A Basolateral Amiloride-Sensitive Na+-Transport Pathway in Rat Tongue
Sheella Mierson, Michelle M. Olson, and Amy E. Tietz.
Department of Biology, University of Delaware, Newark, DE 19716.
APStracts 3:0050N, 1996.
SUMMARY AND CONCLUSIONS
1. Experiments were conducted to test for the presence of basolateral Na +
channels in the rat lingual epithelium. Ye et al. (1993) and Rehnberg et al.
(1993) proposed a model in which some lingual taste cells have Na + channels
in the basolateral membrane. That model is designed to account for the portion
of the neural taste response and the portion of the transepithelial short-
circuit current (I sc ) in vitro that are insensitive to mucosal amiloride;
some Na + would diffuse across the tight junction, into the cell via this
lateral pathway, and be transported out of the cell by Na + pumps in the basal
membrane. The model could also account for the differential effect of mucosal
amiloride on Na + salts of various anions, in which the neural taste responses
to Na + salts with anions larger than Cl - are more sensitive to mucosal
amiloride than is the taste response to NaCl. 2. Voltage-clamp data were
obtained from an in vitro preparation of the dorsal rat tongue epithelium in
which the connective tissue was removed by enzyme digestion. I sc in a
modified Ussing chamber was reduced by amiloride in the submucosal solution.
3. The pattern of sensitivity to submucosal amiloride differed in several
respects from the pattern for mucosal amiloride. The K i was 52 [mu]M
amiloride concentration, higher than for the apical amiloride-sensitive Na
channel. The selectivity for Na + over K + was much less than for the response
to mucosal amiloride; with 0.5 M NaCl or KCl on the mucosal side, the ratio of
inhibition for the NaCl response to inhibition for the KCl response varied
between 1 and 3. 4. As the concentration of NaCl in the mucosal solution was
varied, submucosal amiloride caused little inhibition of I sc for mucosal NaCl
below isosmotic concentration, with the percent inhibition increasing as
mucosal salt concentration increased. With 0.5 M sodium gluconate in the
mucosal solution, there was very little inhibition due to submucosal
amiloride. 5. The results support the presence of amiloride-sensitive Na +
channels in the basolateral membranes of the dorsal tongue epithelium in rat,
and are consistent with the proposed model in which these channels are present
in taste cells.
Received 19 June 1995; accepted in final form 7 February 1996.
APS Manuscript Number J394-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96