Odorants selectively activate distinct G protein subtypes in olfactory cilia.
Chemoelectrical signal transduction in olfactory neurons appears to involve intracellular reaction cascades mediated by heterotrimeric GTP-binding proteins. In this study attempts were made to identify the G protein subtype(s) in olfactory cilia that are activated by the primary (odorant) signal. Antibodies directed against the alpha subunits of distinct G protein subtypes interfered specifically with second messenger reponses elicited by defined subsets of odorants; odor-induced cAMP-formation was attenuated by Galphas antibodies, whereas Galphao antibodies blocked odor-induced inositol 1,4, 5-trisphosphate (IP3) formation. Activation-dependent photolabeling of Galpha subunits with [alpha-32P]GTP azidoanilide followed by immunoprecipitation using subtype-specific antibodies enabled identification of particular individual G protein subtypes that were activated upon stimulation of isolated olfactory cilia by chemically distinct odorants. For example odorants that elicited a cAMP response resulted in labeling of a Galphas-like protein, whereas odorants that elicited an IP3 response led to the labeling of a Galphao-like protein. Since odorant-induced IP3 formation was also blocked by Gbeta antibodies, activation of olfactory phospholipase C might be mediated by betagamma subunits of a Go-like G protein. These results indicate that different subsets of odorants selectively trigger distinct reaction cascades and provide evidence for dual transduction pathways in olfactory signaling.
Schandar
M
M
Universität Stuttgart-Hohenheim, Institut für Physiologie, 70593 Stuttgart, Germany.
Laugwitz
K L
KL
Boekhoff
I
I
Kroner
C
C
Gudermann
T
T
Schultz
G
G
Breer
H
H
D000085:Acetates / Q000494:pharmacology; D000447:Aldehydes / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001547:Benzaldehydes / Q000494:pharmacology; D002923:Cilia / Q000187:drug effects* / Q000378:metabolism; D000242:Cyclic AMP / Q000096:biosynthesis; D053138:Cyclohexenes; D003517:Cyclopentanes / Q000494:pharmacology; D005054:Eugenol / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009570:Nitriles / Q000494:pharmacology; D009812:Odorants; D009831:Olfactory Mucosa / Q000187:drug effects* / Q000378:metabolism; D054883:Oxylipins; D019920:Photoaffinity Labels; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects
D000085:Acetates; D000447:Aldehydes; D001547:Benzaldehydes; D053138:Cyclohexenes; D003517:Cyclopentanes; D009570:Nitriles; D054883:Oxylipins; D019920:Photoaffinity Labels; D005054:Eugenol; C054764:citralva; D015544:Inositol 1,4,5-Trisphosphate; C072239:methyl jasmonate; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; C092244:hydroxyisohexyl 3-cyclohexene carboxaldehyde; C038018:lilial; C045941:ethyl vanillin