Olfactory receptors (ORs) comprise the largest super-family of rhodopsin-like G-protein coupled receptors (GPCR) that involve the recognition and discrimination of thousands of odorants. We recently succeeded in functional reconstitution of mouse ORs in mammalian cell lines and provided molecular evidence that structurally-related ORs recognized overlapping sets of odorants with distinct ligand specificities. Here we show that mOR-EG, a mouse olfactory receptor that was isolated from a eugenol-responsive cell, recognizes 22 different odorants with EC50values ranging from a few µM to several hundred µM. We constructed a molecular model of mOR-EG using the recent atomic-level structure of bovine rhodopsin. Site-directed mutations were introduced in a potential ligand-binding pocket based on computational ligand-docking simulation. Mutations of some amino acid residues in TM3, TM5, and TM6 dramatically affected the EC50value of eugenol in Ca2+ imaging. Finally, we succeeded in rational receptor design with predicted ligand specificity by introducing point mutations in the binding site, confirming the accuracy of the binding site mapping. The current studies also help understand mechanisms underlying molecular recognition by GPCRs, with implications for therapeutic application.

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Gustatory and anticipatory cephalic stimuli that are detected during a meal yield nutritional information and aid in the efficient digestion of food. It is possible that animals can detect the amount of dietary food and its quality via cephalic relay to initiate proper digestion in the alimentary tract. The abdominal vagus conveys primary afferent nutritional information from the digestive system to the brain and modulates gastrointestinal motor and secretory activity that ensures the food digestion through local and central reflexes. Almost all the 5-HT in the body exists in the enterochromaffin (EC) cells in the alimentary tract, but the physiological significance of the mucosal 5-HT is not well elucidated. In the present paper, we reviewed recent advances in studies on gut nutrient perception and proposed the hypothesis that 5-HT derived from EC cells acts as a general transmitter of gut nutrient sensing by the abdominal vagus.

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We feel a wide range of temperatures spanning from cold to heat. Within this range, temperatures over about 43°C and below about 15°C evoke not only a thermal sensation, but also a feeling of pain. In mammals, six thermosensitive ion channels have been reported, all of which belong to the TRP (transient receptor potential) super family. These include TRPV1 (VR1), TRPV2 (VRL-1), TRPV3, TRPV4, TRPM8 (CMR1), and TRPA1 (ANKTM1). These channels exhibit distinct thermal activation thresholds (>43°C for TRPV1, >52°C for TRPV2, >32-39°C for TRPV3, >27-35°C for TRPV4, <25-28°C for TRPM8, and <17°C for TRPA1) and are expressed in primary sensory neurons as well as other tissues. The involvement of TRPV1 in thermal nociception has been demonstrated by multiple methods, including the analysis of TRPV1-deficient mice. Temperature thresholds for activation of TRPV1, TRPV4, and TRPM8 are not fixed but changeable. Reduction of the temperature threshold for TRPV1 activation is thought to be one mechanism of inflammatory pain. Significant advances in thermosensation research have been made in the last several years with the cloning and characterization of thermosensitive TRP channels. With these clones in hand, we can begin to understand thermosensation from a molecular standpoint.

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We reported that activation of P2X2/3 heteromeric channels in Aδ-DRG neurons causes tactile allodynia and activation of P2X3 in C-fiber causes nocifensive behavior. We also found that tactile allodynia under the chronic pain state requires an activation of P2X4 ionotropic ATP receptor and p38 mitogen-activated protein kinase in spinal microglia.

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G protein-coupled receptors (GPCRs) are the most famous target proteins for medicinal drugs. So far, heterogeneity of GPCRs is mainly focused on genetic variation. However, it has been reported that the structure and function of GPCRs are modified by several mechanisms after translation. RNA editing introduces the amino acid different from that encoded in genome by changing the nucleotide. Dimer formation is another example of how heterogeneity is produced. Many receptors form homo- or hetero-dimers, and obtain different function from original receptors. Receptors are regulated by several means to modulate stimulation strength. Receptor subtype is often differentially regulated by receptor kinases and/or second messenger-regulated kinases. There is a new type of receptor that shows a novel structural feature, a long amino terminal region belonging to class B seven transmembrane receptors. The physiological function of this class of receptor is assumed to play a role in cell-cell communication. This novel structural feature may directly link GPCR to the cytoskeleton. These mechanisms to produce functional and structural heterogeneity may explain how cells evoke different responses in different tissues or cells upon the same stimulation. Thus, the post-translational mechanism to produce heterogeneity provides additional flexibility when cells respond to one extracellular stimulus.

