A quinine-activated cationic conductance in vertebrate taste receptor cells.
The chincona alkaloid quinine is known to be a bitter tasting substance for various vertebrates. We examined the effects of quinine on isolated taste receptor cells from the bullfrog (Rana catesbeiana). Membrane currents were recorded by whole-cell recording, while quinine hydrochloride was applied extracellularly from a puffer pipette. At the resting potential (-77 +/- 9 mV, mean +/- SD, n = 49 cells), taste cells generated inward currents in response to quinine stimulation (> 1 mM), indicating a depolarizing response in the taste cells. Two types of current responses were observed; a newly found quinine-activated cationic conductance and a previously reported blocking effect of quinine on K+ conductances. The cationic current was isolated from the K+ current by using a Cs(+)-containing patch pipette. The relative permeabilities (Pion) of the quinine-activated cationic conductance were: PNa/PK/PCs = 1:0.5:0.42. The quinine dose-response relation was described by the Hill equation with the K1/2 of 3.6 mM and Hill coefficient of 5.3. When extracellular [Ca2+] (1.8 mM) was reduced to nominally free, the conductance was enhanced by about sixfold. This property is consistent with observations on quinine responses recorded from the gustatory nerve, in vivo. The quinine-induced cationic current was decreased with an application of 8-bromo-cAMP. We conclude that the bitter substance quinine activates a cation channel in taste receptor cells and this channel plays an important role in bitter taste transduction.
Tsunenari
T
T
Research Institute for Food Science, Kyoto University, Japan.
Hayashi
Y
Y
Orita
M
M
Kurahashi
T
T
Kaneko
A
A
Mori
T
T
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002412:Cations / Q000378:metabolism*; D002586:Cesium / Q000378:metabolism; D000242:Cyclic AMP / Q000031:analogs & derivatives; D004553:Electric Conductivity; D005110:Extracellular Space / Q000378:metabolism; D007477:Ions; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000037:antagonists & inhibitors / Q000502:physiology; D011803:Quinine / Q000494:pharmacology*; D011892:Rana catesbeiana; D011984:Sensory Receptor Cells / Q000187:drug effects* / Q000502:physiology*; D013649:Taste / Q000502:physiology*
D002412:Cations; D007477:Ions; D002586:Cesium; D015124:8-Bromo Cyclic Adenosine Monophosphate; D011803:Quinine; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium