Kokumi Substances, Enhancers of Basic Tastes, Induce Responses in Calcium-Sensing Receptor Expressing Taste Cells

Recently, we reported that calcium-sensing receptor (CaSR) is a receptor for kokumi substances, which enhance the intensities of salty, sweet and umami tastes. Furthermore, we found that several γ-glutamyl peptides, which are CaSR agonists, are kokumi substances. In this study, we elucidated the receptor cells for kokumi substances, and their physiological properties. For this purpose, we used Calcium Green-1 loaded mouse taste cells in lingual tissue slices and confocal microscopy. Kokumi substances, applied focally around taste pores, induced an increase in the intracellular Ca2+ concentration ([Ca2+]i) in a subset of taste cells. These responses were inhibited by pretreatment with the CaSR inhibitor, NPS2143. However, the kokumi substance-induced responses did not require extracellular Ca2+. CaSR-expressing taste cells are a different subset of cells from the T1R3-expressing umami or sweet taste receptor cells. These observations indicate that CaSR-expressing taste cells are the primary detectors of kokumi substances, and that they are an independent population from the influenced basic taste receptor cells, at least in the case of sweet and umami

The Effect of the Dried-Bonito Broth on Blood Pressure, 8-Hydroxydeoxyguanosine (8-OHdG), an Oxidative Stress Marker, and Emotional States in Elderly Subjects

Dried-bonito broth (DBB, katsuo-bushi dashi) is commonly used in Japanese cuisine, and is also used as a traditional remedy for recovery from fatigue and improvement of blood circulation. To clarify the effect of DBB on blood pressure, oxidative stress and emotional states, a randomized crossover human trial was performed. Twenty-seven elderly Japanese subjects ingested DBB or water for one month. Measurement of blood pressure and urinary 8-hydroxydeoxyguanosine (8-OHdG) and evaluation of emotional states were performed before and after the ingestion periods. The changes in systolic blood pressure (SBP) during DBB ingestion was significantly lower than that during water ingestion (p = 0.037). Urinary 8-OHdG significantly decreased during DBB ingestion (p = 0.0002). Evaluation of emotional states indicated that composure significantly improved during DBB ingestion (p = 0.034). These results suggest that the daily ingestion of DBB lower SBP, reduce urinary 8-OHdG and might improve emotional states in elderly subjects

Volatile Short-Chain Aliphatic Aldehydes Act as Taste Modulators through the Orally Expressed Calcium-Sensing Receptor CaSR

Aldehydes are natural volatile aroma compounds generated by the Maillard reaction of sugars and amino acids in food and affect the flavor of food. They have been reported to exert taste-modifying effects, such as increases in taste intensity at concentrations below the odor detection threshold. The present study examined the taste-enhancing effects of short-chain aliphatic aldehydes, such as isovaleraldehyde (IVAH) and 2-methylbutyraldehyde, thus attempting to identify the taste receptors involved. The results obtained revealed that IVAH enhanced the taste intensity of taste solutions even under the condition of olfactory deprivation by a noseclip. Furthermore, IVAH activated the calcium-sensing receptor CaSR in vitro. Receptor assays on aldehyde analogues showed that C3-C6 aliphatic aldehydes and methional, a C4 sulfur aldehyde, activated CaSR. These aldehydes functioned as a positive allosteric modulator for CaSR. The relationship between the activation of CaSR and taste-modifying effects was investigated by a sensory evaluation. Taste-modifying effects were found to be dependent on the activation state of CaSR. Collectively, these results suggest that short-chain aliphatic aldehydes function as taste modulators that modify sensations by activating orally expressed CaSR. We propose that volatile aroma aldehydes may also partially contribute to the taste-modifying effect via the same molecular mechanism as kokumi substances

Taste cell responses (ΔCa²⁺) evoked by <i>kokumi</i> stimuli, recorded in a slice preparation of the mouse circumvallate papilla.

<p>(A) Taste cells were stimulated sequentially with three <i>kokumi</i> substances, cinacalcet (CCT, 10 µM), glutathione (GSH, 100 µM) and γ-glutamyl-valinyl-glycine (γEVG, 100 µM), as well as γEVG + NPS2143 (3 µM), a CaSR antagonist. Arrowheads below traces indicate the stimulation. (B) Concentration-response relationship for γEVG (mean ± SE; n = 4 cells). (C) Taste responses elicited by γEVG (100 µM) were inhibited by the CaSR antagonist, NPS2143 (3 µM), but the umami (MPG 100 mM + IMP 1 mM) and the sweet (SC45647, 10 µM) responses were unaffected. Mean amplitudes of γEVG-, MPG + IMP-, and SC45647-induced responses in the presence or absence of 3 µM NPS2143 are shown (mean ± SE; *<i>p</i>≤0.05, n = 4 cells). Raw traces are shown in A.</p

CaSR is found in distinct cells that do not express an umami/sweet receptor subunit.

<p>(A–C) A longitudinal section of a circumvallate taste bud immunostained with antibodies against CaSR (A) and T1R3 (B). (C) Overlay of A and B. (D) A transverse section of a circumvallate taste bud immunostained with antibodies against CaSR (green) and T1R3 (red). Scale bars 20 µm.</p

Ca²⁺ response elicited by γEVG involves intracellular Ca²⁺ stores and phospholipase C.

<p>(A) γEVG (100 µM) was focally applied in medium containing Ca²⁺ (left trace) or in the absence of Ca²⁺ (Ca-free medium with 0.2 mM EGTA; right trace). (B) Responses elicited by depolarization (bath-applied KCl, 50 mM) and influx of Ca²⁺ through voltage-dependent Ca²⁺ channels were abolished in the absence of extracellular Ca²⁺. (C) Mean amplitudes of responses in the presence or absence of Ca²⁺ in the medium (mean ± SE; *<i>p</i>≤0.05, n = 4 cells). (D) Responses to γEVG inhibited by U73122 (10 µM). (E) Mean amplitudes of the responses in the presence or absence of U73122 (mean ± SE; *<i>p</i>≤0.05, n = 4 cells).</p

Taste cells express CaSR.

<p>(A) RT-PCR for <i>CaSR</i> expression in taste bud-enriched circumvallate (cv), foliate (foli) and non-taste bud (nt) lingual epithelium. nc - negative control (lacking template); M - molecular standard. (B–E) Immunostaining for CaSR in taste buds. CaSR immunofluorescence is seen in most circumvallate (B), foliate (C), palate (D) and fungiform (E) taste buds. Immunofluorescent images (green) were superimposed on DIC images. (F) Validating the anti-CaSR antibody. The CaSR antiserum was preabsorbed with an excess of antigen peptides. The circumvallate sections reacted with preabsorbed and non-absorbed antibodies and were processed simultaneously. Images were taken under the same illumination conditions and detector settings. Scale bars 20 µm.</p