Physiological evidence for the discrimination of L-arginine from structural analogues by the zebrafish olfactory system.
Although it is generally assumed that fish are capable of discriminating amino acid odorants on the basis of differences in side-chain structure, less is known about their ability to discriminate amino acids with modifications to alpha-carboxyl and alpha-amino groups. In this study, the ability of the zebrafish olfactory system to detect and presumably discriminate analogues of the basic amino acid Arg was assessed, by using cross-adaptation and activity-dependent labeling techniques. Electrophysiological recordings established that esterification (L-arginine methyl ester; AME) or deletion (agmatine or amino-4-guanidobutane; AGB) of the alpha-carboxyl group yielded odorants more potent than Arg, whereas deletion of the alpha-amino group (L-argininic acid; AA) yielded a less potent analogue. In cross-adaptation experiments, no test-competitor odorant combination yielded complete cross-adaptation, suggesting the detection of these Arg analogues by multiple odorant receptors (ORs) with partially nonoverlapping specificities. Activity-dependent immunocytochemical labeling of olfactory receptor neurons supported this conclusion. AGB, an ion-channel-permeant probe (and odorant), labeled 4.9 +/- 0.4% (n = 24) of sensory epithelium, whereas the addition of Arg, 1-ethylguanidine sulfate, L-alpha-amino-beta-guanidinopropionate, or AME to AGB resulted in a significant elevation of labeling (8-14%). This study provides evidence that the olfactory system has the potential to discriminate among amino acid odorants with modified alpha-carboxyl and alpha-amino groups.
Lipschitz
D L
DL
Department of Physiology, University of Utah School of Medicine, Salt Lake City, Utah 84108-1270, USA.
Michel
W C
WC
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004192:Discrimination, Psychological / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D008297:Male; D009812:Odorants; D018034:Olfactory Receptor Neurons / Q000502:physiology*; D012903:Smell / Q000502:physiology*; D013329:Structure-Activity Relationship; D015027:Zebrafish
D001120:Arginine