Biomedical subjects

Fang-Li Zhao

Publications and source records attributed to Fang-Li Zhao.

4 recordsLinked to original sources

PubMed2004

A paracrine signaling role for serotonin in rat taste buds: expression and localization of serotonin receptor subtypes.

Recent advances in peripheral taste physiology now suggest that the classic linear view of information processing within the taste bud is inadequate and that paracrine processing, although undemonstrated, may be an essential feature of peripheral gustatory transduction. Taste receptor cells (TRCs) express multiple neurotransmitters of unknown function that could potentially participate in a paracrine role. Serotonin is expressed in a subset of TRCs with afferent synapses; additionally, TRCs respond physiologically to serotonin. This study explored the expression and cellular localization of serotonin receptor subtypes in TRCs as a possible route of paracrine communication. RT-PCR was performed on RNA extracted from rat posterior taste buds with 14 prime sets representing 5-HT(1) through 5-HT(7) receptor subtype families. Data suggest that 5-HT(1A) and 5-HT(3) receptors are expressed in taste buds. Immunocytochemistry with a 5-HT(1A)-specific antibody demonstrated that subsets of TRCs were immunopositive for 5-HT(1A). With the use of double-labeling, serotonin- and 5-HT(1A)-immunopositive cells were observed exclusively in nonoverlapping populations. On the other hand, 5-HT(3)-immunopositive taste receptor cells were not observed. This observation, combined with other data, suggests 5-HT(3) is expressed in postsynaptic neural elements within the bud. We hypothesize that 5-HT release from TRCs activates postsynaptic 5-HT(3) receptors on afferent nerve fibers and, via a paracrine route, inhibits neighboring TRCs via 5-HT(1A) receptors. The ole of the 5-HT(1A)-expressing TRC within the taste bud remains to be explored.

Animals↗

PubMed2002

Expression and physiological actions of cholecystokinin in rat taste receptor cells.

Gustatory perception arises not only from intracellular transduction cascades within taste receptor cells but also from cell-to-cell communication among the cells of the taste bud. This study presents novel data demonstrating that the brain-gut peptide cholecystokinin (CCK) is expressed in subsets of taste receptor cells, and that it may play a signaling role unknown previously within the taste bud. Immunocytochemistry revealed positively stained subsets of cells within taste buds throughout the oral cavity. These cells typically displayed round nuclei with full processes, similar to those classified as light cells. Peptide expression was verified using nested PCR on template cDNA derived from mRNA extracted from isolated posterior taste buds. Multiple physiological actions of cholecystokinin on taste receptor cells were observed. An outward potassium current, recorded with the patch-clamp technique, was inhibited by exogenous application of sulfated cholecystokinin octapeptide in a reversible and concentration-dependent manner. Pharmacological analysis suggests that this inhibition is mediated by CCK-A receptors and involves PKC phosphorylation. An inwardly rectifying potassium current, typically invariant to stimulation, was also inhibited by cholecystokinin. Additionally, exogenous cholecystokinin was effective in elevating intracellular calcium as measured by ratiometric techniques with the calcium-sensitive dye fura-2. Pharmacology similarly demonstrated that these calcium elevations were mediated by CCK-A receptors and were dependent on intracellular calcium stores. Collectively, these observations suggest a newly discovered role for peptide neuromodulation in the peripheral processing of taste information.

Animals↗

PubMed2002

Adrenergic signalling between rat taste receptor cells.

In taste buds, synaptic transmission is traditionally thought to occur from taste receptor cells to the afferent nerve. This communication reports the novel observation that taste receptor cells respond to adrenergic stimulation. Noradrenaline application inhibited outward potassium currents in a dose-dependent manner. This inhibition was mimicked by the beta agonist isoproterenol and blocked by the beta antagonist propranolol. The alpha agonists clonidine and phenylephrine both inhibited the potassium currents and elevated intracellular calcium levels. Inwardly rectifying potassium currents were unaffected by adrenergic stimulation. Experiments using the RT-PCR technique demonstrate that lingual epithelium expresses multiple alpha (alpha1a, alpha1b, alpha1c, alpha1d, alpha2a, alpha2b, alpha2c) and beta (beta1, beta2) subtypes of adrenergic receptors, and immunocytochemistry localized noradrenaline to a subset of taste receptor cells. Collectively, these data imply strongly that adrenergic transmission within the taste bud may play a paracrine role in taste physiology.

Adrenergic alpha-Agonists↗

PubMed2002

Dual actions of caffeine on voltage-dependent currents and intracellular calcium in taste receptor cells.

Although the numerous stimuli representing the taste quality of bitterness are known to be transduced through multiple mechanisms, recent studies have suggested an unpredicted complexity of the transduction pathways for individual bitter stimuli. To investigate this notion more thoroughly, a single prototypic bitter stimulus, caffeine, was studied by using patch-clamp and ratiometric imaging techniques on dissociated rat taste receptor cells. At behaviorally relevant concentrations, caffeine produced strong inhibition of outwardly and inwardly rectifying potassium currents. Caffeine additionally inhibited calcium current, produced a weaker inhibition of sodium current, and was without effect on chloride current. Consistent with its effects on voltage-dependent currents, caffeine caused a broadening of the action potential and an increase of the input resistance. Caffeine was an effective stimulus for elevation of intracellular calcium. This elevation was concentration dependent, independent of extracellular calcium or ryanodine, and dependent on intracellular stores as evidenced by thapsigargin treatment. These dual actions on voltage-activated ionic currents and intracellular calcium levels suggest that a single taste stimulus, caffeine, utilizes multiple transduction mechanisms.

Action Potentials↗