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 previo usly described monoclonal antibody (G-10), which inhibits L-alanine bi nding to a partial membrane fraction (P2) derived from catfish (lctalu rus punctatus) taste epithelium, was found in Western blots to recogni ze a single band, at apparent MW of 113,000 D. This MW differs from th e apparent MW for the presumed arginine receptor identified previously by PHA-E lectin affinity. In order to test whether PHA-E lectin actua lly reacts with the arginine-receptor, reconstituted membrane proteins partially purified by PHA-E affinity were used in artificial lipid bi layers. These reconstituted channels exhibited L-arginine-activated ac tivity similar to that found in taste cell membranes. Accordingly, we utilized the PHA-E lectin and G-10 antibody as probes to differentiall y localize the L-alanine and L-arginine binding sites on the apical su rface of catfish taste buds. Each probe labels numerous, small (0.5-1. 0 mu m) patches within the taste pore of each taste bud. This observat ion suggests that each bud is not tuned to a single taste substance, b ut 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, indic ating that this independent chemoreceptor system may utilize some rece ptor sites similar to those in taste buds. (C) 1996 Wiley-Liss, Inc.