PubMed Health⌕ Search

Biomedical subjects

J G Brand

Publications and source records attributed to J G Brand.

At least 19 recordsLinked to original sources
PubMed2001

Bitter taste transduced by PLC-beta(2)-dependent rise in IP(3) and alpha-gustducin-dependent fall in cyclic nucleotides.

Current evidence points to the existence of multiple processes for bitter taste transduction. Previous work demonstrated involvement of the polyphosphoinositide system and an alpha-gustducin (Galpha(gust))-mediated stimulation of phosphodiesterase in bitter taste transduction. Additionally, a taste-enriched G protein gamma-subunit, Ggamma(13), colocalizes with Galpha(gust) and mediates the denatonium-stimulated production of inositol 1,4,5-trisphosphate (IP(3)). Using quench-flow techniques, we show here that the bitter stimuli, denatonium and strychnine, induce rapid (50-100 ms) and transient reductions in cAMP and cGMP and increases in IP(3) in murine taste tissue. This decrease of cyclic nucleotides is inhibited by Galpha(gust) antibodies, whereas the increase in IP(3) is not affected by antibodies to Galpha(gust). IP(3) production is inhibited by antibodies specific to phospholipase C-beta(2) (PLC-beta(2)), a PLC isoform known to be activated by Gbetagamma-subunits. Antibodies to PLC-beta(3) or to PLC-beta(4) were without effect. These data suggest a transduction mechanism for bitter taste involving the rapid and transient metabolism of dual second messenger systems, both mediated through a taste cell G protein, likely composed of Galpha(gust)/beta/gamma(13), with both systems being simultaneously activated in the same bitter-sensitive taste receptor cell.

Animals↗
PubMed2000

Receptor and transduction processes for umami taste.

The unique taste of umami argues for a specific receptor at the taste cell level. The taste synergism between monosodium glutamate (MSG) and certain 5'-ribonucleotides provides a pharmacologic test for hypothetical mechanisms of umami taste. Early neurophysiologic and biochemical studies demonstrated specific recognition of L-glutamate by taste tissue and suggested that the synergism found with certain 5'-ribonucleotides was due to a peripheral event. The search for a receptor for umami relies at present on the data in the literature on central nervous system (CNS) glutamate receptors. These data distinguish several classes of receptors on the bases of pharmacologic properties and mode of action. Two hypotheses now seek to explain umami taste transduction. One states that umami is transduced by an N-methyl-D-aspartate (NMDA)-type glutamate ion channel receptor, the other that this taste is transduced via a metabotropic-type glutamate receptor. Evidence for the first hypothesis derives from earlier reconstitution studies, revealing a glutamate-stimulated ion channel conductance whose kinetics were affected by 5'-ribonucleotides. Additional evidence is provided from more recent calcium-imaging and patch-clamp studies, both showing that an ionotropic-type receptor on rodent taste cells mediates glutamate-induced depolarization. Evidence for the second mechanism derives from studies that located the message for an metabotropic-type (mGluR4) receptor to rat taste buds, and from whole-cell patch-clamp recordings that revealed sustained cellular conductances to glutamate and an mGluR4 agonist. It appears likely that both mechanisms are involved in umami taste transduction, suggesting the possibility that reception and transduction of the umami signal constitute a collective property of a number of cells within the taste bud.

Animals↗
PubMed1998

The arginine taste receptor. Physiology, biochemistry, and immunohistochemistry.

The amino acid, L-arginine (L-Arg), is a potent taste stimulus for the channel catfish, Ictalurus punctatus. Receptor binding studies demonstrated a high-affinity binding of L-Arg to putative taste receptor sites. This binding could be inhibited by preincubation of the tissue in the lectins Phaseolus vulgaris agglutinin (PHA) and Ricinus communis agglutinin I (RCA I). Neurophysiological studies demonstrated that the L-Arg receptor is a stimulus-gated ion channel type receptor whose conductance was stimulated by L-Arg and inhibited by D-arginine (D-Arg). To purify the receptor we subjected CHAPS solubilized partial membrane preparation from barbel epithelium to RCA I lectin affinity chromatography. The bound proteins were eluted with D-galactose. When these proteins were reconstituted into lipid bilayers, L-Arg activated single channel currents with conductances between 45 and 85 pS. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the eluted protein showed a distinct band at approximately 83 kDa. Polyclonal antibodies raised against this 83-kDa band in guinea pigs reacted with numerous small (approximately 1 micron) sites within the taste pore of every taste bud when applied to fixed nonpermeabilized barbels. This observation suggests that the antibodies recognize an externally-facing epitope of the putative Arg receptor. The antibodies also inhibited L-Arg-stimulated currents in reconstitution studies. Sephacryl S-300 HR chromatography of the eluant from the affinity column showed a high molecular weight peak (> 700 kDa) which was recognized by the antibodies. Reconstitution of the protein from this peak into a lipid bilayer resulted in L-Arg-stimulated channels that could be inhibited by D-Arg. This high molecular weight component may be aggregates of the arginine taste receptor.

