Physiological studies on umami taste

The first electrophysiological studies on umami taste were conducted with rats and cats. Unlike humans, these animals did not show a large synergism between monosodium glutamate (MSG) and disodium guanylate (GMP) or disodium inosinate (IMP). The taste nerve responses of these animals to umami substances were not differentiated from the salt responses. The canine taste system was sensitive to umami substances and showed a large synergism between MSG and GMP or IMP. The umami substances showed no enhancing effects on other basic tastes. Amiloride, an inhibitor for the response to NaCl, did not inhibit the large response induced by the synergism between MSG and the nucleotides, indicating that the response to the umami substances is independent of the response to salt. Single-fiber analysis on the responses of mouse glossopharyngeal nerve and monkey primary taste cortex neurons also showed that the responses to umami substances are independent of other basic tastes. On the basis of these results, it was proposed that the umami taste is a fifth basic taste, and that there is a unique receptor for umami substances. Hence, we compared the taste of agonists for brain glutamate receptors. In humans, the order of intensity of umami taste induced by a mixture of 0.5 mmol/L GMP and 1.5 mmol/L of various agonists was glutamate > ibotenate > L(+)-2-amino-4-phosphonobutyric acid (L-AP4) = (+/-)1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD). Kainate, N-methyl-D-aspartic acid (NMDA) and (RS)-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), which are agonists for ionotropic receptors, had no umami taste. It was concluded that the umami receptor is not identical to any known glutamate receptors; there seems, therefore, to be a unique receptor for umami.

Trapezoid bone fracture

Fractures of the carpal bones involve only a single bone or complex bones with or without ligament rupture. However, fractures of the trapezoid are rarely seen. Because the trapezoid is fastened to the trapezium, capitate, and scaphoid by strong ligaments, fracture or dislocation is limited by this rigid fixation. The authors present a single bone fracture of the trapezoid in a 40-year-old man. A tomogram of the carpal bone was useful in diagnosing the trapezoid fracture. The mechanism for development of fracture of the trapezoid alone is unknown. However, fracture of the trapezoid seemed to occur when the wrist joint was forced with excessive flexion stress that was placed on the trapezoid through the second metacarpal bone indirectly. This occurred in the same manner that a walnut is broken with nutcrackers.

Osteochondroma of the mandibular body

We have treated four cases of osseous ostechondromas arising on the mandibular body, where this tumor rarely presents on the craniomaxillofacial bones. There were no recurrences after simple surgical resection of these tumors.

Analysis of promoter activity of 5'-upstream regions of zebrafish olfactory receptor genes

The vertebrate olfactory system receives and discriminates a great variety of odorants. Many lines of evidence suggest that individual olfactory neuron expresses a single type or limited types of the olfactory receptor genes. However, the mechanism of selection of a single gene in the olfactory receptor family remains unclear. In the present study, we utilized zebrafish to identify the promoter element of the olfactory receptor genes in their 5'-upstream regions. First, we isolated a number of zebrafish olfactory receptor genes. These olfactory receptor genes were specifically expressed in the olfactory tissue as visualized by whole mount in situ hybridization analysis. Time of onset of the expression of each receptor clone varied from 24 h to 48 h postfertilization. Then, we injected various constructs containing the 5'-upstream regions of the olfactory receptor genes connected to beta-galactosidase reporter gene into fertilized zebrafish embryos. Constructs from two independent olfactory receptor genes exerted beta-galactosidase (promoter) activity that is specifically upregulated in the olfactory tissue. Use of either longer or deleted constructs of these two genes diminished the promoter activity in the olfactory tissue. From these results we discuss the mechanism of the transcription of the olfactory receptor genes in the olfactory neurons.

Characterization of a phosphorylation event resulting in upregulation of the salivary Na(+)-K(+)-2Cl(-) cotransporter

Previous studies from our laboratory have shown a close correlation between increased Na(+)-K(+)-2Cl(-) cotransporter activity and increased cotransporter phosphorylation after beta-adrenergic stimulation of rat parotid acinar cells. We demonstrate here that these effects are paralleled by an increase in the number of high-affinity binding sites for the cotransporter inhibitor bumetanide in membranes prepared from stimulated acini. We also show that the sensitivity of cotransporter fluxes to inhibition by bumetanide is the same in both resting and isoproterenol-stimulated cells, consistent with the hypothesis that beta-adrenergic stimulation and the accompanying phosphorylation result in the activation of previously quiescent transporters rather than in a change in the properties of already active proteins. In addition, we demonstrate that the increased phosphorylation on the cotransporter resulting from beta-adrenergic stimulation is localized to a 30-kDa phosphopeptide obtained by cyanogen bromide digestion. Immunoprecipitation and Western blotting experiments demonstrate that this peptide is derived from the NH(2)-terminal cytosolic tail of the cotransporter, which surprisingly does not contain the sole protein kinase A consensus site on the molecule.

