Biomedical subjects
Publications and source records attributed to Kenji Sakamoto.
An organoborate zwitterion-lithium salt mixture, prepared via selective borate formation of N-ethylimidazolium salt, exhibited ionic conductivity of 3.0 x 10(-5) S cm(-1) at 50 degrees C and a lithium transference number of 0.69.
The aim of the present study is to investigate difference in sensitivity to glibenclamide, a sulfonylurea oral antidiabetic agent, among Wistar rats, Spontaneously Hypertensive rats (SHR/Izm) and Wistar-Kyoto rats (WKY/Izm). We examined the effect of glibenclamide on blood levels of glucose and insulin in these rat strains. Under anesthesia with pentobarbital sodium (50 mg/kg, i.p.), blood samples were collected before and 5-120 min after administration of glibenclamide (10 mg/kg, i.p.). Blood levels of glucose and insulin in each sample were measured by glucose oxidase method and radioimmunoassay, respectively. In 8 week-old rats of all strains tested, blood levels of glucose were decreased by glibenclamide. In 12-20-week-old rats, although blood levels of glucose in Wistar and SHR/Izm were decreased after glibenclamide administration, those of WKY/Izm were not decreased. In rats of this age, time-course and extent of increases in blood insulin levels observed after administration of glibenclamide in WKY/Izm was almost the same as that of SHR/Izm, however, smaller than that of Wistar. Both insulin secretions induced via inactivation of ATP-sensitive K+ channel and sensitivity of pancreatic beta-cells to insulin seems to be decreased in WKY/Izm after 12 weeks of age. This phenomenon may explain the mechanism of glucose intolerance previously reported in WKY/Izm.
Long-period fiber Bragg gratings fabricated by exposure of hydrogen-loaded fiber to UV laser light exhibit large-scale dynamic evolution for approximately two weeks at room temperature. During this time two distinct features show up in their spectrum: a large upswing in wavelength and a substantial deepening of the transmission minimum. The dynamic evolution of the transmission spectrum is explained quantitatively by use of Malo's theory of UV-induced quenching [Electron. Lett. 30, 442 (1994)] followed by refilling of hydrogen in the fiber core and the theory of hydrogen diffusion in the fiber material. The amount of hydrogen quenched by the UV irradiation is 6% of the loaded hydrogen.
Stimulation of the histamine H1 receptor has been shown to enhance adenosine 3', 5'-cyclic monophosphate (cAMP) accumulation in various cell types but, to date, the mechanism by which this occurs is still unclear. In the present study, we examined the possibility that the betagamma subunits of G proteins (G betagamma) are involved in this process in cultured Chinese hamster ovary cells transfected with the human histamine H1 receptor (CHO-H1). Histamine increased intracellular cAMP levels in a concentration-dependent manner in CHO-H1 cells, and this histamine action was abolished by pyrilamine (1 microM). Inhibition of histamine H1 receptor-G(q) protein coupling by stable expression of the C-terminal peptide of G alpha(q) protein significantly attenuated the cAMP accumulation induced by histamine. By comparison, neither BAPTA/AM (50 microM), an intracellular Ca2+ chelator, nor GF 109203X (1 microM), an inhibitor of protein kinase C, influenced the cAMP response. Histamine H1 receptor-mediated cAMP accumulation was significantly inhibited by transient transfection of CHO-H1 cells with the C-terminal peptide of beta-adrenoceptor kinase I (residues 542-685), a scavenger of G betagamma. Stable expression of the C-terminal peptide of the G alpha(s) protein, but not treatment with pertussis toxin (200 ng/ml for 24 h), attenuated the histamine H1 receptor-mediated cAMP accumulation. These results suggest that stimulation of histamine H1 receptors activates adenylyl cyclase through the release of G betagamma subunits from G proteins, thereby elevating intracellular cAMP levels.
