The MaxiK channel is the large-conductance, voltage-dependent, and Ca2+-activated K+ channel. This channel is almost ubiquitously distributed among mammalian tissues including smooth muscles. The ability of MaxiK to work as a rheostat fine tuning membrane potential and intracellular Ca2+ enables it to mediate opposite functions: it facilitates contraction, but also acts as a negative feedback mechanism to restore tone after a contraction cycle. MaxiK activation mediates relaxations to a variety of physiological substances, whereas its inhibition plays a significant role in contractile responses. At the molecular level, MaxiK is a protein complex formed by at least two integral dissimilar membrane subunits, the pore-forming α-subunit and a regulatory β-subunit. In smooth muscles, β1 is the predominant subunit and most MaxiK seem to be assembled of α- and β1-subunits. The presence of the β1-subunit confers MaxiK with higher Ca2+/voltage sensitivity, which makes this channel an efficient tuner of smooth muscle functions in physiological conditions. The enhanced smooth muscle mechanical activities in mice lacking the β1-subunit gene support the principal role of this channel molecular component in tissue and whole animal functions. In this review, we discuss MaxiK channel roles as a tuner of smooth muscle contractility, especially focusing attention on the modulatory β1-subunit.
Increasing use of tobacco and its related health problems are a great concern in the world. Recent epidemiological findings have demonstrated the positive association between cigarette smoking and several gastrointestinal (GI) diseases, including peptic ulcer and cancers. Interestingly, smoking also modifies the disease course of ulcerative colitis (UC). Nicotine, a major component of cigarette smoke, seems to mediate some of the actions of cigarette smoking on the pathogenesis of GI disorders. Nicotine worsens the detrimental effects of aggressive factors and attenuates the protective actions of defensive factors in the processes of development and repair of gastric ulceration. Nicotine also takes part in the initiation and promotion of carcinogenesis in the GI tract. In this regard, nicotine and its metabolites are found to be mutagenic and have the ability to modulate cell proliferation, apoptosis, and angiogenesis during tumoriogenesis through specific receptors and signalling pathways. However, to elucidate this complex pathogenic mechanism, further study at the molecular level is warranted. In contrast, findings of clinical trials give promising results on the use of nicotine as an adjuvant therapy for UC. The beneficial effect of nicotine on UC seems to be mediated through multiple mechanisms. More clinical studies are needed to establish the therapeutic value of nicotine in this disease.
Chung-Yeul-Gue-Soup-Sa-Gan-Tang (CYT), a traditional Korea herbal medicine, has been widely used in Korea for the treatment of various immunological disorders, including allergic asthma. In this study, CYT was examined in vitro and tested for possible immunological effects. The results demonstrated that CYT had no mitogenic effects on unstimulated CD4+ T cells, but rather increased CD4+ T cell proliferation upon activation with anti-CD3/CD28 antibody. Under the Th0 condition, CYT also enhanced expression of interleukin (IL)-2 in purified murine CD4+ T cells assayed by real-time PCR, suggesting that CYT moderately increases the activity of helper T cells upon T cell receptor ligation under the neutral condition. However, the Th1 cells were overpopulated following CYT treatment under the Th1 condition, while Th2 cells were under-populated in the Th2 driven condition. In addition, under Th1/Th2-skewed conditions, the levels of IL-4 were considerably decreased, while the expression of T-bet and interferon-γ were increased with CYT treatment. Thus, CYT enhances Th1 lineage development from naive CD4+ T cells both by increasing Th1 specific cytokine secretion and repressing Th2 specific cytokine production. These results suggest that CYT is a desirable agent for the correction of Th2 dominant pathological disorders.
Characterization of the γ-aminobutyric acid (GABA)B receptor involved in the motility of dog small intestine was analyzed by application of the microdialysis method to the small intestine of the whole body of the dog. The reverse transcription-polymerase chain reaction (RT-PCR) was used. Intraarterial administration of muscimol induced acceleration of motility associated with acetylcholine (ACh) release, these responses being antagonized by bicuculline. Intraarterial administration of baclofen induced inhibition of motility associated with ACh release, these responses being antagonized by CGP62349. GABA induced inhibition of motility associated with decrease in ACh release. CGP62349 alone induced acceleration of motility associated with increase in ACh release. RT-PCR revealed the presence of mRNAs for both subunits of GABAB receptor, GABAB1 and GABAB2, in the dog small intestine, although GABAB1 subunits were 6 isoforms of GABAB1 (GABAB1(a) – GABAB1(g)), except GABAB1(d). Thus, the GABAB receptor located at cholinergic neurons as a heterodimer with subunits of GABAB1 and GABAB2 in the dog small intestine operates predominantly relative to the GABAA receptor in physiological motility.