Risk factors and triggers of sudden death in the working generation: an autopsy proven case-control study

In Japan, studies on the risk factors of sudden death in the working generation have been rarely carried out, especially among extremely rare cases of causative disease. Thus, the present study aimed to identify the risk factors and triggers of sudden death in cases whose causes of death were definitely proven by autopsy. We investigated the legal medical records for four years from May 1994 to February 1998. Out of 271 cases, 176 patients 20 to 59 years were enrolled as cases of sudden death in the working generation. Among these, 91 cases, 52%, could be analyzed by telephone interviews from close family members. Only one examiner undertook all phone questions to the case subjects. As control subjects, 1167 persons who consulted us for a health check were employed. Of the sudden death cases, the final diagnosis in 29 cases was coronary artery disease (31.9%), 18, acute cardiac dysfunction (19.8%), 6, other cardiac diseases (6.6%), 4, acute aortic dissection (4.4%), 4, cerebrovascular disease (4.4%) and 30, other diseases (32.9%). Through conditional logistic analysis, the following risk factors emerged as candidates: Long-term stress, history of heart disease, hypertension, chest symptoms, autonomic disturbance, short-term stress and a smoking habit. Short-term stress, autonomic disturbance and a smoking habit increased the risk of sudden death due to coronary artery disease. Long-term stress was associated with an increased risk of sudden death due to acute cardiac dysfunction. It was also demonstrated that autonomic disturbance and stress were closely related to the occurrence of sudden death. Therefore, to prevent sudden death, it would be helpful to identify subjective symptoms to relieve such stress in some way.

How many biopsies should be performed during percutaneous transhepatic cholangioscopy to diagnose biliary tract cancer?

BACKGROUND

The sensitivity of biopsy in the diagnosis of cholangiocarcinoma using percutaneous transhepatic cholangioscopy is not well defined.

METHODS

Patients with a biliary tract malignancy (n = 52) underwent directed biopsy during percutaneous transhepatic cholangioscopy using a 1.8 mm diameter forceps. Histologic findings were correlated with endoscopic appearance.

RESULTS

A diagnosis of carcinoma was made in all four patients with a tumor of the major duodenal papilla and in all 15 patients with a polypoid bile duct tumor with two biopsies from the mass. In 19 patients with stenotic bile duct cancer, a positive diagnosis was made in 95% of cases when three biopsies were taken from the margin of the stenotic area. When cholangioscopy showed a tortuous, dilated vessel (n = 10), the diagnosis of cancer was made with two biopsies taken from the margin of the stenosis. In 14 patients with metastatic bile duct cancer, the diagnosis was made in only 43% of cases when three biopsies were taken from the margin of the stenosis. When combined with results from the three biopsies taken from within the area of stenosis, the sensitivity for diagnosing pancreatic cancer improved from 20% to 60%.

CONCLUSIONS

Directed cholangioscopic biopsies are highly sensitive for the diagnosis of cholangiocarcinoma but less sensitive for cancer metastatic to the bile duct. The numbers and locations of the biopsies required to make a diagnosis of carcinoma depend on the origin and cholangioscopic appearance of the tumor.

Macrocystic schwannoma in the seventh cervical nerve

We have recently treated a case of asymptomatic macrocystic schwannoma discovered between the left neck and the supraclavicular fossa. The tumor, originating from the left seventh cervical nerve, was extirpated. Nearly 70 percent of the tumor area showed macrocyst with transparent fluid collection. The tumor was diagnosed as macrocystic schwannoma histopathologically. Schwannoma is often associated with small cysts but rarely with macrocysts. Because schwannoma is a benign tumor, partial resection against an attempt at total removal resulting in progressive neurologic deficits is recommended. In general, schwannoma does not present any apparent symptoms at an early stage, because it occurs and progresses very slowly. Schwannoma originating at the spinal nerve root has been called a dumbbell-shaped tumor because of its characteristic shape on MRI and cystogram images. We recently have treated a case of dumbbell-shaped tumor that was an asymptomatic macrocystic schwannoma in the seventh cervical nerve.

