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At least 1,711 records · Page 95Linked to original sources
PubMed1985

Inhibition by amiloride of chorda tympani responses evoked by monovalent salts.

The diuretic, amiloride, is a potent yet reversible inhibitor of passive sodium transport in many epithelia. It has been shown to inhibit sodium transport in dorsal lingual epithelia and to inhibit both psychophysical and neural measures of salt taste. The present results demonstrate that amiloride's action as an inhibitor of integrated whole chorda tympani nerve recordings in the rat is specific for Li and Na salts, displaying little inhibition of neural responses evoked by KCl and RbCl. Amiloride reduces both the phasic and tonic portion of the nerve recording equally. When amiloride inactivates the tonic portion of the nerve response to 250 mM NaCl, only a portion of the response is affected. Complete inactivation does not occur even at high amiloride concentrations. With amiloride flowing constantly over the tongue at 1 microM, 10 microM, or 50 microM a reciprocal plot of stimulus NaCl concentration versus response is non-linear. This result suggests that the inhibition of the NaCl-induced response has both competitive and non-competitive properties. These results support the hypothesis that salt taste is mediated in part by amiloride sensitive Na-channels located in taste receptor cell plasma membranes.

Amiloride↗
PubMed1985

Response characteristics of three taste nerves in mice.

Gustatory responses from 3 nerves, the chorda tympani, glossopharyngeal and superior laryngeal nerves were investigated in the mouse. Stimuli were NH4Cl, NaCl, KCl, HCl, quinine-HCl, sucrose, urea, glucose and distilled water. The 3 nerves responded differently to these stimuli. The chorda tympani responded strongly to HCl and sucrose, but weakly to quinine-HCl, while the glossopharyngeal responded well to quinine-HCl rather than to either HCl or sucrose. The order of effective stimulation was NH4Cl greater than NaCl greater than KCl for the chorda tympani, whereas NH4Cl greater than KCl greater than NaCl for the glossopharyngeal nerve. The responses of the superior laryngeal nerve were remarkably different from those of the others. Water was the most effective stimulus for the nerve and the response to water was depressed by either electrolytes or non-electrolytes added in water. These results suggest dissimilar contributions of the 3 nerves to the physiological functions.

Animals↗
PubMed1986

Salt taste responses in the frog glossopharyngeal nerve: different receptor sites for Mg2+ and Na+.

The glossopharyngeal nerve of the frog responds to MgCl2 and NaCl applied to the tongue. To learn whether or not Mg2+ and Na+ react with different receptor sites, a proteolytic enzyme was topically applied to the tongue dorsum. Responses were recorded from the frog glossopharyngeal nerve during stimulation of the tongue with 100 mM MgCl2 and 500 mM NaCl. The magnitude of the MgCl2 response was selectively reduced after application of 0.1% pronase E to the dorsal tongue surface. The selective suppression of the MgCl2 response by the pronase treatment indicates that the receptor site responsible for the MgCl2 response differs from that for the NaCl response. The effect of pronase on the MgCl2 response was due to the proteolytic action. This suggests that the receptor site responsible for the MgCl2 response is composed of a protein or interacts secondarily with a protein affected by pronase treatment. It is suggested that there are multiple receptor sites for cations in salt taste reception of the frog.

Animals↗
PubMed1987

Differential interaction of lectins with chemosensory receptors.

L-Alanine and L-arginine bind with similar affinity (Kd 10(-7)-10(-6) M) to receptors in both a sedimentable fraction (P2) from taste epithelium and isolated olfactory cilia from the channel catfish, Ictalurus punctatus. Lectins of differing carbohydrate specificity were used to determine the glycoprotein nature of the chemosensory plasma membranes and to differentially affect receptors for L-alanine and L-arginine. The peroxidase-conjugated lectins concanavalin A (Con A), wheat germ agglutinin (WGA), and peanut agglutinin (PNA) were used to identify the glycoprotein components of the chemosensory plasma membranes after polyacrylamide gel electrophoresis. In both chemosensory membranes, numerous protein components were labelled by Con A and WGA. In contrast, a single predominant component was labeled by PNA in olfactory cilia, whereas several proteins in taste membranes were labeled by this lectin. When unconjugated lectins were preincubated with olfactory cilia, 60-70% of binding to L-alanine and L-arginine receptors was inhibited by Con A and WGA. PNA inhibited L-alanine but not L-arginine binding to olfactory receptors. Inhibition of olfactory receptor binding by lectins was time- and dose-dependent. By contrast, no inhibition of either L-alanine or L-arginine receptor binding in taste membranes was observed with any of the lectins. The differential labeling of the chemosensory membranes and the differential inhibition of receptor binding by lectins suggest that, despite ligand similarity, the chemosensory receptors in these membranes are not identical molecular species.