Urotensin II induced sustained contraction with an EC50 value of 2.29 ± 0.12 nM in rat aorta. Urotensin II (100 nM) transiently increased cytosolic Ca2+ level ([Ca2+]i), followed by a small sustained phase superimposed with rhythmic oscillatory change. In the presence of verapamil and La3+, the [Ca2+]i oscillation was completely inhibited, although a small transient increase in [Ca2+]i remained. The urotensin II-induced contraction was also partially inhibited by verapamil and La3+. Combined application of verapamil, La3+, and thapsigargin completely inhibited the increase in [Ca2+]i with only partial inhibition of the contraction elicited by urotensin II. Urotensin II increased myosin light chain (MLC) phosphorylation to a level greater than that induced by 72.7 mM KCl (high K+). Pretreatment with Go6983 (PKC inhibitor), U0126 (MEK inhibitor), or SB203580 (p38MARK inhibitor) partially inhibited the urotensin II-induced contraction with no effects on the high K+-induced contractions. Wortmannin (MLC kinase inhibitor) only partially inhibited urotensin II-induced contraction, although it completely inhibited the high K+-induced contraction. These results suggest that urotensin II-induced contraction is mediated by the Ca2+/calmodulin/MLC kinase system and modulated by the Ca2+ sensitization mechanisms to increase MLC phosphorylation. In addition, activations of PKC, p38MAPK, and ERK1/2 modulate the contractility mediated by urotensin II in rat aorta.
The aim of this work was to verify whether formalin would induce leukocyte recruitment following intraperitoneal (i.p.) injection in rats. Formalin (1.25 – 2.5%) induced cell recruitment, which was concentration- and time-dependent (0 – 24 h). Two peaks of leukocyte recruitment were observed. The first peak (from 2 to 4 h) was characterized by a mixed polymorphonuclear and lymphocyte cell population (representing an increase of 100 – 220% and 55 – 60%, respectively), whereas the second peak was characterized by a marked increase in lymphocytes at 24 h (representing an increase of 230%). Pretreatment of animals with specific antagonists for neurokinin NK1, NK2, and NK3 receptors (SR140333, SR48968, and SR142801 compounds, respectively) reduced the early leukocyte increase (representing a significant reduction of 65%, 51%, and 46%, respectively), whereas only the treatment with NK2-specific antagonist reduced the late cell increase induced by formalin injection (amounting to a significant reduction of 48%). These results suggested that substance P, neurokinin A, and neurokinin B release accounted for formalin-induced cell migratory activity. The anti-inflammatory drug dexamethasone also reduced cell recruitment, which was mainly related to a reduction in 79% of the neutrophils at 4 h following 1.25% formalin injection, suggesting also a release of lipid mediators (eicosanoids and/or platelet-activating factor) and/or cytokines/chemokines by the formalin injection.
In the present experiment, we studied the action of buckwheat polyphenol (BWP, from Fagopyrum esculentum MOENCH) in a repeated cerebral ischemia model, which induced a strong and long-lasting impairment of spatial memory in 8-arm radial maze with hippocampal CA1 cell death in rats. BWP (600 mg/kg, continuous 21-day p.o.) significantly ameliorated not only the impairment of spatial memory in the 8-arm radial maze, but also necrosis and TUNEL-positive cells in the hippocampal CA1 area subjected to repeated cerebral ischemia (10 min × 2 times occlusion, 1-h interval) in rats. In order to investigate the mechanism of BWP protective action, we measured the release of glutamate and NOx− (NO2− + NO3−) production induced by repeated cerebral ischemia in the rat dorsal hippocampus using microdialysis. A 14-day BWP treatment significantly inhibited the excess release of glutamate after the second occlusion. In addition, the BWP remarkably suppressed a delayed increase in NOx− (NO2− + NO3−) induced by repeated cerebral ischemia in the dorsal hippocampus as determined in vivo by microdialysis. However, the 14-day treatment did not affect hippocampal blood flow in either intact rats or rats subjected to repeated ischemia measured by lasser Doppler flowmeter. These results suggested that BWP might ameliorate spatial memory impairment by inhibiting glutamate release and the delayed generation of NOx− in rats subjected to repeated cerebral ischemia.