Purification and characterization of membrane-bound prostaglandin E synthase from bovine heart

Prostaglandin (PG) E synthase was solubilized with 6 mM sodium deoxycholate from the microsomal fraction of bovine hearts. The enzyme was purified by about 800-fold to apparent homogeneity. The specific activity of the purified enzyme was about 830 mU/mg of protein, and the K(m) value for PGH(2) was 24 microM. The molecular weight of the enzyme was about 31000 on SDS-polyacrylamide gel electrophoresis and was about 60000 by gel filtration. The enzyme was separated from glutathione (GSH) S-transferase by DEAE-Toyopearl column chromatography, and did not exhibit any GSH S-transferase activity towards four different substrates. The purified enzyme was active in the absence of GSH, but it was activated by various SH-reducing reagents including dithiothreitol, GSH, or beta-mercaptoethanol. This is the first reported purification of membrane-bound PGE synthase to apparent homogeneity.

The residual epiretinal membrane after vitrectomy for macular hole

BACKGROUND

We retrospectively observed idiopathic macular holes in 63 eyes using a scanning laser ophthalmoscope, in order to study the relation between postoperative epiretinal membranes and closure of macular holes following vitrectomy.

METHODS

The eyes were classified into three groups based on the degree of the postoperative epiretinal membranes. Group I consisted of 23 eyes with no epiretinal membrane remaining on the retina after vitrectomy. Group II consisted of 20 eyes in which epiretinal membranes were observed on the retina, but separate from the edge of the macular hole. Group III consisted of 20 eyes in which epiretinal membranes were observed at the edge of the macular hole. Using these three groups, we studied how postoperative epiretinal membranes were related to the closure of macular holes.

RESULTS

All macular holes (100%) in groups I and II were closed following vitrectomy. In group III, 5 (25.0%) of 20 eyes had complete closure and 13 eyes (65.0%) had incomplete closure of the macular hole, while 2 eyes (10.0%) had re-opening of initially closed macular holes several months after vitrectomy.

CONCLUSION

Residual postoperative epiretinal membranes at the edge of macular hole are responsible for primary failure of vitrectomy. Removal of epiretinal tissues around the macular hole is important for macular hole to be closed following vitrectomy.

Synthesis and structure-activity relationships of new non-steroidal progesterone receptor ligands

In order to study structure-activity relationships, a series of new non-steroidal progesterone receptor ligands based on PF1092A was synthesized with structural modifications (mostly introduction or removal of a methyl group) at the 3-, 4-, 5-, 7- or 9-position in the 6-acetoxy-4a, 5, 6, 7-tetrahydro-3, 4a, 5-trimethylnaphtho[2,3-b]furan-2(4H)-one skeleton. Critical positions for high binding affinity to the progesterone receptor were identified.

Modulation of thyroid hormone-dependent Na+,K(+)-ATPase induction in cultured human submandibular gland cell lines, HSG cells

The hormonal regulation of Na+,K(+)-ATPase enzyme activities and induction of the alpha subunit protein of the enzyme in the human submandibular gland (HSG) were studied by use of cultured HSG cells. We treated HSG cells with thyroid hormone, androgen, mineralocorticoid, and glucocorticoid, singly or in combination. 3,5,3'-Triiodothyronine (T3), 5 alpha-dihydrotestosterone (DHT), and aldosterone (Ald) induced neither Na+,K(+)-ATPase enzyme activity nor its protein. On the other hand, dexamethasone (Dex) induced both Na+,K(+)-ATPase enzyme activity and the alpha subunit protein level to 128% of the control. The effects of Dex in combination with either T3 or DHT were similar to the effect of Dex alone. Treatment in combination with Dex and Ald increased the enzyme activity and alpha subunit protein level to 160%, synergistically. These increased Na+,K(+)-ATPase enzyme activities were shown to be dependent on their protein levels induced by the hormones. Contrary to the previous evidence that Na+,K(+)-ATPase of ducts in the salivary gland are thyroid hormone inducible, HSG cells had an insignificant response to thyroid hormone in the present study. Also, Na+,K(+)-ATPase enzyme activity and its alpha subunit protein were not induced by any kind of combined treatments with T3. Furthermore, T3 did not cause intracellular calcium mobilization in HSG cells. In view of all data taken together, we suggest that HSG cells lack the thyroid hormone receptor, which is necessary for Na+,K(+)-ATPase induction in human salivary gland.