Animals↗
PubMed1998

Amino acid-activated channels in the catfish taste system.

Membrane vesicles derived from external taste epithelia of channel catfish (Ictalurus punctatus) were incorporated into lipid bilayers on the tips of patch pipettes. Consistent with previous experiments (Teeter, J. H., J. G. Brand, and T. Kumazawa. 1990. Biophys. J. 58:253-259), micromolar (0.5-200 microM) concentrations of L-arginine (L-Arg), a potent taste stimulus for catfish, activated a nonselective cation conductance in some bilayers, which was antagonized by D-Arg. Two classes of L-Arg-gated receptor/channels were observed in reconstituted taste epithelial membranes: one with a unitary conductance of 40-60 pS, and the other with a conductance of 75-100 pS. A separate class of nonselective cation channels, with a conductance of 50-65 pS, was activated by high concentrations of L-proline (L-Pro) (0.1-3 mM), which is the range necessary to elicit neural responses in catfish taste fibers. The L-Pro-activated channels were not affected by either L- or D-Arg, but were blocked by millimolar concentrations of D-Pro. Conversely, neither L- nor D-Pro altered the activity of either class of L-Arg-activated channels, which were blocked by micromolar concentrations of D-Arg. These results are consistent with biochemical, neurophysiological, and behavioral studies indicating that taste responses of channel catfish to L-Arg are mediated by high-affinity receptors that are part of or closely coupled to nonselective cation channels directly gated by low concentrations of L-Arg, while responses to L-Pro are mediated by distinct, low-affinity receptors also associated with nonselective cation channels.

Amino Acids↗
PubMed1998

Cluster organization of ion channels formed by the antibiotic syringomycin E in bilayer lipid membranes.

The cyclic lipodepsipeptide, syringomycin E, when incorporated into planar lipid bilayer membranes, forms two types of channels (small and large) that are different in conductance by a factor of sixfold. To discriminate between a cluster organization-type channel structure and other possible different structures for the two channel types, their ionic selectivity and pore size were determined. Pore size was assessed using water-soluble polymers. Ion selectivity was found to be essentially the same for both the small and large channels. Their reversal (zero current) potentials with the sign corresponding to anionic selectivity did not differ by more than 3 mV at a twofold electrolyte gradient across the bilayer. Reduction in the single-channel conductance induced by poly(ethylene glycol)s of different molecular weights demonstrated that the aqueous pore sizes of the small and large channels did not differ by more than 2% and were close to 1 nm. Based on their virtually identical selectivity and size, we conclude that large syringomycin E channels are clusters of small ones exhibiting synchronous opening and closing.

Anti-Bacterial Agents↗
PubMed1998

Properties of ionic channels formed by the antibiotic syringomycin E in lipid bilayers: dependence on the electrolyte concentration in the bathing solution.

Using the planar lipid bilayer technique, organization of ionic channels formed by the lipodepsipeptide antibiotic syringomycin E applied to one (cis) side of a lipid bilayer was studied. Low concentrations of NaCl (0.01-0.1 M) induced the opening and closing of two types of channels - "small" and "large". The large channels had single channel conductances approximately six times greater than those of the small channels. An increase in the NaCl concentration (0.6-1.0 M) decreased almost completely the chance to reveal the large channels. Although the syringomycin channels exhibited the anion selectivity within the entire range of NaCl concentrations in the bathing solutions (from 0.001 to 1.0 M) whereas the concentration gradients across the bilayers were 2 and 4, the transfer numbers for Cl-decreased with an increase in the mean NaCl concentration (from 0.83 for 0.005 M to 0.70 for 0.5 M). Moreover, at each mean value of NaCl concentration, all conductance levels had the same ion selectivity (identical reversal potential). These results suggest that at low NaCl concentrations the large channels are clusters of small channels which synchronously open and close, while at high electrolyte concentrations the screening of the charged groups responsible for channel interactions prevents the cluster formation. A new theoretical approach for the estimation of the channel radius and the number of elementary charges located at its inner surface (based on the experimental curve of the dependence of transfer number on the NaCl concentration) was developed. Based on this theoretical approach, the channel radius equal to 1 nm and one elementary charge located at its inner surface were obtained.