Brief ischemia was reported to protect retinal cells against injury induced by subsequent ischemia-reperfusion with de novo protein synthesis, and this phenomenon is known as late ischemic preconditioning. The aims of the present study were to determine whether nitric oxide synthase (NOS) was involved in the mechanism of late ischemic preconditioning in rat retina using pharmacological tools. Under anesthesia with pentobarbital sodium, male Sprague-Dawley rats were subjected to 60 min of retinal ischemia by raising intraocular pressure to 130 mm Hg. Ischemic preconditioning was achieved by applying 5 min of ischemia 24 hrs before 60 min of ischemia. Retinal sections sliced into 5 microm thick were examined 7 days after ischemia. Additional groups of rats received NG-nitro-L-arginine and NG-monomethyl-L-arginin, non-selective NO synthase inhibitors, 7-nitroindazole, a neuronal NOS inhibitor, and aminoguanidine and L-N6-(1-iminoethyl) lysine, inducible NO synthase (iNOS) inhibitors before preconditioning, and were subjected to 60 min of ischemia. In the non-preconditioned group, cell loss in the ganglion cell layer and thinning of the inner plexiform and inner nuclear layer were observed 7 days after 60 min of ischemia. Ischemic preconditioning for 5 min completely protected against the histological damage induced by 60 min of ischemia applied 24 hrs thereafter. Treatment of rats with aminoguanidine and L-N6-(1-iminoethyl) lysine, but not NG-nitro-L-arginine, NG-monomethyl-L-arginine or 7-nitroindazole, wiped off the protective effect of ischemic preconditioning. The inhibitory effect of aminoguanidine was abolished by L-arginine, but not D-arginine. The results in the present study suggest that NO synthesized by iNOS is involved in the histological protection by late ischemic preconditioning in rat retina.
The physicochemical properties of the H(2)O molecules adsorbed on TiO(2) surfaces during UV light irradiation were fully investigated by near-infrared (NIR) absorption spectroscopy. It was found that the H(2)O molecules adsorbed on the TiO(2) surfaces desorb during UV light irradiation by the heating effect of the light source. Since the amount of the H(2)O adsorbed on the TiO(2) surfaces decreased, the distribution of the hydrogen bonds within the H(2)O molecules decreased, resulting in a decrease in the surface tension of the H(2)O clusters. The decrease in the surface tension of H(2)O under UV light irradiation was found to be one of the most important driving forces in which the H(2)O clusters on the TiO(2) surface spread out thermodynamically, forming H(2)O thin layers. The partial elimination of the hydrocarbons from the TiO(2) surface by the photocatalytic complete oxidation was seen to be the other important factor, providing free spaces on the surface where the H(2)O clusters could spill over and spread out to form the thin H(2)O layers. Moreover, the temperature changes of the TiO(2) powder samples during UV light irradiation were found to show a good correspondence with the changes in the contact angle of the H(2)O droplets on the TiO(2) thin film surfaces. Especially the time scale for the hydrophilic conversion on the TiO(2) surfaces under UV light irradiation was in good agreement with the decrease in the amount of H(2)O molecules adsorbed on the TiO(2) surfaces but not the amount of the hydrocarbons eliminated by the photocatalytic oxidation reactions, showing that the adsorption and desorption of H(2)O molecules are generally quite sensitive to the temperature changes of solid surfaces.
Physical properties of liquid imidazole-borane complex were investigated to demonstrate their utility as aprotic polar solvents or liquid electrolytes appropriate for selective ion transport.
Brief ischemia was reported to protect various cells against injury induced by subsequent ischemia-reperfusion, and this phenomenon is known as ischemic preconditioning. The aims of the present study were to clarify whether early ischemic preconditioning could be observed in the rat retina by histological examination. Male Sprague-Dawley rats were subjected to 60 min of retinal ischemia by raising intraocular pressure to 130 mm Hg. Ischemic preconditioning was achieved by applying 5 min of ischemia 5-60 min before 60 min of ischemia. Additional groups of rats received 10 mg/kg 8-phenyltheophiline and 4.5 mg/kg 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), adenosine A1 receptor antagonists, 5 mg/kg 5-hydroxydecanoate and 1 mg/kg glibenclamide, ATP-sensitive K+ channel blockers, or 2.5 mg/kg chelerythrine and 0.1 mg/kg bisindolylmaleimide I, protein kinase C inhibitors, 15 or 30 min before preconditioning. In the non-preconditioned group, cell loss in the ganglion cell layer and thinning of the inner plexiform and inner nuclear layer were observed 7 days after 60 min of ischemia. Five minutes of preconditioning ischemia 20-40 min before 60 min of sustained ischemia completely prevented the retinal tissue damage induced by the sustained ischemia. Treatment with 8-phenyltheophylline, DPCPX, 5-hydroxydecanoate, glibenclamide, chelerythrine and bisindolylmaleimide I almost completely reduced the protective effect of early ischemic preconditioning. The results in the present study indicated that early ischemic preconditioning was demonstrated in the rat retina. Stimulation of adenosine receptors, opening of ATP-sensitive K+ channels and activation of protein kinase C might be involved in the underlying protective mechanisms.