Regionalization of Fos immunostaining in rat accessory olfactory bulb when the vomeronasal organ was exposed to urine

The distribution of Fos-immunoreactive (Fos-ir) cells in the accessory olfactory bulb (AOB) of rats following vomeronasal organ exposure to urine was studied. Following exposure to male and female Wistar rat urine, Fos-ir cells were found in the mitral/tufted cell layer, granule cell layer and periglomerular cell layer of the AOB of female Wistar rat, with the highest number in the granule cell layer. Exposure to water or removal of the vomeronasal organ suppressed the expression of Fos-ir cells. These results suggest that female Wistar rats specifically detect urinary substances derived from male or female Wistar rats via the vomeronasal organ. Exposure of the vomeronasal organ of female Wistar rats to male Wistar urine induced the appearance of many more Fos-ir cells in all layers of the AOB than exposure to female Wistar urine. As for the mitral/tufted cell layer, the density of Fos-ir cells in the rostral portion (Gi2alpha-positive) of all regions of the AOB was about twice as high as that in the caudal portion when male urine was given. The distribution pattern of Fos-ir cells in response to female urine was not identical to that in response to male urine. That is, the density of Fos-ir cells in the caudal portion was slightly larger than that in the rostral portion in the lateral region, while in other regions the density in the rostral portion was higher than that in the caudal portion. It is likely that information from different pheromones is transmitted to the higher brain regions through the different regions of the AOB.

Thyroid hormone (3,5,3'-triido-L-thyronine) masking/inversion of stimulatory effect of androgen on expression of mk1, a true tissue kallikrein, in the mouse submandibular gland

We studied hormonal regulation of the expression of mkl, a true tissue kallikrein, in the submandibular gland (SMG) of ICR, C3H/ HeN, and F1 (mice from male C3H/HeN x female ICR and in the ones from male ICR x female C3H/HeN). In these mouse strains, mk1 was low in content in males, abundant in females, and increased remarkably by castration of males. In the case of ICR and both F1 mice, injection of 5alpha-dihydrotestosterone (DHT) reduced the mkl level of castrated and female mice. However, the mkl content in female C3H/ HeN mice (or castrated C3H/HeN) was further increased by DHT. To investigate the real action of DHT on mk1 expression, we examined the effects of adrenoectomy/glucocorticoid (dexamethasone, Dex) administration; DHT administration into castrated and adrenoectomized mice; ovariectomy/female hormone (17beta-estradiol, progesterone) administration; and hypophysectomy/combinatory administration of DHT, Dex, and thyroid hormone (3,5,3'-triiodo-L-thyronine, T3) on the mk1 expression in the SMG of ICR mice. Adrenoectomy or ovariectomy did not change the characteristic pattern of mk1 expression in male and female ICR mice. In hypophysectomized (Hypox) ICR male mice, the mk1 content was increased to the same level as in normal ICR females, and DHT administration into the Hypox mice further increased the mk1 level. However, combinatory administration of DHT + T3 or of DHT + T3 + Dex into the Hypox mice lowered the mkl content to the level of normal ICR males, whereas T3 single administration had no effect. Dex single administration into the Hypox mice increased the mkl level to an even higher than that observed with DHT administration. The mk1 level in Hypox mice was not significantly changed by coadministration of Dex with T3. From these results, we conclude that 1) mk1 expression is fundamentally stimulated by androgen (DHT) as are other mk isozymes, such as mk9, mk13, mk22, and mk26 in the mouse SMG, 2) the effect (stimulatory) of DHT on mk1 expression becomes, however, inverted (inhibitory) in the presence of T3. Although the serum T3 level of C3H/HeN female (0.52 ng/ml) was not significantly different from that of C3H/HeN males or ICR mice, coadministration of T3 into C3H/HeN females with a fixed amount of DHT (20 mg/kg body weight) dose dependently repressed the DHT-induced increase in mkl expression, suggesting the lower sensitivity of C3H/HeN females to T3.

Laminar distribution of pheromone-receptive neurons in rat vomeronasal epithelium

1. Responses of vomeronasal sensory neurons to urine excreted from rats, mice and hamsters were studied by the on-cell patch clamp method in slices of sensory epithelium from female Wistar rats. 2. The urine excreted from male and female Wistar rats, male Donryu rats and male C57BL/6 mice induced relatively large responses, while urine from male Sprague-Dawley rats and male Syrian hamsters induced small responses. 3. Of the 62 neurons responding to urine, 57 responded to only one of the urine preparations. 4. The sensory neurons that responded to the male Wistar urine were localized in the apical position of the epithelium where one type of GTP-binding protein, Gi2alpha, is selectively expressed. The neurons in the basal position of the epithelium, which express Goalpha, responded to urine from the other animals. 5. This study demonstrates that sensory neurons responsive to different urinary pheromones are localized in a segregated layer in the rat vomeronasal sensory epithelium.