Animals↗
PubMed1997

The effect of sterols on the sensitivity of membranes to the channel-forming antifungal antibiotic, syringomycin E.

The ability of three sterols of different structure to influence the interaction of syringomycin E (an antifungal antibiotic that forms voltage dependent channels in planar lipid bilayers) with a planar lipid bilayer was evaluated. The rate of increase of bilayer conductance induced by syringomycin E was about 1000-times less in bilayers containing 50 mol% of cholesterol compared to bilayers without sterols. The effect of ergosterol (the primary sterol of fungal cells) on the sensitivity of bilayers to syringomycin E was much weaker than that of cholesterol, while stigmasterol (one of the main sterols of plant cells) did not significantly influence the ability of syringomycin E to induce a conductance increase in the bilayer. None of the sterols altered the single channel conductance properties of syringomycin E. These observations suggest that cholesterol affects the sensitivity of target membranes to syringomycin E by enlarging the energy barrier for channel formation rather than participating in channel formation itself.

Antifungal Agents↗
PubMed1997

Selectivity and response characteristics of human olfactory neurons.

Transduction mechanisms were investigated in human olfactory neurons by determining characteristics of odorant-induced changes in intracellular calcium concentration ([Ca2+]i). Olfactory neurons were freshly isolated from nasal biopsies, allowed to attach to coverslips, and loaded with the calcium-sensitive indicator fura-2. Changes in [Ca2+]i were studied in response to exposure to individual odors, or odorant mixtures composed to distinguish between transduction pathways mediated by adenosine 3'5'-monophosphate (cAMP; mix A) or inositol 1,4,5-trisphosphate (InsP3; mix B). Overall, 52% of biopsies produced one or more odorant-responsive olfactory neurons, whereas 24% of all olfactory neurons tested responded to odorant exposure with a change in [Ca2+]i. As in olfactory neurons from other species, the data suggest that odorant exposure elicited calcium influx via second-messenger pathways involving cAMP or InsP3. Unlike olfactory neurons from other species that have been tested, some human olfactory neurons responded to odorants with decreases in [Ca2+]i. Also in contrast with olfactory neurons from other species, human olfactory neurons were better able to discriminate between odorant mixtures in that no neuron responded to more than one type of odor or mixture. These results suggest the presence of a previously unreported type of olfactory transduction mechanism, and raise the possibility that coding of odor qualities in humans may be accomplished to some degree differently than in other vertebrates, with the olfactory neuron itself making a greater contribution to the discrimination process.

Adolescent↗
PubMed1996

Differential localization of putative amino acid receptors in taste buds of the channel catfish, Ictalurus punctatus.

The taste system of catfish, having distinct taste receptor sites for L-alanine and L-arginine, is highly sensitive to amino acids. A previously described monoclonal antibody (G-10), which inhibits L-alanine binding to a partial membrane fraction (P2) derived from catfish (Ictalurus punctatus) taste epithelium, was found in Western blots to recognize a single band, at apparent MW of 113,000 D. This MW differs from the apparent MW for the presumed arginine receptor identified previously by PHA-E lectin affinity. In order to test whether PHA-E lectin actually reacts with the arginine-receptor, reconstituted membrane proteins partially purified by PHA-E affinity were used in artificial lipid bilayers. These reconstituted channels exhibited L-arginine-activated activity similar to that found in taste cell membranes. Accordingly, we utilized the PHA-E lectin and G-10 antibody as probes to differentially localize the L-alanine and L-arginine binding sites on the apical surface of catfish taste buds. Each probe labels numerous, small (0.5-1.0 micron) patches within the taste pore of each taste bud. This observation suggests that each bud is not tuned to a single taste substance, but contains putative receptor sites for both L-arginine and L-alanine. Further, analysis of double-labeled tissue reveals that the PHA-E and G-10 sites tend to be separate within each taste pore. These findings imply that in catfish, individual taste cells preferentially express receptors to either L-arginine or L-alanine. In addition, PHA-E binds to the apices of solitary chemoreceptor cells in the epithelium, indicating that this independent chemoreceptor system may utilize some receptor sites similar to those in taste buds.

Alanine↗
PubMed1996

Properties of voltage-gated ion channels formed by syringomycin E in planar lipid bilayers.

