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PubMed1993

Freeze-fracture characterization of cell types at the surface of the taste organ of the frog, Rana esculenta.

The ultrastructure and distribution of intramembrane particles in the chemoreceptor surface of the frog taste organ have been studied by means of freeze-fracture. Sustentacular, wing, mucous cells and two different types of putative taste cells were found to reach the free surface of this chemoreceptor. Each of these cell types was characterized by a different pattern and density of intramembrane particles in the free surface. Wing cells displayed a relatively low number of large intramembrane particles (11.1 +/- 1.4 nm in diameter). Particles of similar size were also present in a much higher concentration in the membrane of cylinder-ending putative taste cells. In microvilli-ending putative taste cells, mucous cells, and sustentacular cells, small intramembrane particles were observed (6.8 +/- 0.78, 6.9 +/- 1.3, 7.2 +/- 0.7 nm in diameter, respectively). The density of these particles was higher in the sustentacular cells than in the other two cell types. These data provide evidence that there are two morphologically distinct types of putative taste cells in the frog taste organ, demonstrating that they are characterized by different pattern of intramembrane particles in their free surface. Furthermore, the present results support previous findings indicating that wing and sustentacular elements represent two different cell types.

Animals↗
PubMedDate not supplied

Impulse activity of medulla oblongata in rats in response to stimulation of taste receptors and visceral chemoreceptors.

We have recorded extracellularly the impulse activity of the rat medulla oblongata during stimulation of taste receptors of the tongue and visceral chemoreceptors with solutions of hydrochloric acid and sodium chloride. We have detected in the caudal region of the nucleus of the solitary tract, neurons that react to the chemical stimulation of either one or both the receptive zones mentioned. The response reactions of the isolated groups of units (taste, viscerochemical, and convergent neurons) are tonic and are characterized by a high level of impulse activity. We have established that the neurons of each of the groups isolated are capable of discriminating between salt and acid solutions. Using the example of sodium chloride solutions we have shown that an increase in the number of viscerochemical neurons which inhibit their own background activity on increase in the concentration of any substance in the intestine is an important index of the satiation of an animal and can serve as a starting link in the mechanism of food rejection.

Animals↗
PubMed1978

Correlation of chemical structure and taste in the cyclamate series and the steric nature of the chemoreceptor site.

The requirements of compounds in the cyclamate series for sweet taste stimulation are: synclinal conformation between NH and SO in the aminosulphonate group, length less than 0.7 nm of the group on the nitrogen, and hydrophobic character of the latter group. A hypothetical receptor site for these compounds should have a spatial barrier at a distance of about 0.7 nm from the nitrogen interaction point with the receptor site, and a hydrophobic interaction area between the nitrogen interaction point and the barrier.

Chemical Phenomena↗
PubMed1985

Influence of atropine on taste-stimulated parotid secretion.

Elemental taste qualities as "sour" and "sweet" showed different stimulatory effects on the parotid secretion when given in concentrations with comparable gustatory intensity. Sweet (fructose 10%) exerted an adrenergic-like activity, sour (citric acid 1%) a more parasympathetic-like influence on parotid secretion. The vagal pathway of the gustatory stimuli was further investigated by the simultaneous infusion of atropine sulfate (17 micrograms/kg per 30 min). Atropine reduced the flow rate during sour and sweet stimulation in the range of 500% and 300%. In 60% of the test persons parotid flow rate could not be totally depressed in any of three 10-min sampling fractions by atropine when a sour stimulus was applied; in these subjects protein and amylase concentration increased significantly. Following fructose stimulation the flow rate was totally depressed in all subjects by atropine in the 20- and 30-min sampling fractions. In the first 10-min fraction protein and amylase concentration were not influenced by atropine. The cholinergic pathway seems to be responsible primarily for the flow rate and has further different modulating influence on the stimulatory effect of the individual taste qualities.

Adult↗
PubMed1987

Patch-clamp study of isolated taste receptor cells of the frog.

