A CLCN1 mutation in dominant myotonia congenita impairs the increment of chloride conductance during repetitive depolarization.

Myotonia congenita is caused by mutation of the CLCN1 gene, which encodes the human skeletal muscle chloride channel (ClC-1). The ClC-1 protein is a dimer comprised of two identical subunits each incorporating its own separate pore. However, the precise pathophysiological mechanism underlying the abnormal ClC-1 channel gating in some mutants is not fully understood. We characterized a ClC-1 mutation, Pro-480-Thr (P480T) identified in dominant myotonia congenita, by using whole-cell recording. P480T ClC-1 revealed significantly slowed activation kinetics and a slight depolarizing shift in the voltage-dependence of the channel gating. Wild-type/mutant heterodimers exhibited similar kinetic properties and voltage-dependency to mutant homodimers. Simulating myotonic discharge with the voltage clamp protocol of a 50 Hz train pulse, the increment of chloride conductance was impaired in both wild-type/mutant heterodimers and mutant homodimers, clearly indicating a dominant-negative effect. Our data showed that slow activation gating of P480T ClC-1 impaired the increment of chloride conductance during repetitive depolarization, thereby accentuating the chloride conductance reduction caused by a slight depolarizing shift in the voltage-dependence of the channel gating. This pathophysiology may explain the clinical features of myotonia congenita.

Presence of GABA(B) receptors forming heterodimers with GABA(B1) and GABA(B2) subunits in human lower esophageal sphincter.

Baclofen, a GABA(B)-receptor (GABA(B)R) agonist has been proposed to be useful as therapeutic agent for the management of gastro-esophageal reflux disease, but whether the compound acts directly at the lower esophageal sphincter (LES) remains to be elucidated. We performed the present study to assess the presence of GABA(B)R in human LES. Western blot analysis showed that both proteins of GABA(B1(a))/GABA(B1(b)) and GABA(B2) subunits were present in the muscle layer of LES. Immunohistochemical findings showed that both GABA(B1)- and GABA(B2)-subunit proteins were located on the neurons within the myenteric plexus, and furthermore, both proteins were observed in the same neurons. Reverse transcriptase-polymerase chain reaction analysis also revealed the presence of mRNAs for both subunits of GABA(B)R and also mRNAs for 6 isoforms of GABA(B1) subunits, from GABA(B1(a)) to GABA(B1(g)), except GABA(B1(d)), in human LES. Thus, the functional GABA(B)R-forming heterodimers with subunits of GABA(B1) and GABA(B2) are located on the myenteric neurons in human LES, suggesting that GABA(B)R agonists and antagonists act at least, at the level of the peripheral nervous system.

Versatile assays for high throughput screening for activators or inhibitors of intracellular proteases and their cellular regulators.

BACKGROUND: Intracellular proteases constitute a class of promising drug discovery targets. Methods for high throughput screening against these targets are generally limited to in vitro biochemical assays that can suffer many technical limitations, as well as failing to capture the biological context of proteases within the cellular pathways that lead to their activation. METHODS #ENTITYSTARTX00026; FINDINGS: We describe here a versatile system for reconstituting protease activation networks in yeast and assaying the activity of these pathways using a cleavable transcription factor substrate in conjunction with reporter gene read-outs. The utility of these versatile assay components and their application for screening strategies was validated for all ten human Caspases, a family of intracellular proteases involved in cell death and inflammation, including implementation of assays for high throughput screening (HTS) of chemical libraries and functional screening of cDNA libraries. The versatility of the technology was also demonstrated for human autophagins, cysteine proteases involved in autophagy. CONCLUSIONS: Altogether, the yeast-based systems described here for monitoring activity of ectopically expressed mammalian proteases provide a fascile platform for functional genomics and chemical library screening.

mu-Opioid receptor forms a functional heterodimer with cannabinoid CB1 receptor: electrophysiological and FRET assay analysis.