Differences in androgen-dependent induction of mk1, true tissue kallikrein in C3H/HeN and ICR mouse submandibular gland

Androgen-dependent induction of mk1, true tissue kallikrein, in submandibular gland was studied in C3H/HeN and ICR mice and their F1 progeny. By injection of 5alpha-dihydrotestosterone (DHT), total esteroproteinase activities of female mice were increased to the level of male mice in both C3H/HeN and ICR strains. The mk1 content measured by the radioimmunoassay with anti-mk1 antiserum was decreased in ICR mice, but markedly increased in C3H/HeN mice after DHT injection. We examined the kallikrein isozyme pattern in SMG of two strains using isoelectric focusing. Female ICR mice expressed mainly mk1, mk13 and mk22, and slight mk9. Female C3H/HeN mice expressed mk1, mk9 and pI 6.6-kallikrein. Injection of DHT did not induce any additional kallikrein isozyme in C3H/HeN mice. Furthermore, we made an F1(C3H/HeN) mouse expressing mk13 and mk22 by mating (female C3H/HeN x male ICR). F1(C3H/HeN); these mice showed an androgen response similar to that observed in the ICR mice: mk1 induction in F1(C3H/HeN) mice was decreased by injection of DHT. We suggest the possibility that androgen-dependent mk1 biosynthesis might interact with the expression of other kallikrein isozymes.

Pancreas-sparing duodenectomy: classification, indication and procedures

BACKGROUND/AIMS

Recent advances in the surgical anatomy of the pancreatoduodenal region have permitted duodenum-preserving pancreatic head resection. However, pancreas-sparing duodenectomy (PSD) has not been systematically studied and various types of such procedures have been reported under the designation of PSD.

METHODOLOGY

PSD was performed in 6 patients with extensive duodenal lesions including trauma, mucosa-associated lymphoid tissue (MALT) lymphoma, corrosive necrosis, bleeding, leiomyosarcoma and congenital stenosis. Three patients had the whole papilla Vateri and half of the duodenum preserved and anastomosed to the jejunum. One patient had the duodenal button including the papilla of Vater transplanted to the jejunum. Another patient had the intraduodenal portion of the major papilla excised and the terminal portion of the bile and pancreatic ducts anastomosed to the jejunum.

RESULTS

Two patients with moribund conditions died of the underlying disorders 2 weeks and 3 months after surgery, respectively, but without leakage or other surgery-associated complications. The other 4 patients survived the surgery without anastomotic insufficiency. Three survivors, who had complete preservation of the major and minor papillae along with the half portion of the duodenum, had normal morphology and function of the biliopancreatic system post-operatively. The fourth survivor, that with excision of the intrapancreatic portion of the major papilla, had regurgitation of contrast material into the bile and pancreatic ducts 2 months after surgery on active insufflation of the intestinal lumen, but remained asymptomatic. No abnormality in liver and pancreatic function was detected as of 7 months post-operatively.

CONCLUSIONS

PSD appears to be applicable in the clinical setting, although classification of the procedure seems mandatory in consideration of indications, techniques, and long-term consequences of biliopancreatic function.

Solitary fibrous tumor of the oral cavity: report of a case

A case of benign solitary fibrous tumor of the oral cavity is reported. The tumor occurred in the buccal mucosa of a 34-year-old woman. The surgically removed tumor was 1.5 x 1.2 x 1.0 cm in size and well circumscribed. Histologically, the tumor was composed of spindle-shaped cells that were predominantly arranged haphazardly. Hemangiopericytoma-like areas and collagenous areas were also noted. Immunohistochemically, the tumor cells were positive for CD34 and vimentin. To our knowledge, this is only the second report of solitary fibrous tumor involving the oral cavity.

Flight coverall microclimate evaluation using a Japanese type sweating mannequin

BACKGROUND

It is important to examine the microclimate of a pilot's clothing to evaluate the heat stress the clothing imparts on a pilot, but problems arise with regard to individual variation (phenotype of the pilot, sweating dose, wear condition of the flight coveralls, etc.).