Using the planar lipid bilayer technique we demonstrate that the lipodepsipeptide antibiotic, syringomycin E, forms voltage-sensitive ion channels of weak anion selectivity. The formation of channels in bilayers made from dioleoylglycerophosphatidylserine doped with syringomycin E at one side (1-40 micrograms/ml) was greatly affected by cis-positive voltage. A change of voltage from a positive to a negative value resulted in (i) an abrupt increase in the single channel conductance (the rate of increase was voltage dependent) simultaneous with (ii) a closing of these channels and an exponential decrease in macroscopic conductance over time. The strong voltage dependence of multichannel steady state conductance, the single channel conductance, the rate of opening of channels at positive voltages and closing them at negative voltages, as well as the observed abrupt increase of single channel conductance after voltage sign reversal suggest that the change of the transmembrane field induces a significant rearrangement of syringomycin E channels, including a change in the spacing of charged groups that function as voltage sensors. The conductance induced by syringomycin E increased with the sixth power of syringomycin E concentration suggesting that at least six monomers are required for channel formation.

Anions↗
PubMed1996

Measurement of membrane potential and [Ca2+]i in cell ensembles: application to the study of glutamate taste in mice.

We have studied the spectral properties of the voltage-sensitive dye, 1-(3-sulfonatopropyl)-4-[beta [2-(di-n-octylamino)-6-naphtyl]vinyl] pyridinium betaine (di-8-ANEPPS), and the Ca(2+)-sensitive dye, fura-2, in azolectin liposomes and in isolated taste buds from mouse. We find that the fluorescence excitation spectra of di-8-ANEPPS and fura-2 are largely nonoverlapping, allowing alternate ratio measurements of membrane potential and intracellular calcium ([Ca2+]i). There is a small spillover of di-8-ANEPPS fluorescence at the excitation wavelengths used for fura-2 (340 and 360 nm). However, voltage-induced changes in the fluorescence of di-8-ANEPPS, excited at the fura-2 wavelengths, are small. In addition, di-8-ANEPPS fluorescence is localized to the membrane, whereas fura-2 fluorescence is distributed throughout the cytoplasm. Because of this, the effect of spillover of di-8-ANEPPS fluorescence in the [Ca2+]i estimate is < 1%, under the appropriate conditions. We have applied this method to study of the responses of multiple taste cells within isolated taste buds. We show that membrane potential and [Ca2+]i can be measured alternately in isolated taste buds from mouse. Stimulation with glutamate and glutamate analogs indicates that taste cells express both metabotropic and ionotropic receptors. The data suggest that the receptors responding to 2-amino-4-phosphonobutyrate (L-AP4), presumably metabotropic L-glutamate receptors, do not mediate excitatory glutamate taste responses.

Animals↗
PubMed1996

Rapid kinetics of second messenger production in bitter taste.

The tasting of bitter compounds may have evolved as a protective mechanism against ingestion of potentially harmful substances. We have identified second messengers involved in bitter taste and show here for the first time that they are rapid and transient. Using a quench-flow system, we have studied bitter taste signal transduction in a pair of mouse strains that differ in their ability to taste the bitter stimulus sucrose octaacetate (SOA); however, both strains taste the bitter agent denatonium. In both strains of mice, denatonium (10 mM) induced a transient and rapid increase in levels of the second messenger inositol 1,4,5-trisphosphate (IP3) with a maximal production near 75-100 ms after stimulation. In contrast, SOA (100 microM) brought about a similar increase in IP3 only in SOA-taster mice. The response to SOA was potentiated in the presence of GTP (1 microM). The GTP-enhanced SOA-response supports a G protein-mediated response for this bitter compound. The rapid kinetics, transient nature, and specificity of the bitter taste stimulus-induced IP3 formation are consistent with the role of IP3 as a second messenger in the chemoelectrical transduction of bitter taste.

Animals↗
PubMed1995

Capsaicin and its analogs induce ion channels in planar lipid bilayers.

The irritating, pungent compound, capsaicin (10-20 microM), induces the formation of non-selective ion channels with a wide variety of conductances in protein-free lipid bilayers form from a mixture of zwitterionic phospholipids. The channel-forming activity of capsaicin and four of its analogs followed the sequence: resiniferatoxin > capsaicin = pelargonic acid vanillylamide > methylcapsaicin >> veratrylamine. The ability to form channels correlated with the biological activity of these compounds observed in other studies that measured 45Ca uptake into rat dorsal root ganglion cells. The correlation obtained suggests that an interaction with the lipid bilayer may be an important component of the biological activity of capsaicin.

Benzylamines↗
PubMed1995

The influence of sterols on the sensitivity of lipid bilayers to melittin.