Interactions between mu-opioid receptor (muOR) and cannabinoid CB1 receptor (CB1R) were examined by morphological and electrophysiological methods. In baby hamster kidney (BHK) cells coexpressing muOR fused to the yellow fluorescent protein Venus and CB1R fused to the cyan fluorescent protein Cerulean, both colors were detected on the cell surface; and fluorescence resonance energy transfer (FRET) analysis revealed that muOR and CB1R formed a heterodimer. Coimmunoprecipitation and Western blotting analyses also confirmed the heterodimers of muOR and CB1R. [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO) or CP55,940 elicited K+ currents in Xenopus oocytes expressing muOR or CB1R together with G protein activated-inwardly rectifying K+ channels (GIRKs), respectively. In oocytes coexpressing both receptors, either of which was fused to the chimeric Galpha protein Gqi5 that activates the phospholipase C pathway, both DAMGO and CP55,940 elicited Ca2+-activated Cl(-) currents, indicating that each agonist can induce responses through Gqi5 fused to either its own receptor or the other. Experiments with endogenous Gi/o protein inactivation by pertussis toxin (PTX) supported the functional heterodimerization of muOR/CB1R through PTX-insensitive Gqi5(m) fused to each receptor. Thus, muOR and CB1R form a heterodimer and transmit a signal through a common G protein. Our electrophysiological method could be useful for determination of signals mediated through heterodimerized G protein-coupled receptors.

Desensitization of GABA(B) receptor signaling by formation of protein complexes of GABA(B2) subunit with GRK4 or GRK5.

We investigated the role of G protein coupled-receptor kinases (GRKs) in the desensitization of GABA(B) receptor-mediated signaling using Xenopus oocytes and baby hamster kidney (BHK) cells. Baclofen elicited inward K(+) currents in oocytes coexpressing heterodimeric GABA(B) receptor, GABA(B1a) subunit (GB(1a)R) and GABA(B2) subunit (GB(2)R), together with G protein-activated inwardly rectifying K(+) channels (GIRKs), in a concentration-dependent manner. Repetitive application of baclofen to oocytes coexpressing GABA(B)R and GIRKs did not change peak K(+) currents in the first and second responses, but the latter responses were significantly attenuated by coexpression of either GRK4 or GRK5 with attenuation efficacy of GRK4 > GRK5. Coexpression of other GRKs including GRK2, GRK3, and GRK6 had no effect on GABA(B) receptor-mediated desensitization processes. In BHK cells coexpressing GRK4 fused to Venus (brighter variant of yellow fluorescent protein, GRK4-Venus) with GB(1a)R and GB(2)R, GRK4-Venus was expressed in the cytosol but was translocated to the plasma membranes by GABA(B)R activation. In BHK cells coexpressing GRK4 fused to Cerulean (brighter variant of cyan fluorescent protein, GRK4-Cerulean) with GB(1a)R and GB(2)R-Venus, fluorescence resonance energy transfer (FRET) analysis demonstrated that GRK4-Cerulean formed a protein complex with GB(2)R-Venus. Immunoprecipitation and Western blot analysis confirmed GB(2)R-GRK4 complex formation. GRK5 also formed a complex with GB(2)R on the plasma membranes as determined by FRET and Western blotting but not GRK2, GRK3, and GRK6. Our results indicate that GRK4 and GRK5 desensitize GABA(B) receptor-mediated responses by forming protein complexes with GB(2)R subunit of GABA(B)R at the plasma membranes.

Inhibition by selenium compounds of catecholamine secretion due to inhibition of Ca2+ influx in cultured bovine adrenal chromaffin cells.

Selenium is an essential trace metal element, whereas large doses of selenium exert adverse effects to the human body. We examined the effects of selenium compounds, sodium selenite (Na2SeO3) and sodium selenate (Na2SeO4), on catecholamine secretion from cultured bovine adrenal chromaffin cells. Treatment of chromaffin cells with sodium selenite for 72, 48, and 24 h caused decreases in protein and catecholamine contents, in association with cell damage, at concentrations over 30, 300, and 300 microM, respectively. The cells treated with subtoxic conditions (<100 microM, 48 h) of sodium selenite were used for further experiments. Sodium selenite treatment for 48 h inhibited carbachol (CCh)-induced catecholamine secretion in a concentration-dependent and non-competitive manner, while it did not affect high K+- and veratridine-induced catecholamine secretion. Sodium selenite (100 microM) did not affect CCh- and veratridine-induced 22Na+ influx, while the compound inhibited 45Ca2+ influx induced only by CCh, but not high K+ and veratridine. Sodium selenate even at higher concentrations (1000 microM) did not affect any stimulus-induced catecholamine secretion and 45Ca2+ influx. Thus, sodium selenite may specifically exert adverse effects, such as inhibition of physiological stimulus-induced catecholamine secretion from adrenal chromaffin cells due to inhibition of Ca2+ influx.