Taste discs were dissected from the tongue of R. ridibunda and their cells dissociated by a collagenase/low Ca/mechanical agitation protocol. The resulting cell suspension contained globular epithelial cells and, in smaller number, taste receptor cells. These were identified by staining properties and by their preserved apical process, the tip of which often remained attached to an epithelial (associated) cell. When the patch pipette contained 110 mM KCl and the cells were superfused with NaCl Ringer's during whole-cell recording, the mean zero-current potential of 22 taste receptor cells was -65.2 mV and the slope resistance 150 to 750 M omega. Pulse-depolarization from a holding voltage of -80 mV activated a transient TTX-blockable inward Na current. Activation became noticeable at -25 mV and was half-maximal at -8 mV. Steady-state inactivation was half-maximal at -67 mV and complete at -50 mV. Peak Na current averaged -0.5 nA/cell. The Ca-ionophore A23187 shifted the activation and inactivation curve to more negative voltages. Similar shifts occurred when the pipette Ca was raised. External Ni (5 mM) shifted the activation curve towards positive voltages by 10 mV. Pulse depolarization also activated outward K currents. Activation was slower than that of Na current and inactivation slower still. External TEA (7.5 mM) and 4-amino-pyridine (1 mM) did not block, but 5 mM Ba blocked the K currents. K-tail currents were seen on termination of depolarizing voltage pulses. A23187 shifted the IK(V)-curve to more negative voltages. Action potentials were recorded when passing pulses of depolarizing outward current. Of the frog gustatory stimulants, 10 mM Ca caused a reversible 5- to 10-mV depolarization in the current-clamp mode. Quinine (0.1 mM, bitter) produced a reversible depolarization accompanied by a full block of Na current and, with slower time-course, a partial block of K currents. Cyclic AMP (5 mM in the external solution or 0.5 microM in the pipette) caused reversible depolarization (to -40 to -20 mV) due to partial blockage of K currents, but only if ATP was added to the pipette solution. Similar responses were elicited by stimulating the adenylate cyclase with forskolin. Blockage of cAMP-phosphodiesterase enhanced the response to cAMP. These results suggest that cAMP may be one of the cytosolic messengers in taste receptor cells. Replacement of ATP by AMP-PNP in the pipette abolished the depolarizing response to cAMP.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Amiloride-blockable sodium currents in isolated taste receptor cells.

Isolated taste receptor cells from the frog tongue were investigated under whole-cell patch-clamp conditions. With the cytosolic potential held at -80 mV, more than 50% of the cells had a stationary inward Na current of 10 to 700 pA in Ringer's solution. This current was in some cells partially, in others completely, blockable by low concentrations of amiloride. With 110 mM Na in the external and 10 mM Na in the internal solution, the inhibition constant of amiloride was (at -80 mV) near 0.3 microM. In some cells the amiloride-sensitive conductance was Na specific; in others it passed both Na and K. The Na/K selectivity (estimated from reversal potentials) varied between 1 and 100. The blockability by small concentrations of amiloride resembled that of channels found in some Na-absorbing epithelia, but the channels of taste cells showed a surprisingly large range of ionic specificities. Receptor cells, which in situ express these channels in their apical membrane, may be competent to detect the taste quality "salty." The same cells also express TTX-blockable voltage-gated Na channels.

Amiloride↗
PubMed1991

Ca(2+)-dependent chloride conductance in Necturus taste cells.

This report describes the occurrence and localization of a Ca(2+)-dependent chloride conductance in taste cells of Necturus maculosus. Lingual epithelium from Necturus was removed with blunt dissection and mounted in a modified Ussing chamber which allowed individual taste cells to be impaled with intracellular micropipettes. Solutions in the mucosal and serosal chambers could be changed independently and the properties of apical and basolateral membranes tested separately. Action potentials in taste cells, elicited by brief depolarizing current pulses passed through the intracellular recording microelectrode, provided an accurate description of whether voltage-dependent conductances had been blocked or unmasked by the experimental conditions. We found that Ca2+ influx during the action potential triggers a prolonged depolarization due to Ca(2+)-dependent conductance changes, particularly in the presence of TEA to block repolarizing K+ currents. This afterdepolarization could last up to 7 sec and is due, in part, to a Ca(2+)-dependent Cl- conductance. Other Ca(2+)-dependent channels such as Ca(2+)-dependent K+ channels or nonselective cation channels may also contribute to the afterpotential. Calcium-dependent conductance channels were situated on apical and basolateral membranes of the taste cells. We speculate that Ca(2+)-dependent Cl- channels may play a role in discriminating chloride salts from salts of other anions and may help shape receptor cell responses elicited by taste stimuli.

Action Potentials↗