MMP-9 or Gelatinase B, a member of the matrix metalloproteinase family (MMPs), plays important roles in physiological events such as tissue remodeling and in pathological processes that lead to destructive bone diseases, including osteoarthritis and periodontitis. In addition to its effect on the increase of total bone mass, statin (an HMG-CoA reductase inhibitor) suppresses the expression of MMPs. In this study, we proposed that simvastatin reduces MMP-9 expression in osteoblasts and HT1080 fibrosarcoma cell line. Gelatin zymography, Western blot analysis and reverse transcriptase-PCR were used to investigate the effects of simvastatin on MMP-9 in primary calvaria cells, U2-OS osteosarcoma cells, and HT1080 fibrosarcoma cells. The results from gelatin zymography and Western blot analysis revealed that simvastatin suppressed MMP-9 activity in these cells in concentration- and time-dependent manners. The effective concentrations of simvastatin were 100 – 500 nM, 5 – 15 μM, and 2.5 – 10 μM in primary calvaria, U2-OS, and HT1080 cells, respectively. Collectively, these results suggest that simvastatin is a potent drug for inhibition of MMP-9 expression in osteoblastic cells and HT1080 fibrosarcoma cells.
The histamine H1 receptor (H1R) level is dynamically regulated in vivo under various physiological and pathological conditions. The H1R regulation may consist of various processes, and this study focused on the process of receptor trafficking, that is, receptor internalization to endosomes and the following receptor degradation. First, we identified five possible phosphorylation residues of human H1R, Thr140, Thr142, Ser396, Ser398, and Thr478, based on in vitro phosphorylation studies. Then to determine the role of these residues, we constructed a mutant H1R in which all of these five residues were substituted with alanine. Both wild-type and the mutant receptors expressed in Chinese hamster ovary (CHO) cells had similar values of Kd for [3H]mepyramine binding and Ki for histamine, and these cells showed similar levels of histamine-stimulated inositol phosphate formation. Both types of H1Rs were internalized essentially in the same way upon stimulation with histamine (100 μM) for 30 min. However, down-regulation of the mutant H1R was completely impaired, whereas that of wild-type H1R occurred by approximately 60% by the treatment with 100 μM histamine for 24 h. These results suggest that these residues are responsible for receptor down-regulation but not for receptor internalization. Possibly, phosphorylation of the residues is required for receptor transport from endosomes to lysosomes.
The present study was designed to determine the mechanisms by which serum estradiol levels are enhanced during gonadotropin-induced ovarian development in hypothyroid immature rats. Thyroidectomized (Tx)-immature rats receiving thyroidectomy on day 22 were treated with 8 IU equine chorionic gonadotropin (eCG) at 26 days of age to induce follicular development in ovaries. Ovaries or ovarian granulosa cells were collected on the first proestrus (day 28). Enhanced expression of aromatase (CYP19) mRNA induced by eCG treatment was inhibited by injection of thyroxine (T4: 5 μg × 6 times) in Tx rats. Ovarian granulosa cells harvested from Tx rats were cultured for 24 h in chemically defined serum-free medium containing gonadotropin in the presence of 3,5,3'-triidothyronine (T3). Addition of low doses of T3 (10−8, 10−7 M) to the medium significantly decreased 17β-estradiol (E2) levels, whereas high doses of T3 (10−6, 10−5 M) did not inhibit the levels. Similar effects of T3 on CYP19 mRNA expression were observed. These results indicate that augmentation of E2 production in hypothyroid animals may be mediated, in part, via the stimulation of CYP19 mRNA expression in granulosa cells, which is suppressed by thyroid hormone.
We elucidated the pharmacological properties of a novel nonpeptide vasopressin V2-receptor agonist, OPC-51803 ((5R)-2-[1-(2-chloro-4-(1-pyrrolidinyl)benzoyl-2,3,4,5-tetrahydro-1H-1-benzazepine-5-yl]-N-isopropylacetamide), via both in vitro binding experiments incorporating canine kidney and platelet membrane fractions and in vivo experiments that would determine the compound’s antidiuretic effects after oral administration to water-loaded dogs. OPC-51803 displaced [3H]arginine vasopressin (AVP) binding to canine V2 and V1a receptors, as determined by resulting Ki values of 15.2 ± 0.6 nM (n = 4) and 653 ± 146 nM (n = 4), respectively. These data indicate that OPC-51803 was about 43 times more selective for V2 receptors than for V1a receptors. Antidiuretic studies showed that orally administered doses of OPC-51803 (0.03 to 0.3 mg · kg−1) decreased urine volume and increased urinary osmolality in a dose-dependent manner in water-loaded dogs. Intravenous OPC-51803 infusions (0.3 and 3 μg · kg−1 · min−1) did not affect renal or systemic hemodynamics in anesthetized dogs. Since these results confirm that OPC-51803 shows antidiuretic action in dogs, the compound may be useful for treating AVP-deficient pathophysiological states.