Acetazolamide acts directly on the human skeletal muscle chloride channel.

Acetazolamide, a carbonic anhydrase inhibitor, is used empirically in neuromuscular diseases with episodic ataxia, weakness, and myotonia, although not all of the mechanisms responsible for its therapeutic effects are understood. To elucidate whether acetazolamide acts directly on the human skeletal muscle voltage-gated chloride channel (ClC-1), which is associated with myotonia, we evaluated the effects of acetazolamide on ClC-1 expressed in cultured mammalian cells, using whole-cell recording. Acetazolamide significantly shifted the voltage dependency of the open probability (P(o)) toward negative potentials in a dose-dependent manner, resulting in an increase of chloride conductance at voltages near the resting membrane potential. This effect was attenuated when using a pipette solution containing 30 mmol/L Hepes. These results suggest that acetazolamide can influence the voltage-dependent opening gate of ClC-1 through a mechanism related to intracellular acidification by inhibiting carbonic anhydrase, and that the therapeutic effects of acetazolamide in neuromuscular diseases may be mediated by activation of ClC-1.

Coupling of GABAB receptor GABAB2 subunit to G proteins: evidence from Xenopus oocyte and baby hamster kidney cell expression system.

Coupling of functional GABAB receptors (GABABR) to G proteins was investigated with an expression system of baby hamster kidney (BHK) cells and Xenopus oocytes. Fluorescence resonance energy transfer (FRET) analysis of BHK cells coexpressing GABAB1a receptor (GB1aR) fused to Cerulean, a brighter variant of cyan fluorescent protein, and GABAB2 receptor (GB2R) fused to Venus, a brighter variant of yellow fluorescent protein, revealed that GB1aR-Cerulean and GB2R-Venus form a heterodimer. The GABABR agonists baclofen and 3-aminopropylphosphonic acid (3-APPA) elicited inward-rectifying K+ currents in a concentration-dependent manner in oocytes expressing GB1aR and GB2R, or GB1aR-Cerulean and GB2R-Venus, together with G protein-activated inward-rectifying K+ channels (GIRKs), but not in oocytes expressing GB1aR alone or GB2R alone together with GIRKs. Oocytes coexpressing GB1aR + Galphai2-fused GB2R (GB2R-Galphai2) caused faster K+ currents in response to baclofen. Furthermore, oocytes coexpressing GB1aR + GB2R fused to Galphaqi5 (a chimeric Galphaq protein that activates PLC pathways) caused PLC-mediated Ca2+-activated Cl- currents in response to baclofen. In contrast, these responses to baclofen were not observed in oocytes coexpressing GB1aR-Galphai2 or GB1aR-Galphaqi5 together with GB2R. BHK cells and Xenopus oocytes coexpressing GB1aR-Cerulean + a triplet tandem of GB2R-Venus-Galphaqi5 caused FRET and Ca2+-activated Cl- currents, respectively, with a similar potency in BHK cells coexpressing GB1aR-Cerulean + GB2R-Venus and in oocytes coexpressing GB1aR + GB2R-Galphaqi5. Our results indicate that functional GABABR forms a heterodimer composed of GB1R and GB2R and that the signal transducing G proteins are directly coupled to GB2R but not to GB1R.

Analysis of the effects of halothane on Gi-coupled muscarinic M2 receptor signaling in Xenopus oocytes using a chimeric G alpha protein.