Alanine↗
PubMed1987

Membrane properties of glossopharyngeal sensory neurons in the petrosal ganglion of the cat.

The active and passive properties of petrosal ganglion sensory neurons with axons in the glossopharyngeal nerve were examined with intracellular microelectrodes in an in vitro preparation. Glossopharyngeal neurons could be classified into two groups: H-cells showing an inflexion or hump on the falling phase of the spike and F-cells, generating a short action potential without a hump. Most of the neurons found (85%) were H-cells. The axonal conduction velocity of both types of cells fell into the A delta range, although the average value for F-cells (13 m/s) was higher than that found for H-cells (10 m/s). H- and F-cells had similar resting membrane potentials and input resistances, but different action potential characteristics. F-cells showed a smaller action potential with a faster rate of depolarization, followed by a shorter after-hyperpolarization. The response to depolarizing current pulses applied through the microelectrode was also different in both types of cells. About half of the H-cells could not be depolarized to threshold while 85% of F-cells generated spikes. It is concluded that two different populations of petrosal ganglion neurons send axons into the glossopharyngeal nerve.

Action Potentials↗
PubMed1988

Membrane properties of isolated frog taste cells: three types of responsivity to electrical stimulation.

The whole cell clamp technique was applied to an isolated frog taste cell to examine the detailed membrane properties. The electrical responses could be classified into 3 types. The taste cells of the active type generated a large spike potential under current clamp and a large early inward current followed by a small outward current. The taste cells of the inactive type did not generate a spike but showed a small inward current followed by a large outward current. The distribution of each type was 15, 70 and 15%, respectively.

Animals↗
PubMed1988

Voltage- and current-clamp recordings of the receptor potential in mouse taste cell.

Intracellular recordings were obtained using the current-clamp and voltage-clamp techniques. When the taste cell membrane was voltage-clamped, the sucrose stimulus induced an inward current accompanied by a membrane resistance increase while the NaCl stimulus induced an inward current accompanied by a membrane resistance decrease. These phenomena indicated that sucrose and NaCl have quite a different generation mechanism of taste responses.

Animals↗
PubMed1989

Specific L-arginine taste receptor sites in the catfish, Ictalurus punctatus: biochemical and neurophysiological characterization.

We report here the characterization of the arginine binding site(s) and corroborative neurophysiological studies. Binding of L-[3H]arginine to Fraction P2 from taste epithelium was measured by a modification of the method of Krueger and Cagan. Parameters for measuring maximal binding activity were established for both duration of incubation and pH of medium. At pH 7.8, the apparent single rate constant for association (kobs) at 4 degrees C was 4.72 x 10(+5).M-1.min-1. Dissociation was more complex, yielding two rate constants of 1.77.min-1 and 8.34 x 10(-3).min-1. These data suggest the presence of two affinity states for L-arginine. The KD values as calculated from the ratio k-1/k+1 were 1.3 x 10(-6) M and 1.8 x 10(-8) M. Homologous inhibition studies of L-arginine binding were not fit by a simple mass action relationship (Hill Coefficient 0.79), but were best fit by a two-site model with IC50 values of 1.6 x 10(-6) M for the high affinity state and 9 x 10(-4) M for the low affinity state. Multiunit neural recordings examined the stimulatory effectiveness of a number of guanidinium-containing compounds. Compared with L-arginine, only L-arginine methyl ester and L-alpha-amino-beta-guanidino propionic acid (L-AGPA) were effective stimuli. Cross-adaptation experiments demonstrated that at 10(-4) M L-arginine methyl ester, L-AGPA and, to a lesser extent, D-arginine were effective cross-adapting stimuli to 10(-6) M L-arginine. In competition binding studies L-arginine methyl ester, L-AGPA and D-arginine also inhibited binding of L-[3H]arginine (10(-6) M), but each recognized only one affinity state. Inhibition by the poorly cross-adapting stimuli L-glutamate, glycine and L-alanine occurred only above 10(-3) M, indicating that the binding sites for L-arginine are selective. These studies suggest that there are at least two affinity states of L-arginine binding, that the binding sites are specific, and that effective agonists of L-arginine receptors must contain a guanidinium group and an unblocked L-alpha-amino group.

