Sugar-activated ion transport in canine lingual epithelium. Implications for sugar taste transduction.
There is good evidence indicating that ion-transport pathways in the apical regions of lingual epithelial cells, including taste bud cells, may play a role in salt taste reception. In this article, we present evidence that, in the case of the dog, there also exists a sugar-activated ion-transport pathway that is linked to sugar taste transduction. Evidence was drawn from two parallel lines of experiments: (a) ion-transport studies on the isolated canine lingual epithelium, and (b) recordings from the canine chorda tympani. The results in vitro showed that both mono- and disaccharides in the mucosal bath stimulate a dose-dependent increase in the short-circuit current over the concentration range coincident with mammalian sugar taste responses. Transepithelial current evoked by glucose, fructose, or sucrose in either 30 mM NaCl or in Krebs-Henseleit buffer (K-H) was partially blocked by amiloride. Among current carriers activated by saccharides, the current response was greater with Na than with K. Ion flux measurements in K-H during stimulation with 3-O-methylglucose showed that the sugar-evoked current was due to an increase in the Na influx. Ouabain or amiloride reduced the sugar-evoked Na influx without effect on sugar transport as measured with tritiated 3-O-methylglucose. Amiloride inhibited the canine chorda tympani response to 0.5 M NaCl by 70-80% and the response to 0.5 M KCl by approximately 40%. This agreed with the percent inhibition by amiloride of the short-circuit current supported in vitro by NaCl and KCl. Amiloride also partially inhibited the chorda tympani responses to sucrose and to fructose. The results indicate that in the dog: (a) the ion transporter subserving Na taste also subserves part of the response to K, and (b) a sugar-activated, Na-preferring ion-transport system is one mechanism mediating sugar taste transduction. Results in the literature indicate a similar sweet taste mechanism for humans.
Mierson
S
S
Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
DeSimone
S K
SK
Heck
G L
GL
DeSimone
J A
JA
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002241:Carbohydrates / Q000494:pharmacology*; D002814:Chorda Tympani Nerve / Q000502:physiology; D004285:Dogs / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000378:metabolism; D007477:Ions; D010695:Phlorhizin / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D013649:Taste / Q000502:physiology*; D014059:Tongue / Q000378:metabolism*
D002241:Carbohydrates; D007477:Ions; D012965:Sodium Chloride; D011189:Potassium Chloride; D000584:Amiloride; D010695:Phlorhizin