Metabotropic G protein-coupled receptors have recently been recognized as targets for anesthetics and analgesics. In particular, G(q)-coupled receptors such as muscarinic M(1) receptors (M(1)R) and 5-hydroxytryptamine (5-HT) type 2A receptors have been reported to be targets for anesthetics. Much less is known, however, about the effects of anesthetics on G(i)-coupled receptors. Here we report a method to analyze functions of G(i)-coupled receptors in Xenopus oocytes expressing a chimeric G alpha protein. A chimeric G alpha(q) protein G alpha(qi5), which contains carboxy-terminus five amino acids of G alpha(i), enables G(i)-coupled receptors to couple to Gq-coupled receptor-mediated downstream pathways such as activation of phospholipase C. We determined acetylcholine (ACh)-induced Ca(2+)-activated Cl(-) currents in Xenopus oocytes coexpressing G(i)-coupled muscarinic M(2)receptors (M(2)R) with the chimeric G alpha(qi5). Although ACh did not induce any currents in oocytes expressing M(2)R alone, it caused robust Cl(-) currents in oocytes coexpressing M(2)R with G alpha(qi5). The EC(50) of the ACh-induced Cl(-) current mediated through G alpha(qi5) was 0.2 micromol/l, which was 2.2 times higher than that of the ACh-induced G protein-activated inwardly rectifying K(+) currents activated by G beta gamma subunits liberated from endogenously expressed G alpha(i) in Xenopus oocytes. Other G(i)-coupled somatostatin type 2, 5-HT(1A) and delta-opioid receptors, when coexpressed with G alpha(qi5) in oocytes, also caused robust Ca(2+)-activated Cl(-) currents. In oocytes coexpressing M(2)R and G alpha(qi5), a volatile anesthetic halothane inhibited M(2)R-induced Cl(-) currents in a concentration-dependent manner with the IC(50) of 1.1 mmol/l, suggesting that halothane inhibits M(2)R-induced cellular responses at clinically relevant concentrations. Treatment with the protein kinase C inhibitor GF109203X produced a 3.5-fold enhancement of the initial Cl(-) currents induced by 1 micromol/l ACh in oocytes expressing M(2)R and G(qi5). The rate of halothane-induced inhibition of Cl(-) currents elicited by ACh, however, was not changed in such oocytes pretreated with GF109203X. These findings suggest that halothane inhibits the M(2)R-induced signaling by acting at sites other than PKC activity. Collectively these findings suggest that the use of oocyte expressing G alpha(qi5) would be helpful to examine the effects of anesthetics or analgesics on the function of G(i)-coupled receptors in the Xenopus oocyte expression system.

Isolation of stimulants of gastrointestinal motility in beer.

BACKGROUND: Among various alcoholic beverages, it has reported that beer has a potent activity to stimulate gastric emptying. Our previous studies showed that beer congener stimulated gastrointestinal motility by directly stimulating muscarinic M3 receptor, present in smooth muscles of the gastrointestinal tract. However, active components that account for the action have yet to be identified. We attempted to isolate the stimulant(s) of gastrointestinal motility in beer. METHODS: Beer congener was prepared from beer and used to separate and purify active components by a series of liquid chromatography using affinity to muscarinic M3 receptor as an index. Gastrointestinal motility-stimulating activity was evaluated using a test for activity that causes contraction of longitudinal muscles in guinea pig ileum and a test for gastric emptying activity in mice. RESULTS: The active components (compounds A and B) were purified and isolated from beer by four liquid chromatography steps. The IC50 values of two active isolates to muscarinic M3 receptor were 0.65 x 10 g/ml and 2.30 x 10 g/ml, respectively. The concentrations of compounds A and B contained in beer were sufficient to explain most of the muscarinic M3 receptor binding activity of beer. The active fraction that contained both compounds A and B (which was 10 times as active as beer congener in muscarinic M3 receptor binding activity) dose-dependently contracted the longitudinal muscles of guinea pig ileum with an activity that was 20 times as potent as that of beer congener. The same active fraction significantly stimulated gastric emptying in mice with an activity 20 times as potent as that of beer congener. CONCLUSIONS: Two active components (compounds A and B) were isolated as gastrointestinal motility stimulants (muscarinic M3 agonists) in beer. These results suggest that the two isolated active components are the active entities of the gastrointestinal motility-stimulating effect of beer.

Increases in serum nitrite and nitrate of a few-fold adversely affect the outcome of pregnancy in rats.