The aim of this study was to investigate the effect of different novel extracts and fractions obtained from Allium sativum (garlic) on in vitro vessel contraction in order to deepen our knowledge of their mechanism of action on vascular reactivity. The contraction induced by noradrenaline (NE, 10−6 or 10−5 M) or KCl (80 mM) was relaxed with all the extracts and fractions studied, but this effect was higher with RG 20-100 (raw garlic fraction) and FG 20-100 (frozen garlic fraction). To increase our understanding of the mechanisms of action of RG 200-100 and FG 200-100, we found their inhibitory actions were retained in the absence of endothelium, whereas inhibition of the entry of extracellular calcium and mobilization of intracellular calcium may play an instrumental role.
In this study, we evaluated whether a specific chymase inhibitor, TY-51184 (2-[4-(5-fluoro-3-methylbenzo[b]thiophen-2-yl)sulfonamido-3-methanesulfonylphenyl]oxazole-4-carboxylicacid), prevents the vascular proliferation in canine grafted veins. In the placebo-and chymase inhibitor-treated groups, the external jugular vein was infiltrated with saline and 10 μM TY-51184, respectively, and then it was grafted to the ipsilateral carotid artery. The non-surgical dogs were used as the control group. By 28 days after grafting, the chymase and ACE activities were significantly increased in the injured arteries. TY-51184 significantly reduced the chymase activity in the grafted veins, while it did not affect the ACE activity. The intimal areas in the placebo- and TY-51184-treated groups were 3.32 ± 0.16 and 1.96 ± 0.52 mm2, respectively, and this difference was significant. The ratios of intimal area to medial area in the placebo- and TY-51184-treated groups were 66.8 ± 3.5% and 34.9 ± 9.2%, respectively, and this difference was also significant. There was a significant relationship between vascular proliferation and chymase activity, but not ACE activity. In this study, we demonstrated that a single treatment with a specific chymase inhibitor, TY-51184, could prevent the vascular proliferation in canine grafted veins.
To clarify heterologous regulation of a receptor is important in considering medication. Histamine constricts the airway smooth muscle through the action to the H1 receptor (H1R), which contributes to asthma. β2-Adrenergic receptor (β2R) agonists are widely used in asthmatic therapy for their bronchodilating effects. In this study, we investigated the effect of β2R activation on the H1R function using Chinese hamster ovary cells stably co-expressing human histamine H1R and β2R (CHO-H1/β2 cell). The stimulation of β2R resulted in the decrease of H1R in the membrane. Heterologous H1R down-regulation was significantly reversed in the presence of the cyclic AMP-dependent protein kinase (PKA) inhibitor KT5720. Since phosphorylation of G protein-coupled receptor (GPCR) by second messenger-dependent kinases, is proposed to be a key step initiating heterologous receptor desensitization, we examined whether heterologous H1R down-regulation was accompanied by H1R phosphorylation. H1R was phosphorylated by β2R stimulation; however, a PKA inhibitor did not inhibit heterologous H1R phosphorylation. Our results suggest that H1R was heterologously regulated by β2R. Not only a direct action of β2R agonist to β2R causing bronchodilation but also indirect action that reduces the number of H1R responsible for bronchoconstriction might contribute to a decrease in the bronchial resistance, which proposes another possible advantage of β2R agonists for asthmatic medication.
A relatively large amount of human liver tissue was required to determine the exact activity of human hepatic CYP3A. Although, the quantity of available human liver tissue samples is limited. We measured levels of CYP3A4 mRNA by RT-PCR with a radiolabeled primer specific for CYP3A4 and compared mRNA expression with CYP3A4 protein level and metabolic activity in liver. The level of CYP3A4 mRNA was correlated with the levels of CYP3A4 protein and activity. Our results suggest that CYP3A4 protein and activity levels can be predicted from CYP3A4 mRNA levels determined by RT-PCR and using a very small amount of liver tissue.