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Mitiglinide calcium hydrate (mitiglinide, Glufast^®) is a new insulinotropic agent of the glinide class with rapid onset. Mitiglinide is thought to stimulate insulin secretion by closing the ATP-sensitive K⁺ (K_ATP) channels in pancreatic β-cells, and its early insulin release and short duration of action would be effective in improving postprandial hyperglycemia. In studies of various cloned K_ATP channels, mitiglinide shows a higher selectivity for the β-cell type of SUR1/Kir6.2 than the cardiac and smooth muscle types of K_ATP channels in comparison with glibenclamide and glimepiride. In vitro and in vivo studies demonstrated the insulinotropic effect of mitiglinide is more potent than that of nateglinide, and mitiglinide surpassed in controlling postprandial hyperglycemia in normal and diabetic animals. In clinical trials, treatment with mitiglinide provided lasting improvement of postprandial hyperglycemia in Type 2 diabetic patients and decreased the fasting plasma glucose levels and HbA_1C values. The incidence of adverse events related to mitiglinide were nearly equivalent to placebo; in particular there was no difference with the frequency of hypoglycemia. The results from these studies indicated that mitiglinide could be expected to possess good therapeutic features of being effective in reducing postprandial glucose excursions in the early stage of Type 2 diabetes and less incidence of events suggestive of hypoglycemia.

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Olmesartan medoxomil is a new angiotensin II receptor blocker (ARB) indicated for the treatment of hypertension. Olmesartan medoxomil is a pro-drug that is converted to the active metabolite olmesartan. Olmesartan does not undergo further metabolism and does not interact with cytochrome P450 enzymes. Olmesartan is a potent ARB with high selectivity for the type 1 (AT₁) receptor subtype and shows insurmountable antagonism against the AT₁ receptor in vascular tissues. This antagonistic mode, which could be attributed to tight binding of this drug to the receptor, would underlie the potent and persistent action of olmesartan medoxomil in vivo. In fact, oral administration of olmesartan medoxomil produces a potent and long-lasting antihypertensive action without inducing tachycardia. The preventive effects of olmesartan medoxomil on end-organ damage in the kidney, heart, and blood vessels have been demonstrated in various animal models. In clinical studies, olmesartan medoxomil is shown to be well tolerated and have an excellent safety profile that is comparable to that of placebo. Head-to-head comparisons with other ARBs (losartan, valsartan, irbesartan, and candesartan cilexetil) conducted in the United States and Europe have revealed that olmesartan medoxomil is superior to these other ARBs in lowering blood pressure. These facts suggest that olmesartan medoxomil would be beneficial for the treatment of hypertension and other end-organ diseases.

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Pseudolarix amabilis Rehd. extract was examined in vitro for antibacterial effects, anti-inflammatory effects, and inhibitory effects on histamine release. Pseudolarix amabilis Rehd. extract was also examined for efficacy on dermatitis in atopic dermatitis model mice (NC mice) and effects on keratinous moisture level and transepidermal water loss in miniature pigs. Pseudolarix amabilis Rehd. extract had antibacterial effects on Staphylococcus aureus, Candida albicans, and Streptococcus pyogenes; however this antibacterial effect varied with the temperature at which and conditions under which Pseudolarix amabilis Rehd. was extracted. Pseudolarix amabilis Rehd. extract at the final concentration of 2 mg/mL significantly inhibited the hyaluronidase activity; and at 0.005, 0.05, and 0.5 mg/mL, it also significantly inhibited the histamine release. In the mice in which atopic dermatitis had been induced, 28-day administration of Pseudolarix amabilis Rehd. extract at 4 and 400 mg/mL significantly inhibited aggravation of dermatitis without having effects on body weight. In the dorsal skin of miniature pigs, Pseudolarix amabilis Rehd. extract at 4 and 400 mg/mL significantly increased keratinous moisture level with the increase in the number of dosing days, and caused no changes in transepidermal water loss. From the above results, it is clear that Pseudolarix amabilis Rehd. extract inhibits both proliferation of bacteria and inflammation caused by antigens. Furthermore, it is suggested that Pseudolarix amabilis Rehd. extract will serve as a medicinal drug which effectively moistens the skin and prevents and heals dermatitis.

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