The objective of this study was to evaluate serum nitrite and nitrate (nitrite/nitrate) concentrations that affect adversely pregnancy outcome. Pregnant rats, from day 2 to day 8 of pregnancy, were daily given subcutaneously several doses (5, 10, and 30 mg/rat) of diethylenetriamine-nitric oxide (DETA/NO). Serum nitrite/nitrate concentrations were measured using an HPLC system. Serum nitrite/nitrate concentrations increased dose-dependently with DETA/NO. Effects of DETA/NO on pregnancy outcome were assessed on day 14 of pregnancy. In rats given 5 mg DETA/NO, there was a significant increase in serum nitrite/nitrate concentrations (49.2 vs 24.6 micromol/l, P<0.001), and both placental weight and fetal weight decreased compared to control rats. Macroscopic bleeding in placenta was frequently observed in rats given DETA/NO. We further studied effects of DETA/NO on cultured trophoblastic BeWo cells. DETA/NO added to the culture medium increased nitrite/nitrate concentrations in the medium in a dose-dependent manner. Nitrite/nitrate concentrations in the medium over four times the concentration of control decreased progesterone in the medium at 24 h after the application of DETA/NO. The hormonal secretion was not affected by DETA only. This study shows for the first time nitrite/nitrate concentrations affecting adversely pregnancy outcome and function of the trophoblastic cells.

Involvement of G protein betagamma-subunits in diverse signaling induced by G(i/o)-coupled receptors: study using the Xenopus oocyte expression system.

We studied the functions of betagamma-subunits of G(i/o) protein using the Xenopus oocyte expression system. Isoproterenol (ISO) elicited cAMP production and slowly activating Cl(-) currents in oocytes expressing beta(2)-adrenoceptor and the protein kinase A-dependent Cl(-) channel encoded by the cystic fibrosis transmembrane conductance regulator (CFTR) gene. 5-Hydroxytryptamine (5-HT), [d-Ala(2), d-Leu(5)]-enkephalin (DADLE), and baclofen enhanced ISO-induced cAMP levels and CFTR currents in oocytes expressing beta(2)-adrenoceptor-CFTR and 5-HT(1A) receptor (5-HT(1A)R), delta-opioid receptor, or GABA(B) receptor, respectively. 5-HT also enhanced pituitary adenylate cyclase activating peptide (PACAP) 38-induced cAMP levels and CFTR currents in oocytes expressing PACAP receptor, CFTR and 5-HT(1A)R. The 5-HT-induced enhancement of G(s)-coupled receptor-mediated currents was abrogated by pretreatment with pertussis toxin (PTX) and coexpression of G transducin alpha (G(t)alpha). The 5-HT-induced enhancement was further augmented by coexpression of the Gbetagamma-activated form of adenylate cyclase (AC) type II but not AC type III. Thus betagamma-subunits of G(i/o) protein contribute to the enhancement of G(s)-coupled receptor-mediated responses. 5-HT and DADLE did not elicit any currents in oocytes expressing 5-HT(1A)R or delta-opioid receptor alone. They elicited Ca(2+)-activated Cl(-) currents in oocytes coexpressing these receptors with the Gbetagamma-activated form of phospholipase C (PLC)-beta2 but not with PLC-beta1. These currents were inhibited by pretreatment with PTX and coexpression of G(t)alpha, suggesting that betagamma-subunits of G(i/o) protein activate PLC-beta2 and then cause intracellular Ca(2+) mobilization. Our results indicate that betagamma-subunits of G(i/o) protein participate in diverse intracellular signals, enhancement of G(s)-coupled receptor-mediated responses, and intracellular Ca(2+) mobilization.

Characterization of GABA(B) receptors involved in inhibition of motility associated with acetylcholine release in the dog small intestine: possible existence of a heterodimer of GABA(B1) and GABA(B2) subunits.

Characterization of the gamma-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 GABA(B) receptor, GABA(B1) and GABA(B2), in the dog small intestine, although GABA(B1) subunits were 6 isoforms of GABA(B1) (GABA(B1(a)) - GABA(B1(g))), except GABA(B1(d)). Thus, the GABA(B) receptor located at cholinergic neurons as a heterodimer with subunits of GABA(B1) and GABA(B2) in the dog small intestine operates predominantly relative to the GABA(A) receptor in physiological motility.

Characterization of GABAB receptor in the human colon.

