Action of Protein Tyrosine Kinase Inhibitors on the Hypotonicity-Stimulated Trafficking Kinetics of Epithelial Na+ Channels (ENaC) in Renal Epithelial Cells: Analysis Using a Mathematical Model

Background/Aims: Epithelial Na+ channels (ENaCs) play crucial roles in control of blood pressure by determining the total amount of renal Na+ reabsorption, which is regulated by various factors such as aldosterone, vasopressin, insulin and osmolality. The intracellular trafficking process of ENaCs regulates the amount of the ENaC-mediated Na+ reabsorption in the collecting duct of the kidney mainly by determining the number of ENaC expressed at the apical membrane of epithelial cells. Although we previously reported protein tyrosine kinases (PTKs) contributed to the ENaC-mediated epithelial Na+ reabsorption, we have no information on the role of PTKs in the intracellular ENaC trafficking. Methods: Using the mathematical model recently established in our laboratory, we studied the effect of PTKs inhibitors (PTKIs), AG1296 (10 µM: an inhibitor of the PDGF receptor (PDGFR)) and AG1478 (10 µM: an inhibitor of the EGF receptor (EGFR)) on the rates of the intracellular ENaC trafficking in renal epithelial A6 cells endogenously expressing ENaCs. Results: We found that application of PTKIs significantly reduced the insertion rate of ENaC to the apical membrane by 56%, the recycling rate of ENaC by 83%, the cumulative time of an individual ENaC staying in the apical membrane by 27%, the whole life-time after the first insertion of ENaC by 47%, and the cumulative Na+ absorption by 61%, while the degradation rate was increased to 3.8-fold by application of PTKIs. These observations indicate that PTKs contribute to the processes of insertion, recycling and degradation of ENaC in the intracellular trafficking process under a hypotonic condition. Conclusion: The present study indicates that application of EGFR and PDGFR-inhibitable PTKIs reduced the insertion rate (kI), and the recycling rate (kR) of ENaCs, but increased degradation rate (kD) in renal A6 epithelial cells under a hypotonic condition. These observations indicate that hypotonicity increases the surface expression of ENaCs by increasing the insertion rate (kI) and the recycling rate (kR) of ENaCs associated with a decrease in the degradation rate but without any significant effects on the endocytotic rate (kE) in EGFR and PDGFR-related PTKs-mediated pathways

Improvement of Diabetes Mellitus Symptoms by Intake of Ninjin'yoeito

Diabetes mellitus is a well-known common disease and one of the most serious social problems in the worldwide. Although various types of drugs are developed, the number of patients suffering from diabetes mellitus is still increasing. Ninjin'yoeito (NYT) is one of formulas used in Japanese traditional herbal medicines for improving various types of metabolic disorders. However, the effect of NYT on diabetes mellitus has not yet been investigated. In the present study, we tried to clarify the action of NYT on the serum glucose level in streptozotocin (STZ)-induced diabetic mice. We found that intake of NYT decreased the serum glucose level and increased insulin sensitivity in STZ-induced diabetic mice. NYT treatment also improved acidification of the interstitial fluid around skeletal muscles found in STZ-induced diabetic mice, while the interstitial fluid acidification has been reported to cause insulin resistance. Furthermore, in the proximal colon of STZ-induced diabetic mice, NYT treatment showed a tendency to increase the expression of sodium-coupled monocarboxylate transporter 1 (SMCT1), which has ability to absorb weak organic acids (pH buffer molecules) resulting in improvement of the interstitial fluid acidification. Based on these observations, the present study suggests that NYT is a useful formula to improve hyperglycemia and insulin resistance via elevation of interstitial fluid pH in diabetes mellitus, which might be caused by increased absorption of pH buffer molecules (SMCT1 substrates, weak organic acids) mediated through possibly elevated SMCT1 expression in the proximal colon

Lymphoepithelial Carcinoma in the Lateral Tongue: The Case Report

Lymphoepithelial carcinoma (LEC) of the tongue is a rare subtype of squamous cell carcinoma. Histologically, it is an undifferentiated carcinoma with rich lymphocyte and plasma cell infiltration. The most common location for LEC in the head and neck is the salivary glands, and LEC of the oral cavity is extremely rare. The second case report of LEC in the lateral tongue is presented. In addition, a review of the literature was performed, and the relationship between LEC and Epstein-Barr virus infection was considered

The Diagnostic Capacity of Pre-treatment 18F-FDG PET/CT for Predicting the Extranodular Spread of Lymph Node Metastases in Patients with Oral Squamous Cell Carcinoma

