Receptor Potentials In Taste Cells Research Articles

Non-synaptic transformation of gustatory receptor potential by stimulation of the parasympathetic fiber of the frog glossopharyngeal nerve.

When the glossopharyngeal nerve (GP) in the frog was strongly stimulated electrically, slow potentials were elicited from the tongue surface and taste cells in the fungiform papillae. Injection of atropine completely blocked these slow potentials. The present and previous data indicate that the slow potentials induced in the tongue surface and taste cells are due to a liquid junction potential between saliva secreted from the lingual glands due to parasympathetic fiber activity and an adapting solution on the tongue surface. Intracellularly recorded depolarizing receptor potentials in taste cells induced by 0.5 M NaCl and 3 mM acetic acid were enhanced by depolarizing slow potentials induced by GP nerve stimulation, but were depressed by the hyperpolarizing slow potentials. On average, the receptor potential of taste cells for 0.5 M NaCl was increased by 25% by the GP nerve-induced slow potential, but the receptor potential of taste cells for 3 mM acetic acid was decreased by 1% by the slow potential. These transformations of receptor potentials in frog taste cells were not due to a synaptic event initiated between taste cells and the efferent nerve fiber, but due to a non-synaptic event, a lingual junction potential generated in the dorsal lingual epithelium by GP nerve stimulation.

Contribution of proton transporter to acid-induced receptor potential in frog taste cells

1. 1. The generative mechanism of the acid-induced receptor potential in frog taste cells was re-examined with micro-electrodes. 2. 2. The amplitude of receptor potentials in a taste cell induced by 1 mM acetic acid increased as the concentration of Ca 2+, Sr 2+ and B 2+ on the tongue surface was increased. 3. 3. The amplitude of the acid-induced receptor potential was inhibited by about 40% by a proton pump blocker DCCD ( N,N′-dicyclohexylcarbodiimide) added to superficial normal saline. 4. 4. It is concluded that most of the acid-induced response in a frog taste cell was generated by current carried through proton-gated C 2+ channel of the apical receptive membrane. The remaining part of the acid response was generated by current carried through a DCCD-sensitive proton transporter of the receptive membrane.

Mediation of Responses to Calcium in Taste Cells by Modulation of a Potassium Conductance

Calcium salts are strong taste stimuli in vertebrate animals. However, the chemosensory transduction mechanisms for calcium are not known. In taste buds of Necturus maculosus (mud puppy), calcium evokes depolarizing receptor potentials by acting extracellularly on the apical ends of taste cells to block a resting potassium conductance. Therefore, divalent cations elicit receptor potentials in taste cells by modulating a potassium conductance rather than by permeating the cell membrane, the mechanism utilized by monovalent cations such as sodium and potassium ions.

Chemotransduction in necturus taste buds, a model for taste processing

The taste bud in Necturus serves as a good model for taste mechanisms in vertebrates. The large size of taste cells and relative accessibility of the tissue for detailed electrophysiological and ultrastructural studies makes this species well-suited for studying taste transduction. Important features of taste transduction that have been learned from investigations in Necturus are that voltage-gated potassium channels are preferentially distributed on the apical membrane of taste cells; voltage-gated potassium channels allow K ions to enter the cell when taste buds are stimulated with K salts; some chemical stimuli act by closing K channels, thereby eliciting depolarizing receptor potentials in taste cells. Many of these findings have been confirmed and extended in other animals, including mammals. Furthermore, recent evidence from experiments in Necturus suggests that there is a considerable degree of synaptic coupling among taste cells. This synaptic coupling could form the basis for signal processing and integration in the peripheral sensory organs of taste, the taste buds.

Response characteristics of rat taste cells to potassium benzoate

1. 1. The rat taste cells responded to K-benzoate solutions higher than the threshold concentrations (0.03–0.3 M) with a depolarizing receptor potential, but they responded to K-benzoate lower than the thresholds with a hyperpolarizing receptor potential. 2. 2. In either depolarizing or hyperpolarizing receptor potentials the rise time decreased with increasing amplitude, but the fall time increased with increasing amplitude. 3. 3. During generation of either depolarizing or hyperpolarizing receptor potentials the input resistance of taste cells decreased with increasing amplitude. 4. 4. Application of the mixtures of various concentrations of NaCl and 0.05 M K-benzoate resulted in a reduction of receptor potential amplitude, as compared with that evoked by application of NaCl alone. 5. 5. It is concluded that a depression of gustatory neural impulse frequency by low concentrations of K-benzoate is mainly due to the hyperpolarizing receptor potential of taste cells elicited by the K-benzoate solutions.

Topographical difference in taste organ density and its sensitivity of frog tongue

1. 1. Distribution density of the taste disks of the fungiform papillae in the frog tongue was larger at the proximal portion than at the apical and middle portions. The number of myelinated afferent nerve fibres and taste cells per cm 2 area of the tongue increased in the order of proximal > middle > apical portion. 2. 2. The amplitudes of gustatory neural responses for 0.5 M NaCl, 0.5 M KCl, 0.5 M NH 4Cl, 0.05 M CaCl 2, 1 mM acetic acid and 1 mM quinine-HCl (Q-HCl) were significantly larger with lingual stimulation of the proximal region than with the stimulation of the apical region. With these stimuli the mean ratio of the apical response to the proximal response was 1.00:1.54. On the other hand, this ratio with deionized water was 1.00:5.00. 3. 3. The mean magnitudes of receptor potentials in taste cells for 1 mM acetic acid and 10 mM Q-HC1 were the same among the apical, middle and proximal portions of the tongue. The mean magnitudes of receptor potentials for 0.5 M NaCl were significantly larger at the apical portion than at the other portions, whereas those for deionized water tended to be the largest at the proximal portion. 4. 4. It is concluded that the larger magnitude of the gustatory neural responses at the proximal portion of the tongue is due to morphological and physiological properties of the taste organ.

An initial phasic depolorization exists in the receptor potential of taste cells

When frog taste cells were stimulated by varying salts after adaptation to water, quinine or acetic acid, a phasic depolarization appeared initially in the receptor potential of taste cells. The initial transient depolarization may be related to the enhancement of an initial phasic response in the taste nerve.

Does an initial phasic response exist in the receptor potential of taste cells?

The depolarizing receptor potentials to 0.5 M NaCl recorded from frog taste cells did not exhibit any phasic response, even when the rectangular waveform of stimulus onset was employed. The quickest depolarizations recorded reached the peak in 50 msec. On the other hand, the gustatory neural response showed initial overshoot of the impulse discharge even when 0.5 M NaCl was delivered at the slower rate of 0.06 ml/sec. It is concluded that the initial neural response may be associated with the rate of rise of the receptor potential before its plateau level is reached.