Characterization of the GABA(B) receptor in the human colon was performed by the reverse transcription-polymerase chain reaction (RT-PCR). mRNAs for both subunits of the GABA(B) receptor, GABA(B1) and GABA(B2), were detected in the human colon. The GABA(B1(e)) isoform was detected in the human colon, but not in the brain, and the other isoforms, except GABA(B1(d)), were detected in both tissues. Thus, the GABA(B) receptor may be present as a heterodimer with subunits of GABA(B1) and GABA(B2) in the human colon.

Site of action of the general anesthetic propofol in muscarinic M1 receptor-mediated signal transduction.

Although a potential target site of general anesthetics is primarily the GABA A receptor, a chloride ion channel, a previous study suggested that the intravenous general anesthetic propofol attenuates the M1 muscarinic acetylcholine receptor (M1 receptor)-mediated signal transduction. In the present study, we examined the target site of propofol in M1 receptor-mediated signal transduction. Two-electrode voltage-clamp method was used in Xenopus oocytes expressing both M1 receptors and associated G protein alpha subunits (Gqalpha). Propofol inhibited M1 receptor-mediated signal transduction in a dose-dependent manner (IC50 = 50 nM). Injection of guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) into oocytes overexpressing Gqalpha was used to investigate direct effects of propofol on G protein coupled with the M1 receptor. Propofol did not affect activation of Gqalpha-mediated signal transduction with the intracellular injection of GTPgammaS. We also studied effects of propofol on l-[N-methyl-3H]scopolamine methyl chloride ([3H]NMS) binding and M1 receptor-mediated signal transduction in mammalian cells expressing M1 receptor. Propofol inhibited the M1 receptor-mediated signal transduction but did not inhibit binding of [3H]NMS. Effects of propofol on Gs- and Gi/o-coupled signal transduction were investigated, using oocytes expressing the beta2 adrenoceptor (beta2 receptor)/cystic fibrosis transmembrane conductance regulator or oocytes expressing the M2 muscarinic acetylcholine receptor (M2 receptor)/Kir3.1 (a member of G protein-gated inwardly rectifying K(+) channels). Neither beta2 receptor-mediated nor M2 receptor-mediated signal transduction was inhibited by a relatively high concentration of propofol (50 microM). These results indicate that propofol inhibits M1 receptor-mediated signal transduction by selectively disrupting interaction between the receptor and associated G protein.

Role of endothelin ETA and ETB receptors in the guinea-pig urinary bladder contraction.

The distribution and function of endothelin receptors in the guinea-pig urinary bladder were examined. Specific [125I]endothelin-1 binding sites with both the endothelin ET(A) and ET(B) receptor subtypes were distributed in the muscle layer. Endothelin-1 elicited a tonic contraction which was inhibited by cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ123) but not by N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine (BQ788) and which was inhibited more strongly by a combination of BQ123 and BQ788. Sarafotoxin S6c elicited a contraction which was abolished by BQ788. The concentration of endothelin-1 in the muscle layer was 707.0+/-67.5 pg/g wet weight. Thus, endothelin-1 may regulate muscle tone via both subtypes of endothelin receptors in an autocrine manner in the guinea-pig urinary bladder.

Involvement of 5-hydroxytryptamine4 receptor in the exacerbation of neuronal loss by psychological stress in the hippocampus of SHRSP with a transient ischemia.

A transient forebrain ischemia produced a delayed neuronal death of the hippocampus pyramidal cells in stroke-prone spontaneously hypertensive rats (SHRSP). Long term exposure of rats to stress has been reported to induce deleterious effects on the brain including morphological neuronal degeneration in the hippocampus. The present study was designed to examine the effects of psychological and physical stress on the ischemia-related neuronal death and the effects of 5-hydroxytryptamine(4) (5-HT(4)) receptor antagonist. SHRSP were exposed to the psychological or physical stress for 60 min in the communication box once or repeatedly for 3 days and occluded. SB204070, a 5-HT(4) receptor antagonist was injected before the occlusion. Seven days after the occlusion, the number of the neurons damaged morphologically was examined. A transient bilateral carotid occlusion produced a neuronal death of the CA1 subfield of the hippocampus in a time-dependent manner between 3 and 10 min. A 4 min occlusion induced very little morphological damage and a 5 min one produced a significant neuronal death. Exposure of rats to the psychological stress during 60 min for 3 days before the ischemic insults damaged the pyramidal cells by 4 min ischemia much more than without stress. Physical stress daily for 3 times also increased the damaged neurons. Pretreatment of SB204070 0.1 mg/kg after the stress exposure for 3 days significantly decreased the neuronal damage exacerbated by the stress exposure; however, it did not alter the damage induced by 4 or 10 min occlusion without stress. These results suggest that the repeated exposure of animals to the stress dramatically exacerbates the neuronal death by a transient ischemia and the 5-HT(4) receptor may be involved in the stress-induced exacerbating mechanism of the neuronal damage.