We characterized the beta-adrenoceptor-blocking property of mexiletine, a class Ib antiarrhythmic drug, on Chinese hamster ovary (CHO) cells stably expressing cloned human beta1-, beta2-, and beta3-adrenoceptors. In radioligand binding experiments, mexiletine (10 microM-1 mM) concentration-dependently displaced the specific binding of [125I]cyanopindolol to human beta1- and beta2-adrenoceptors in the membrane fraction of the cells. High concentration (100 microM-1 mM) of mexiletine partially displaced the specific binding of [125I]cyanopindolol to human beta3-adrenoceptor. On the other hand, high concentration (300 microM and 1 mM) of lidocaine, another class Ib antiarrhythmic drug, partially displaced the specific binding of [125I]cyanopindolol to human beta1-adrenoceptor, whereas it did not affect the specific binding of [125I]cyanopindolol to human beta2- and beta3-adrenoceptors. Mexiletine (5, 50, and 500 microM) reduces basal adenosine 3',5'-cyclic monophosphate (cAMP) level and isoprenaline-induced cAMP accumulation on CHO cells stably expressing cloned human beta1- and beta2-adrenoceptors. Lidocaine (10 and 100 microM and 1 mM) tend to reduce basal cAMP level on CHO cells stably expressing cloned human beta1-adrenoceptors, whereas the drug did not reduce the isoprenaline-induced cAMP accumulation on CHO cells stably expressing cloned human beta1-, beta2-, and beta3-adrenoceptors. Mexiletine and lidocaine have no effect on forskolin (0.1, 1, and 3 microM)-induced cAMP accumulation. These results demonstrate that mexiletine blocks the binding of agonists to beta1- and beta2-adrenoceptors, and thereby attenuates the agonist-induced cAMP accumulation, and that the action of mexiletine as an antagonist of beta1- and beta2-adrenoceptors is independent of its antiarrhythmic property.
We examined the effect of diphenylamine-2-carboxylic acid (DPC), which has been shown to inhibit the efflux of cyclic nucleotides from vascular smooth-muscle cells, on the relaxant responses to forskolin, an adenylyl cyclase activator, and sodium nitroprusside (SNP), an NO donor, in the porcine coronary arteries. DPC (100 microM), which caused only a minor effect by itself, significantly augmented the relaxant responses to forskolin and SNP in the preparations contracted with 30 mM KCl. On the other hand, DPC did not affect the relaxant responses to nifedipine and cromakalim. Forskolin (10 microM) induced an accumulation of adenosine 3', 5'-cyclic monophosphate (cAMP) in the porcine coronary arteries, which was associated with an accumulation of cAMP in the incubation media. The intracellular cAMP response to forskolin was enhanced by DPC, whereas the extracellular cAMP response was reduced. The effects of SNP on guanosine 3', 5'-cyclic monophosphate (cGMP) accumulation were examined in the presence of 3-isobutyl-l-methylxanthine (500 microM) because cGMP was not found in the tissue and the incubation medium in the absence of the phosphodiesterase inhibitor. DPC significantly decreased the SNP-induced release of cGMP to the extracellular space, whereas it did not affect the accumulation of cGMP in the tissue. These results suggest that DPC inhibits the efflux of cyclic nucleotides. It is likely that the inhibitory effect of DPC on cAMP efflux contributes to the enhancement of tissue cAMP accumulation and relaxation produced by the agents that activate adenylyl cyclase. Thus, the transport system(s) of cyclic nucleotides may be a novel target for the prevention and/or treatment of various cardiovascular diseases.
We examined the basal adenosine 3',5'-cyclic monophosphate (cAMP) levels and forskolin-induced cAMP accumulation in cultured Chinese hamster ovary cells (CHO) expressing different levels of human beta(2)-adrenoceptors. Both the basal and forskolin-induced cAMP accumulation in the cells that express higher density of beta(2)-adrenoceptors (CHO-beta(2)/H; 560 fmol/mg protein) were larger than those in the cells that express lower density of beta(2)-adrenoceptors (CHO-beta(2)/L; 270 fmol/mg protein). In addition, isoproterenol-induced cAMP accumulation was also augmented as the number of beta(2)-adrenoceptors was increased. ICI 118,551, a selective beta(2)-adrenoceptor antagonist with inverse agonist properties, decreased all the levels of cAMP observed in both cell lines. These results suggest that the agonist-independent (constitutive) activity of beta(2)-adrenoceptors plays a key role in the control of forskolin-induced cAMP accumulation.
