as Na+/glucose cotransporters operating in the small intestines to transport glucose into blood, which are inhibited by (+)-catechin and its derivatives in teas. Using this technique, it has become apparent that beverages for stress and mood management must have long-chain normal alcohols but short-chain esters, and phenol derivatives having low numbers of OH- or phenol groups in addition to fragrant compounds such as geraniol, linalool, cis-jasmone, methyl jasmonate, 1-octen-3-ol, myrcenol, terpinen-4-ol and ethyl phenyl propanoate. The technique could also be used easily to assess the toxicity of food-components to cells, as was reported for saponin and tannic acid which produce large electrical responses in the oocyte. Further, (+)-catechin and its derivatives, and aqueous extracts of coffee, green tea, oolong tea and black tea, dose-dependently produce nonspecific currents, suggesting that high concentrations of these beverages may be detrimental to health.