[Functional difference of prokinetics depending on subtypes and localization of receptor in alimentary tract].

Interaction of function and localization of receptors, especially the 5-hydroxytryptamine4 (5-HT4) receptor was examined in relation to the motility of gastrointestinal tract. The responses mediated by stimulation of 5-HT4 receptor appear to differ with different localization of receptor. The 5-HT4 receptor-mediated acceleration of acetylcholine (ACh) release in the preparations isolated from gastric antrum and corpus, but not fundus, of guinea pig corresponded to the presence of 5-HT4 receptor in the myenteric plexus. The 5-HT4 receptor-mediated response was predominant in the 5-HT-induced acceleration of motility associated with ACh release in the intestine of the whole body of dogs, and the 5-HT4 receptor was localized on the myenteric plexus of dog intestine. Local administration of GABA into intestinal marginal artery reduced the motility associated with ACh release in the intestine of whole body of dogs, and thus response via the inhibitory GABAB receptor was more predominant than that via excitatory GABAA receptor. The GABAB receptor is the first G protein-coupled receptor discovered to form heterodimers, consisted of GABAB1 and GABAB2. There are isoforms of GABAB1, from GABAB1(a) to GABAB1(g), and therefore the function and localization of the GABAB receptor may vary with the different isoforms of GABAB1.

Identification of human Kir2.2 (KCNJ12) gene encoding functional inward rectifier potassium channel in both mammalian cells and Xenopus oocytes.

Arginine residue at position 285 (R285) in the intracellular C-terminal domain of inward rectifier potassium channel Kir2.2 is conserved in many species, but missing in previously reported human Kir2.2 sequences. We here identified the human Kir2.2 gene in normal individuals, which contained R285 in the deduced amino-acid sequence (hKir2.2/R285). All 30 individuals we examined were homozygous for Kir2.2/R285 gene. The hKir2.2/R285 was electrophysiologically functional in both mammalian cells and Xenopus oocytes. However, the hKir2.2 missing R285 was functional only in Xenopus oocytes, but not in mammalian cells. Thus, R285 in Kir2.2 is important for its functional expression in mammalian cells.

Involvement of cholinergic neurons in orexin-induced contraction of guinea pig ileum.

The mechanism underlying orexin-induced contraction was examined in isolated preparations of guinea pig ileum, in relation to cholinergic transmission. Orexin-A caused contraction of ileal strips in a concentration-dependent manner. 1-(2-Methylbenzoxazol-6-yl)-3-[1,5]napthyridin-4-yl-urea hydrochloride (SB-334867-A) antagonized the orexin-A-induced contraction, with no effects on the acetylcholine-induced contraction and twitch contractions. The orexin-A-induced contraction was inhibited by tetrodotoxin and atropine, but not by hexamethonium, an antagonist of vasoactive intestinal peptide and a mixture of 5-hydroxytryptamine receptor antagonists. Orexin-A evoked an outflow of [3H]acetylcholine from the ileal strips preincubated with [3H]choline, in a concentration-dependent manner, and the orexin-A-evoked outflow was inhibited by tetrodotoxin, indicating that the outflow of [3H]acetylcholine originates from the nerve terminals. The orexin-A-evoked outflow of [3H]acetylcholine was antagonized by SB-334867-A. Thus, orexin-A evokes the release of acetylcholine from the enteric cholinergic neurons due to stimulation of the orexin-1 receptors and then causes contractions of guinea pig ileum.