Arterial perfusion of frog tongue for intracellular recording of taste cell receptor potential

Ionic basis of receptor potential of frog taste cells induced by acid stimuli

1. The ionic mechanism underlying the receptor potential in frog taste cells induced by acid stimuli was studied with single microelectrodes by replacing superficial and interstitial fluids of the tongue with modified saline solutions. 2. The removal of Na+, Ca2+ and Cl- from the normal interstitial fluid did not affect the receptor potential induced by acid stimuli. Interstitial 100 mM-K+ saline did not affect the acid response. 3. The receptor potential was reduced greatly when Ca2+ was removed from the superficial saline, but was increased when the Ca2+ concentration was elevated. The removal of superficial Cl- did not affect the receptor potential. The receptor potential elicited by superficial Ca2+-free saline was partly due to Na+. Li+, K+, NH4+ or choline + substituted for Na+ in producing the receptor potential. The amiloride-sensitive Na+ channel on the receptor membrane did not contribute to the receptor potential. With pure water adaptation of the tongue surface, the mean magnitude of the acid response was 35% of the control. 4. The receptor potential was unaffected by superficial tetrodotoxin (TTX) but was blocked by superficial Ca2+ antagonists such as Co2+ and Cd2+. Sr2+ substituted for Ca2+ in generating the receptor potential. 5. The receptor potentials observed under various concentrations of superficial Ca2+ became smaller when Na+ was present in the superficial fluid, indicating a competition between Ca2+ and Na+. 6. It is concluded that a large portion of the receptor potential induced by acid stimuli is produced by cations passing through a tastant-gated Ca2+ channel on the taste receptor membrane. Both divalent (Ca2+, Sr2+) and monovalent (Na+, Li+, K+, NH4+, choline+) cations can pass through the Ca2+ channel. The other mechanism responsible for the remaining part of the receptor potential is discussed.

Membrane properties of isolated mudpuppy taste cells

The voltage-dependent currents of isolated Necturus lingual cells were studied using the whole-cell configuration of the patch-clamp technique. Nongustatory surface epithelial cells had only passive membrane properties. Small, spherical cells resembling basal cells responded to depolarizing voltage steps with predominantly outward K+ currents. Taste receptor cells generated both outward and inward currents in response to depolarizing voltage steps. Outward K+ currents activated at approximately 0 mV and increased almost linearly with increasing depolarization. The K+ current did not inactivate and was partially Ca++ dependent. One inward current activated at -40 mV, reached a peak at -20 mV, and rapidly inactivated. This transient inward current was blocked by tetrodotoxin (TTX), which indicates that it is an Na+ current. The other inward current activated at 0 mV, peaked at 30 mV, and slowly inactivated. This more sustained inward current had the kinetic and pharmacological properties of a slow Ca++ current. In addition, most taste cells had inwardly rectifying K+ currents. Sour taste stimuli (weak acids) decreased outward K+ currents and slightly reduced inward currents; bitter taste stimuli (quinine) reduced inward currents to a greater extent than outward currents. It is concluded that sour and bitter taste stimuli produce depolarizing receptor potentials, at least in part, by reducing the voltage-dependent K+ conductance.