The aim of this study was to evaluate the ability of pretreatment 90-min 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) to predict the extranodular spread of lymph node metastases in oral squamous cell carcinoma. We retrospectively reviewed the cases of 56 patients who underwent pretreatment 18F-FDG PET/CT and surgery with neck dissection. Maximum standardized uptake value, metabolic tumor volume, and total lesion glycolysis were measured for the 56 primary sites and maximum standardized uptake value was measured for 115 lymph node levels. Extranodular spread was present at 9 lymph node levels in 7 patients. Significant differences were found in metabolic tumor volume and total lesion glycolysis of the primary site, and in lymph node maximum standardized uptake value, between patients with and without extranodular spread (p<0.05). Combining primary site total lesion glycolysis and lymph node maximum standardized uptake volume at their respective optimal cutoffs, the sensitivity, specificity, and accuracy for predicting extranodular spread were 89%, 92%, and 92%, respectively. Pretreatment 18F-FDG PET/CT is useful for predicting extranodular spread in patients with oral squamous cell carcinoma. The combined use of primary site total lesion glycolysis and lymph node maximum standardized uptake value showed greater predictive value than either predictor singly

Clinical Significance of Cytoplasmic IgE-Positive Mast Cells in Eosinophilic Chronic Rhinosinusitis

Cross-linking of antigen-specific IgE bound to the high-affinity IgE receptor (Fc epsilon RI) on the surface of mast cells with multivalent antigens results in the release of mediators and development of type 2 inflammation. Fc epsilon RI expression and IgE synthesis are, therefore, critical for type 2 inflammatory disease development. In an attempt to clarify the relationship between eosinophilic chronic rhinosinusitis (ECRS) and mast cell infiltration, we analyzed mast cell infiltration at lesion sites and determined its clinical significance. Mast cells are positive for c-kit, and IgE in uncinated tissues (UT) and nasal polyps (NP) were examined by immunohistochemistry. The number of positive cells and clinicopathological factors were analyzed. Patients with ECRS exhibited high levels of total IgE serum levels and elevated peripheral blood eosinophil ratios. As a result, the number of mast cells with membranes positive for c-kit and IgE increased significantly in lesions forming NP. Therefore, we classified IgE-positive mast cells into two groups: membrane IgE-positive cells and cytoplasmic IgE-positive cells. The amount of membrane IgE-positive mast cells was significantly increased in moderate ECRS. A positive correlation was found between the membrane IgE-positive cells and the radiological severity score, the ratio of eosinophils, and the total serum IgE level. The number of cytoplasmic IgE-positive mast cells was significantly increased in moderate and severe ECRS. A positive correlation was observed between the cytoplasmic IgE-positive cells and the radiological severity score, the ratio of eosinophils in the blood, and the total IgE level. These results suggest that the process of mast cell internalization of antigens via the IgE receptor is involved in ECRS pathogenesis

Regulation of the Epithelial Na + Channel by Cytosolic ATP

The epithelial Na+ channel (ENaC), composed of three subunits (alphabetagamma), is expressed in various Na(+)-absorbing epithelia and plays a critical role in salt and water balance and in the regulation of blood pressure. By using patch clamp techniques, we have examined the effect of cytosolic ATP on the activity of the rat alphabetagammaENaC (rENaC) stably expressed in NIH-3T3 cells and in Madin-Darby canine kidney epithelial cells. The inward whole-cell current attributable to rENaC activity ran down when these cells were dialyzed with an ATP-free pipette solution in the conventional whole-cell voltage-clamping technique. This run down was prevented by 2 mM ATP (but not by AMP or ADP) in the pipette solution or by the poorly or non-hydrolyzable analogues of ATP (adenosine 5'-O-(thiotriphosphate) and adenosine 5'-(beta,gamma-imino)triphosphate) in both cell lines, suggesting that protection from run down was mediated through non-hydrolytic nucleotide binding. Accordingly, we demonstrate binding of ATP (but not AMP) to alpharENaC expressed in Madin-Darby canine kidney cells, which was inhibited upon mutation of the two putative nucleotide-binding motifs of alpharENaC. Single channel analyses indicated that the run down of currents observed in the whole-cell recording was attributable to run down of channel activity, defined as NPo (the product of the number of channels and open probability). We propose that this novel ATP regulation of ENaC may be, at least in part, involved in the fine-tuning of ENaC activity under physiologic and pathophysiologic conditions

Regulation of Epithelial Sodium Transport via Epithelial Na+ Channel

Renal epithelial Na+ transport plays an important role in homeostasis of our body fluid content and blood pressure. Further, the Na+ transport in alveolar epithelial cells essentially controls the amount of alveolar fluid that should be kept at an appropriate level for normal gas exchange. The epithelial Na+ transport is generally mediated through two steps: (1) the entry step of Na+ via epithelial Na+ channel (ENaC) at the apical membrane and (2) the extrusion step of Na+ via the Na+, K+-ATPase at the basolateral membrane. In general, the Na+ entry via ENaC is the rate-limiting step. Therefore, the regulation of ENaC plays an essential role in control of blood pressure and normal gas exchange. In this paper, we discuss two major factors in ENaC regulation: (1) activity of individual ENaC and (2) number of ENaC located at the apical membrane

The algal polysaccharide ulvan suppresses growth of hepatoma cells

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