The sensitivity of planar lipid bilayers to the permeabalizing effect of melittin was evaluated when sterols of varying structure were incorporated into the membrane. The addition of increasing amount of cholesterol (0-50 mole %) decreased the sensitivity of membranes formed from negatively charged phospholipids to melittin but did not (in amount of up to 66 mole %) change the sensitivity of membranes formed from zwitterionic lipids. 7-Dehydrocholesterol, stigmasterol and ergosterol had the same ability as that of cholesterol to decrease the membrane sensitivity to melittin, while lanosterol had no effect on the sensitivity of membranes to melittin. The results suggest that the effect of sterols is complex and cannot be explained only by a direct interaction of melittin with cholesterol, by a decrease of membrane fluidity, or by changes in distribution of surface charge.

Cholesterol↗
PubMed1995

Functionally mature olfactory neurons from two anosmic patients with Kallmann syndrome.

Patients with Kallmann syndrome (KS) exhibit hypogonadotropic hypogonadism and anosmia [Kallmann et al., Am. J. Mental Def., 48 (1944) 203-236] secondary to failure of gonadotropin-releasing hormone (GnRH)-producing neurons to migrate from the olfactory placode to the brain, and to agenesis of the olfactory bulbs. It has been hypothesized that olfactory neurons (ON) from individuals with KS are immature partly on the basis of studies in animals showing that lack of synaptic connection of ON with the olfactory bulb results in expression of immature ON [Schwob et al., J. Neurosci., 12 (1979) 880-883]. To test this assumption, we obtained olfactory tissue samples from two males diagnosed with KS on the basis of medical history and MRI studies. Both patients were anosmic. The functioning of cells isolated from biopsies taken from the upper middle turbinate and septum was studied by measuring changes in intracellular Ca2+ concentration ([Cai]) using dual excitation fluorescence microscopy. Biopsies from both patients yielded cells that morphologically appeared to be ON. Seven of 16 cells that morphologically resembled ON responded with a change in [Cai] upon stimulation with an odorant mixture. These studies show that at least some ON in KS individuals are functionally mature and suggest that complete development of the olfactory bulbs is not required for differentiation of mature human ON.

Adolescent↗
PubMed1995

The properties of ion channels formed by the coumarin antibiotic, novobiocin, in lipid bilayers.

The coumarin antibiotic novobiocin forms ion channels of varying conductances in lipid bilayers. The conductances (about 20, 22, 14, 7 and 2 pS for 100 mM NH4Cl, CsCl, KCl, NaCl and LiCl, respectively) and selectivities (cation transference numbers in the range of 0.97-0.98) of one type of novobiocin-induced channel are similar to those found for channels formed by gramicidin A, an antibiotic of very different structure. The conductance of novobiocin channels of this type was independent of the species of the membrane lipid. This observation suggests that novobiocin molecules directly form these channels, and that channels are not formed through defects in lipid structure. The similarity in conductance and ion selectivity between channels induced by novobiocin and those formed by gramicidin A suggests that these structurally different molecules form channels with comparable internal diameter and internal surface charge distribution. Using HPLC purification we argue that the channel-forming activity of novobiocin is related to the activity of the novobiocin molecule itself, and not to a contaminant of the commercially available novobiocin sodium salt preparation.

Cations, Monovalent↗
PubMed1994

Generation of inositol phosphates in bitter taste transduction.

It is probable that there is a diversity of mechanisms involved in the transduction of bitter taste. One of these mechanisms uses the second messengers, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). Partial membrane preparations from circumvallate and foliate taste regions of mice tongues responded to the addition of known bitter taste stimuli by increasing the amount of inositol phosphates produced after 30 s incubation. Addition of both the bitter stimulus, sucrose octaacetate and the G-protein stimulant, GTP gamma S, led to an enhanced production of inositol phosphates compared with either alone. Pretreatment of the tissue samples with pertussis toxin eliminated all response to sucrose octaacetate plus GTP gamma S, whereas pretreatment with cholera toxin was without effect. Western blots of solubilized tissue from circumvallate and foliate regions probed with antibodies to the alpha-subunit of several types of G-proteins revealed bands reactive to antibodies against G alpha i1-2 and G alpha o, with no apparent activity to antibodies against G alpha i3. Given the results from the immunoblots and those of the toxin experiments, it is proposed that the transduction of the bitter taste of sucrose octaacetate in mice involves a receptor-mediated activation of a Gi-type protein which activates a phospholipase C to produce the two second messengers, IP3 and DAG.

Animals↗