Role of the G-protein subunit alpha-gustducin in taste cell responses to bitter stimuli.
Many bitter stimuli are believed to bind to specific G-protein-coupled membrane receptors on taste cells. Despite the compelling evidence for its pivotal role in bitter taste sensation, a direct involvement of the G-protein subunit alpha-gustducin in bitter taste transduction in taste cells has not been demonstrated in situ at the cellular level. We recorded activation of taste cells by bitter stimuli using Ca2+ imaging in lingual slices and examined alpha-gustducin immunoreactivity in the same cells. In mice vallate papillae, many, but not all, bitter-responsive cells expressed alpha-gustducin. In agreement with this correlation, the incidence of cells responding to bitter stimuli was reduced by 70% in mutant mice lacking alpha-gustducin. Nevertheless, some taste cells lacking alpha-gustducin responded to bitter stimuli, suggesting that other G-protein alpha subunits are involved. We found that the G-protein alpha subunit Galpha(i2) is present in most bitter-responsive cells and thus may also play a role in bitter taste transduction. The reduced behavioral sensitivity to bitter stimuli in alpha-gustducin knock-out mice thus appears to be the consequence of a reduced number of bitter-activated taste cells, as well as reduced sensitivity.
Department of Physiology and Biophysics and Program in Neuroscience, University of Miami School of Medicine, Miami, Florida 33136, USA. acaicedo@chroma.med.miami.edu
Alejandro
A
Caicedo
Elizabeth
E
Pereira
Robert F
RF
Margolskee
Stephen D
SD
Roper
D000818:Animals; D002118:Calcium / Q000378:metabolism; D019343:Citric Acid / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D021122:Protein Subunits / Q000378:metabolism / Q000502:physiology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology; D013268:Stimulation, Chemical; D013649:Taste / Q000187:drug effects / Q000502:physiology*; D013650:Taste Buds / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015293:Transducin / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
D002118:Calcium; D019343:Citric Acid; D003513:Cycloheximide; D021122:Protein Subunits; D000644:Quaternary Ammonium Compounds; D011803:Quinine; D015293:Transducin; C075192:gustducin; C043414:denatonium