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

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

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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CALHM3 Is Essential for Rapid Ion Channel-Mediated Purinergic Neurotransmission of GPCR-Mediated Tastes

Binding of sweet, umami, and bitter tastants to G protein-coupled receptors (GPCRs) in apical membranes of type II taste bud cells (TBCs) triggers action potentials that activate a voltage-gated nonselective ion channel to release ATP to gustatory nerves mediating taste perception. Although calcium homeostasis modulator 1 (CALHM1) is necessary for ATP release, the molecular identification of the channel complex that provides the conductive ATP-release mechanism suitable for action potential-dependent neurotransmission remains to be determined. Here we show that CALHM3 interacts with CALHM1 as a pore-forming subunit in a CALHM1/CALHM3 hexameric channel, endowing it with fast voltage-activated gating identical to that of the ATP-release channel in vivo. Calhm3 is co-expressed with Calhm1 exclusively in type II TBCs, and its genetic deletion abolishes taste-evoked ATP release from taste buds and GPCR-mediated taste perception. Thus, CALHM3, together with CALHM1, is essential to form the fast voltage-gated ATP-release channel in type II TBCs required for GPCR-mediated tastes. Ma et al. identify a CALHM1/CALHM3 hetero-hexameric ion channel as the mechanism by which type II taste bud cells release ATP as a neurotransmitter to gustatory neurons in response to GPCR-mediated tastes, including sweet, bitter, and umami substances. © 2018 Elsevier Inc

Food Frontiers : An academically sponsored new journal

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Interactive Actions of Aldosterone and Insulin on Epithelial Na+ Channel Trafficking

Epithelial Na+ channel (ENaC) participates in renal epithelial Na+ reabsorption, controlling blood pressure. Aldosterone and insulin elevate blood pressure by increasing the ENaC-mediated Na+ reabsorption. However, little information is available on the interactive action of aldosterone and insulin on the ENaC-mediated Na+ reabsorption. In the present study, we tried to clarify if insulin would modify the aldosterone action on the ENaC-mediated Na+ reabsorption from a viewpoint of intracellular ENaC trafficking. We measured the ENaC-mediated Na+ transport as short-circuit currents using a four-state mathematical ENaC trafficking model in renal A6 epithelial cells with or without aldosterone treatment under the insulin-stimulated and -unstimulated conditions. We found that: (A) under the insulin-stimulated condition, aldosterone treatment (1 µM for 20 h) significantly elevated the ENaC insertion rate to the apical membrane ( k I ) 3.3-fold and the ENaC recycling rate ( k R ) 2.0-fold, but diminished the ENaC degradation rate ( k D ) 0.7-fold without any significant effect on the ENaC endocytotic rate ( k E ); (B) under the insulin-unstimulated condition, aldosterone treatment decreased k E 0.5-fold and increased k R 1.4-fold, without any significant effect on k I or k D . Thus, the present study indicates that: (1) insulin masks the well-known inhibitory action of aldosterone on the ENaC endocytotic rate; (2) insulin induces a stimulatory action of aldosterone on ENaC apical insertion and an inhibitory action of aldosterone on ENaC degradation; (3) insulin enhances the aldosterone action on ENaC recycling; (4) insulin has a more effective action on diminution of ENaC endocytosis than aldosterone