Journal of Neuroscience, Vol 6, 2611-2615, Copyright © 1986 by Society for Neuroscience
Antagonism of the gerbil's sucrose taste response by p-nitrophenyl alpha-D-glucopyranoside and chloramphenicol
V Vlahopoulos and W Jakinovich Jr
We have discovered that the gerbil's chorda tympani nerve response to
sucrose is suppressed by p-nitrophenyl alpha-D-glucopyranoside (PNP- Glu)
and chloramphenicol (CAP). Mixture experiments of PNP-Glu and CAP with
sodium chloride, potassium chloride, hydrochloric acid, and sucrose gave
rise to the following observations: Neither PNP-Glu nor CAP alone
stimulates the gerbil's taste nerve; while the sucrose response is
suppressed by these inhibitors, taste responses produced by sodium
chloride, potassium chloride, and hydrochloric acid are unaffected by the
presence of PNP-Glu or CAP; the antagonisms of PNP- Glu and CAP were
surmounted by a high concentration of sucrose; CAP is a more potent
antagonist (IC50 = 0.0013 M) than PNP-Glu (IC50 = 0.022 M), and both are
more potent than methyl 4,6-dichloro-4,6-dideoxy-alpha- D-galactopyranoside
(IC50 = 0.048 M); and sucrose antagonism occurs only when PNP-Glu and CAP
are mixed with sucrose. It is short-lived and ceases when the mixtures are
rinsed from the gerbil's tongue. Structure- activity studies provided the
following information: The alpha anomer of PNP-Glu is a more potent
inhibitor than its beta anomer; among the PNP-Glu derivatives tested
(p-aminophenyl, p-nitrophenyl, and phenyl) only p-nitrophenyl inhibited;
among the nitrophenyl galactosides, the para derivative was more potent
than the ortho or meta; and p- nitrophenyl alpha-D-mannopyranoside and
p-nitrophenyl alpha-D- galactoside are slightly more potent than PNP-Glu.
On the basis of concentration experiments, we believe that the inhibitory
mechanisms of PNP-Glu and CAP are different, which suggests the existence
of at least 2 sucrose receptor sites.