MaxiK channel, the large-conductance Ca2+-sensitive K+ channel, facilitates a negative feedback mechanism to oppose excitation and contraction in various types of smooth muscles including urinary bladder smooth muscle (UBSM). In this study, we investigated how the contribution of MaxiK channel to the regulation of basal UBSM mechanical activity is altered in streptozotocin-induced diabetic rats. Although the urinary bladder preparations from both control and diabetic rats were almost quiescent in their basal mechanical activities, they generated spontaneous rhythmic contractions in response to a MaxiK channel blocker, iberiotoxin (IbTx). The effect of IbTx on the mechanical activity was significantly greater in diabetic rat than in control animal. Similarly, the basal mechanical activity was increased with apamin, an inhibitor for some types of small conductance Ca2+-sensitive K+ channels, and this effect was more pronounced for diabetic rat. However, in both control and diabetic animals, IbTx action was stronger than that of apamin. Diabetes also enhanced the responses to BayK 8644, an L-type Ca2+ channel agonist. The extent of this enhancement in diabetic bladder vs. control was, however, almost the same as that attained with IbTx. Expression levels for MaxiK channel as well as apamin-sensitive K+ channels and L-type Ca2+ channel were not altered by diabetes, when determined as their corresponding mRNA levels. These results indicate that diabetes can potentially increase the basal UBSM mechanical activity. However, in diabetic UBSM, the main negative-feedback system triggered by MaxiK channel is still preserved enough to counteract the possible enhancement of this smooth muscle mechanical activity.
Protease-activated receptor-2 (PAR-2) is activated by serine proteases, such as trypsin and mast cell tryptase. Recently, we have shown that activators of PAR-2 contract the rat urinary bladder mainly by stimulating release of prostaglandins (PGs) from the mucosal layer. In the present study, we investigated how the PAR-2-mediated responses are altered in rats with cyclophosphamide (CYP)-induced cystitis. The contractile responses to trypsin and PAR-2 activating peptide (PAR-2 AP; SLIGRL-NH2) in the urinary bladders were augmented by treatment of rats with CYP. The contractile effects of these PAR-2 activators on the smooth muscles of the urinary bladder were also potentiated after induction of cystitis by CYP. On the other hand, CYP-induced cystitis significantly attenuated contractions produced by PGE2 in the smooth muscles of the urinary bladder. The PAR-2-mediated contractions were significantly prevented by indomethacin or NS-398, an inhibitor of cyclooxygenase-2. Both trypsin and PAR-2 AP increased the release of PGE2 from the urinary bladder mucosa and smooth muscle. CYP-induced cystitis enhanced the PAR-2 activators-induced PGE2 releases from the urinary mucosa without affecting those from the smooth muscle of the urinary bladder. The PGE2 releases were prevented by indomethacin or NS-398. The mRNAs for PAR-2 in the urinary bladder mucosa and smooth muscle preparations were not altered in CYP-induced cystitis. These results suggest that PAR-2-mediated responses were enhanced in bladders from CYP-treated rats. The enhancement of PAR-2-mediated contraction might be ascribed to the increased production of PGs and the altered sensitivity of smooth muscle to PAR-2 activators.
Effects of 4-(3-chlorophenyl)-1,7-diethylpyrido[2,3-d]pyrimidin-2(1H)-one (YM976), a novel and selective phosphodiesterase type 4 inhibitor, on tension and adenosine 3',5'-cyclic monophosphate (cAMP) content of bovine tracheal smooth muscle were compared with those of rolipram and theophylline. YM976, rolipram and theophylline relaxed the tracheal preparations contracted with histamine in a concentration-dependent manner. The relaxant effects of YM976 and rolipram were more potent than those of theophylline. These phosphodiesterase inhibitors-induced relaxations were dramatically diminished when tracheal smooth muscle was contracted with methacholine instead of histamine. Pretreatment of the tracheal preparations with YM976 (10 microM) or rolipram (10 microM), but not with theophylline (1 mM), shifted the concentration-response curves for contractile responses to histamine; however, the same procedure failed to affect concentration-response relationships for methacholine-induced contractions. At 1 and 10 microM, both YM976 and rolipram increased the tissues cAMP content. These results suggest that YM976 relaxes tracheal smooth muscle, probably through the cAMP-dependent mechanism.