Animals↗
PubMed1992

Cross-adapted salt responses in the mouse taste cell.

The exact nature of taste adaptation is not known. Intracellular recordings from taste receptor cells are appropriate to clarify cellular adaptation properties. I approached the study of the sugar and salt receptor mechanisms of mammalian taste cells with cross-adaptation experiments. Sucrose pre-adaptation suppresses the cross-adaptation responses to salts. The results show that the taste adaptation is located in the taste receptor cell.

Adaptation, Physiological↗
PubMed1992

Functional regeneration of glossopharyngeal nerve through micromachined sieve electrode arrays.

To assess the potential of micromachined silicon sieve electrodes for long term recordings from single afferent sensory fibers, we implanted them between the cut ends of rat glossopharyngeal nerves which innervate taste and somatosensory receptors on the posterior tongue. After the implants had been in place for an average of 101 days nerve regeneration was measured using histological and electrophysiological methods. Axons of the glossopharyngeal nerve regenerated through holes in the sieves and supported the functional regeneration of taste, thermal and mechanoreceptors.

Animals↗
PubMed1995

Electrophysiological characterization of the inhibitory effect of a novel peptide gurmarin on the sweet taste response in rats.

The effect of an anti-sweet peptide, gurmarin purified from the leaves of Gymnema sylvestre, was studied electrophysiologically on taste responses of the rat chorda tympani. The action of gurmarin was highly specific to sweet taste so that responses to various sweeteners including sugars, sweet amino acids and an artificial sweetener, saccharin were all suppressed. The most effective pH at which the rat tongue was treated with gurmarin was found to be 4.5, which corresponds to the isoelectric point of the peptide. At this condition about 5 microM of gurmarin was sufficient to reveal maximal effect and this was still significant at 0.5 microM (2 micrograms/ml). Although the suppressed responses required several hours to attain complete recovery, anti-gurmarin serum shortened the recovery time considerably. On the other hand, intravenous injection of gurmarin did not cause any significant effects on taste responses at all. These results suggest that gurmarin acts on the apical side of the taste cell, possibly by binding to the sweet taste receptor protein.

Amino Acids↗
PubMed1996

Properties of Na(+)-dependent K+ conductance in the apical membrane of frog taste cells.

Na(+)-dependent K+ conductance observed in apical membrane of isolated bullfrog taste cells was analyzed using various modifications of the patch clamp method. When the apical receptive membrane of a taste cell was exposed to 0.5 M NaCl using a pipette perfusion method, an inward current appeared in the cell-attached patch membrane. The permeability ratio of Na+ to K+ (P(Na)/P(K)) calculated from the reversal potential was 0.3. When an outside-out patch from the receptive membrane was exposed to 0.25 M NaCl solution, two types of K+ channel, whose conductance were 35.8 and 9.4 pS respectively, were activated. These channels were reversibly activated by increasing internal Na+ concentration. In the whole cell configuration, the outward current evoked by a voltage ramp from -80 to 80 mV was significantly suppressed by replacement of Na+ by N-methyl-D-glucamine+ (NMDG+). The Na(+)-dependent outward current was blocked by 10 mM BaCl2, with positive shift of the zero-current potential in the whole cell recordings, indicating that the outward current including Na(+)-dependent K+ component contributes to maintenance of the resting potential. These results suggest that small conductance Na(+)-dependent K+ channels, which are also permeable to Na+, are involved in salt signal transduction in frog taste cells.

Animals↗
PubMed1989

Genetic control of sexually dimorphic axon morphology in Drosophila sensory neurons.

The mechanism by which orderly axonal projections are formed during development remains an important and largely unsolved problem in neurobiology. It may be possible to examine the control of axon growth in Drosophila and take advantage of genetic tools to better understand the phenomenon. We show here that some gustatory axons in Drosophila are sexually dimorphic and that genes involved in sex determination control the anatomy of these axons. Both males and females possess gustatory receptors on their legs but males possess more of these receptors than females. More significantly, the axons of the male receptors usually cross the midline and they never do so in females, indicating a central zone of bilateral input in the male but not in the female nervous system. In chromosomal females, expressing a tra or Sxl mutation, the gustatory system is transformed toward the male phenotype. Mutant XX adults resemble normal males externally, because they have more gustatory receptors, and internally, because their axons cross the midline. Gynandromorphs show that the sex of the sensory neuron, and apparently not the central nervous system, controls the growth of the axons. We conclude that the anatomical site of control for this dimorphism is the gustatory neurons.

Animals↗