Gq alpha subunit mediates receptor site-specific adaptation in the sugar taste receptor cell of the blowfly, Phormia regina.
The gustatory system is essential for almost all animals. The recent identification of G protein-coupled receptor proteins (GPCRs) has progressed molecular biological studies of gustatory systems, although the signal transduction mechanisms have not yet been fully elucidated. In vision and olfactory receptor cells, Gq class G protein is known to be a major signal transducer. By functional blocking of intrinsic Gq with an anti-Gq/11alpha antibody, we investigated the roles of Gq in the sugar receptor cell of the blowfly, Phormia regina. Before and after introduction of the anti-Gq/11alpha antibody into the cell through the DOC-permeabilized cell membrane, we recorded the responses of the receptor cell to sucrose and d-fructose, which stimulate different receptor sites, respectively. The initial impulse frequency in response to either sucrose or D-fructose was not changed by antibody introduction, whereas the adaptation rate in sucrose stimulation, but not fructose stimulation, became slower after antibody introduction. These results indicate that: (1) Gq is a regulator of adaptation in the sugar receptor cell of Phormia, rather than a transducer, and (2) different adaptation mechanisms are promoted by stimulations with sucrose and D-fructose.