We examined how lidocaine affects muscarinic receptor-mediated inhibition of adenylyl cyclase in bovine tracheal smooth muscles. Lidocaine (100 microM) augmented the relaxant responses to forskolin in the bovine tracheal smooth muscle contracted with methacholine (0.3 microM). On the other hand, lidocaine failed to affect the relaxant effects of forskolin on the histamine (100 microM)- and KCl (40 mM)-contracted preparations. Lidocaine (100 microM) enhanced both basal and forskolin-stimulated cAMP accumulation in the presence of methacholine (0.3 microM). However, in the absence of methacholine, neither basal nor forskolin-stimulated cAMP accumulation was affected by lidocaine. Similar phenomenon was observed when the bovine tracheal smooth muscles were treated with methoctramine (0.03 microM). In radioligand binding experiments, lidocaine inhibited [3H]N-methyl scopolamine binding to cloned human muscarinic receptors (M(1)-M(5)) expressed in Chinese hamster ovary cells. These results suggest that lidocaine prevents muscarinic receptor-mediated signaling pathway and thereby reverses inhibition of adenylyl cyclase by methacholine in bovine tracheal smooth muscle.
Possible involvement of Ca(2+)-independent phospholipase A2 (iPLA2) was examined in protease-activated receptor-2 (PAR-2)-mediated contraction of the rat urinary bladder. Both PAR-2 activating peptide (PAR-2 AP; SLIGRL-NH2) and trypsin produced a concentration-dependent contractile response in the urinary bladder preparations. These contractions were significantly (p<0.01) attenuated by indomethacin (10 microM), an inhibitor of cyclooxygenase, or bromoenol lactone (BEL; 10 micro M), an inhibitor of iPLA2. On the other hand, the contractile responses to bradykinin were not significantly affected by BEL, although they were reduced by indomethacin. Arachidonyltrifluoromethyl ketone (AACOCF3; 30 microM), an inhibitor of cytosolic Ca(2+)-dependent phospholipase A2, did not affect the trypsin- and bradykinin-induced contractions. Both indomethacin and BEL had no inhibitory effect on the prostaglandin E2-induced contractions. These results suggest that PAR-2 activators and bradykinin stimulate the release of prostaglandins and thereby contract the rat urinary bladder smooth muscles. The release of prostaglandins by PAR-2 activators seems to be partly mediated by the iPLA2.
This study examines the effects of inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) on acetylcholine (ACh)-induced contraction in rat urinary bladder smooth muscle. Neostigmine, a non-selective ChE inhibitor, caused concentration-dependent contractions in rat urinary bladder strips, whereas tetraisopropylpyrophosphoramide (iso-OMPA; a BuChE inhibitor) failed to affect the resting tone of the preparations. Neostigmine (1 microM) markedly augmented the contractile responses to ACh. Although iso-OMPA (10 microM) also potentiated ACh-induced contraction, the effect was less than that evoked by neostigmine. The activities of AChE in rat urinary bladder strips were significantly (P<0.05) higher than those of BuChE. These results indicated that AChE, rather than BuChE, plays an important role in controlling ACh-induced contractions of rat urinary bladder.
We examined how diabetes affects the beta-adrenoceptor subtypes mediating relaxation of rat urinary bladder smooth muscle contracted with carbachol. The relaxant responses to isoproterenol were larger in muscles from rats 8 to 10 weeks after induction of diabetes with streptozotocin (80 mg/kg, i.p.) as compared to the control muscles. In contrast, forskolin-induced relaxations did not differ significantly in the control and diabetes groups. Propranolol (1 microM) abolished the diabetes-induced augmentation of relaxant responses to isoproterenol. The relaxant responses to T-0509 ((-)-(R)-1-(3,4-dihydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)-amino]ethanol hydrochloride), a beta(1)-adrenoceptor agonist, were small but significantly augmented by diabetes. On the other hand, diabetes did not change the relaxations produced by clenbuterol, a beta(2)-adrenoceptor agonist, and BRL37344 ((+/-)-(R*,R*)-(4-[2-([2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]phenoxy)acetic acid), a beta(3)-adrenoceptor agonist. These results suggest that diabetes selectively augments the beta(1)-adrenoceptor-mediated relaxation of the rat urinary bladder smooth muscle.