The existence of a discrete 'link' peptide in epithelial mucins has been debated for many years. There is evidence that at least some mucins contain a specific 'link' peptide (or glycopeptide) that enhances mucin polymerization by forming disulphide bridges to large mucin glycoprotein subunits. A major difficulty has been to know whether the reported differences in putative 'link' components represent artifacts generated by inter-laboratory differences in technical procedures used in mucin purification. The present paper outlines the results of a collaborative study involving five laboratories and 53 samples of purified gastrointestinal mucins (including salivary, gastric, small-intestinal and colonic mucins) prepared by five techniques from four different animal species. An early step in mucin purification in all cases was the addition of proteinase inhibitors. Representative mucins were analysed for their composition, electrophoretic mobility in SDS/polyacrylamide-gel electrophoresis before and after disulphide-bond reduction, and for their reactivity with monospecific antibodies developed against the 118 kDa putative 'link' glycopeptide isolated from either rat or human small-intestinal mucins. Our results indicate that, despite differences in laboratory techniques, preparative procedures, organs and species, each of the purified mucins contained a 'link' component that was released by disulphide-bond reduction and produced a band on SDS/polyacrylamide-gel electrophoresis at a position of approx. 118 kDa. After electroelution and analyses, the 118 kDa bands from the different mucins were found to have similar amino acid profiles and to contain carbohydrate. It would appear therefore that a 'link' glycopeptide of molecular mass approx. 118 kDa is common to all of the gastrointestinal mucins studied.
Rehabilitation of eating and swallowing functions from the viewpoint of quality of life should attempt to restore not only the physical, but also sensory function. As the size and shape of the intra-oral bolus of food provides oral sensory information important for eating and swallowing, we investigated the stereognostic ability of the tongue in 269 young adults (mean age: 24.5 years) and 60 seniors (mean age: 80.5 years); all of whom had no eating or swallowing complaints. Assessment of the stereognostic ability involved identifying 20 differently shaped test pieces placed in the oral cavity. The young adults identified a significantly higher number of differently shaped test pieces than the seniors (mean correct number of responses: 16.5 and 10.1 respectively; P < 0.001). Gender and the presence of palatal covers did not have any significant effect on stereognostic ability. The test pieces were categorized into six groups based on the shape. When the young adults misidentified a piece, they often selected another piece within the same group, almost never selecting a piece from another group. The seniors, however, chose test pieces from different groups. Moreover, to determine whether stereognosis could be improved through training, we conducted training involving four senior subjects in their 80s, who correctly identified 10 or fewer pieces. After the training, the number of correct answers increased significantly (P < 0.05). These findings indicate that seniors show decreased stereognostic ability of the tongue compared with young adults and suggest the possibility of recovering the ability using our training method.
Nitrite-induced transformation of 3-amino-4-monomethylamino-2',7'-difluorofluorecein (DAF-FM) to the triazol form (DAF-FMT) was studied using bacterial fraction of mixed whole saliva. The transformation at pH 7 was inhibited by SCN(-), suggesting that nitrosative stresses were small in the oral cavity at the pH value as SCN(-) was a normal component of saliva. DAF-FMT formation was much faster at pH 5.2 than 7 and ONSCN generated by the reaction of HNO(2) with SCN(-) mainly contributed to its formation at pH 5.2. Coffee and phenolic antioxidants inhibited the DAF-FMT formation less effectively at pH 5.2 than pH 7. The less effectiveness was discussed to be due to slow scavenging of ONSCN, which contributed mainly to the formation of DAF-FMT at pH 5.2, by coffee and phenolics. Since nitrite-induced formation of ONSCN should become faster as the pH decreases, it was suggested that nitrosative stresses to oral tissues became serious under acidic conditions.
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