HYPOTHESIS

The present study used a Japanese type sweating mannequin (TOM-III) to evaluate the microclimate of flight coveralls.

METHODS

TOM-III (TOYOBO, Co., Ltd., Tokyo, Japan) has a characteristic Japanese human body type, and the sweat rate and body temperature can be regulated (240 g of sweat per hour, 36.0 degrees C). The microclimate of the clothing was evaluated by means of 20 temperature/humidity sensors located on the surface of the mannequin skin. TOM-III wore four different assemblies of clothing (CWU-66/P USAF chemical defense flight coverall; JASDF summer-type flight coverall which is similar to the nonchemical defense USAF flight coverall; ordinary 100% cotton underwear; and CWU-66/ P with cotton underwear). We put TOM-III in climatic chamber (21.2 +/- 0.5 degrees C, 50.0 +/- 3.0% relative humidity (RH), 0.1 m air flow x s(-1), dressed in test clothing, and measured the inside temperature (IT) and inside relative humidity (IRH) of the clothing for 60 min (10 min non-sweating, 30 min sweating and 20 min non-sweating).

RESULTS

Approximately 5 min after the onset of sweating, the IRH of the CWU-66/P (38.0%) was lower than JASDF flight coverall (42.1%; p < 0.01). At the end of the sweating period, the IRH of the CWU-66/P and the JASDF flight coverall were 46.2% and 52.6%, respectively (p < 0.01). The results indicated that the CWU-66/P flight coverall was better suited for heat stress than the JASDF summer-type flight coverall.

CONCLUSIONS

TOM-III may be useful for microclimate evaluation and/or the development of clothing without considering individual variation against various climatic conditions.

[Polymyalgia rheumatica and myelitis associated with anti-cardiolipin antibody]

A 78-year-old woman was admitted to our hospital on September 14, 1992, because of systemic myalgia and stiffness, joint pain, and gait disturbance. She had begun to feel headache and pain in the neck and shoulder in the middle of August, 1992. The pain became systemic, and was accompanied by a low-grade fever, which was unresponsive to NSAIDs. On admission, she had no joint swelling or deformities in the extremities. Neurological examination revealed weakness in the right leg, hypoalgesia below the left C4 level, hyperreflexia in the right extremities, and right Babinski's sign. The erythrocyte sedimentation rate was very high (100 mm/h). Levels of other acute phase reactants were also high. Tests for antinuclear antibody and anti-cardiolipin antibody were positive, but a test for rheumatoid factor was negative. Creatine kinase activity was within normal limits. A T1-weighted magnetic resonance image of the cervical spine at 0.5 T showed an intramedullary low signal. A T2-weighted image showed a borderless spindle-like high signal. Four nodules enhanced by Gd DTPA were seen at C1-C4. The age at onset, myalgia, stiffness, and erythrocyte sedimentation rate were considered to be consistent with a diagnosis of polymyalgia rheumatica. Glucocorticoid treatment was therefore started, and a dramatic clinical improvement was evident within a few days. The patient was discharged from hospital on November 30, 1992. To our knowledge, myelopathy complicated by polymyalgia rheumatica has never been reported previously. Recently, some patients with polymyalgia rheumatica have been reported to have anti-cardiolipin antibody in serum. In the present case anti-cardiolipin antibody may have played a role in the formation of microemboli or in angitis of the cervical spine.

Introductory remarks on umami taste

Psychophysical and electrophysiological studies indicated that the umami substances have no enhancing activity on other primary tastes. Experiments using amiloride clearly show that the umami component of canine chorda tympani nerve response to umami substances is independent of the salt component. Single fiber analysis of the responses of the mouse glossopharyngeal nerve and the monkey primary taste cortex neuron show that the responses to umami substances are independent of other primary tastes. A large synergism between monosodium glutamate (MSG) and disodium 5'-inosinate (IMP) or disodium 5'-guanylate (GMP) is observed in dogs and is explained in terms of allosteric effect. The order of intensity of umami taste induced by a mixture of 0.5 mM GMP and 1.5 mM of various agonists for the glutamate receptors was glutamate > ibotenate > DL(+)-2-amino-4-phosphonobutyric acid (DL-AP4)-(+)-1- aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD). Kainate, N-methyl-D-aspartate (NMDA) and (RS)--amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), which are agonists for ionotropic receptors, have no umami taste. It was concluded that the umami receptor is not identical to any of known glutamate receptors, and there seems to be a unique receptor for umami.