Differential localization of putative amino acid receptors in taste buds of the channel catfish, Ictalurus punctatus.
The taste system of catfish, having distinct taste receptor sites for L-alanine and L-arginine, is highly sensitive to amino acids. A previously described monoclonal antibody (G-10), which inhibits L-alanine binding to a partial membrane fraction (P2) derived from catfish (Ictalurus punctatus) taste epithelium, was found in Western blots to recognize a single band, at apparent MW of 113,000 D. This MW differs from the apparent MW for the presumed arginine receptor identified previously by PHA-E lectin affinity. In order to test whether PHA-E lectin actually reacts with the arginine-receptor, reconstituted membrane proteins partially purified by PHA-E affinity were used in artificial lipid bilayers. These reconstituted channels exhibited L-arginine-activated activity similar to that found in taste cell membranes. Accordingly, we utilized the PHA-E lectin and G-10 antibody as probes to differentially localize the L-alanine and L-arginine binding sites on the apical surface of catfish taste buds. Each probe labels numerous, small (0.5-1.0 micron) patches within the taste pore of each taste bud. This observation suggests that each bud is not tuned to a single taste substance, but contains putative receptor sites for both L-arginine and L-alanine. Further, analysis of double-labeled tissue reveals that the PHA-E and G-10 sites tend to be separate within each taste pore. These findings imply that in catfish, individual taste cells preferentially express receptors to either L-arginine or L-alanine. In addition, PHA-E binds to the apices of solitary chemoreceptor cells in the epithelium, indicating that this independent chemoreceptor system may utilize some receptor sites similar to those in taste buds.
Finger
T E
TE
Department of Cellular and Structural Biology, Rocky Mountain Taste and Small Center, University Colorado Health Sciences Center, Denver, Colorado 80262, USA. Tom.Finger@UCHSC.EDU
Bryant
B P
BP
Kalinoski
D L
DL
Teeter
J H
JH
Böttger
B
B
Grosvenor
W
W
Cagan
R H
RH
Brand
J G
JG
D000409:Alanine / Q000378:metabolism*; D000818:Animals; D000911:Antibodies, Monoclonal; D001120:Arginine / Q000378:metabolism*; D006652:Histological Techniques; D007059:Ictaluridae / Q000378:metabolism*; D015640:Ion Channel Gating; D015335:Molecular Probes; D010835:Phytohemagglutinins; D017459:Receptors, Amino Acid / Q000378:metabolism*; D013650:Taste Buds / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D015335:Molecular Probes; D010835:Phytohemagglutinins; D017459:Receptors, Amino Acid; C098464:alanine receptor; C067494:erythroagglutinating phytohemagglutinin; D001120:Arginine; D000409:Alanine