Mild acute intestinal inflammation induced by DSS can be inhibited by 4-CA and this action is associated with the suppression of COX-2 expression and activity.

Abstract. Interactions between μ-opioid receptor (μOR) and cannabinoid CB 1 receptor (CB 1 R) were examined by morphological and electrophysiological methods. In baby hamster kidney (BHK) cells coexpressing μOR fused to the yellow fluorescent protein Venus and CB 1 R fused to the cyan fluorescent protein Cerulean, both colors were detected on the cell surface; and fluorescence resonance energy transfer (FRET) analysis revealed that μOR and CB 1 R formed a heterodimer. Coimmunoprecipitation and Western blotting analyses also confirmed the heterodimers of μOR and CB 1 R. [D-Ala 2 ,N-Me-Phe 4 ,Gly 5 -ol]enkephalin (DAMGO) or CP55,940 elicited K + currents in Xenopus oocytes expressing μOR or CB 1 R together with G protein activated-inwardly rectifying K + channels (GIRKs), respectively. In oocytes coexpressing both receptors, either of which was fused to the chimeric Gα protein G qi5 that activates the phospholipase C pathway, both DAMGO and CP55,940 elicited Ca 2+ -activated Cl − currents, indicating that each agonist can induce responses through G qi5 fused to either its own receptor or the other. Experiments with endogenous G i/o protein inactivation by pertussis toxin (PTX) supported the functional heterodimerization of μOR/ CB 1 R through PTX-insensitive G qi5(m) fused to each receptor. Thus, μOR and CB 1 R 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.

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The multiple 5-hydroxytryptamine (5-HT, serotonin) receptor subtypes are distinguished. In this article, we described mainly the 5-HT4 receptor of four subtypes of functional 5-HT receptors, 5-HT1, 5-HT2, 5-HT3, and 5-HT4, recognized in the gastrointestinal tract. In-vivo microdialysis experiments determined that activation of the 5-HT4 receptor stimulated intestinal motor activity associated with a local increase in acetylcholine (ACh) release from the intestinal cholinergic neurons in the whole body of dogs. The 5-HT4 receptor-mediated response of ACh release in the antral, corporal, and fundic strips isolated from guinea pig stomach corresponds to the presence of 5-HT4 receptor in the myenteric plexus. In-vitro receptor autoradiograms of the stomach and colon indicate that the distribution of 5-HT4 receptors in human tissues is similar to that in the guinea pig, although density of 5-HT4 receptors in the myenteric plexus of human tissues is lower than that in guinea pig tissues. The 5-HT4 receptors located in the myenteric plexus may participate in gastrointestinal motility, and thus the 5-HT4 agonists and antagonists may be available for treatment of dysfunction of gastrointestinal motility.

We investigated the inactivation process of macroscopic cardiac L-type Ca(2+) channel currents using the whole cell patch-clamp technique with Na(+) as the current carrier. The inactivation process of the inward currents carried by Na(+) through the channel consisted of two components >0 mV. The time constant of the faster inactivating component (30.6 +/- 2.2 ms at 0 mV) decreased with depolarization, but the time constant of the slower inactivating component (489 +/- 21 ms at 0 mV) was not significantly influenced by the membrane potential. The inactivation process in the presence of isoproterenol (100 nM) consisted of a single component (538 +/- 60 ms at 0 mV). A protein kinase inhibitor, H-89, decreased the currents and attenuated the effects of isoproterenol. In the presence of cAMP (500 microM), the inactivation process consisted of a single slow component. We propose that the faster inactivating component represents a kinetic of the dephosphorylated or partially phosphorylated channel, and phosphorylation converts the kinetics into one with a different voltage dependency.

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1. Effect of (-)-epigallocatechin-3-O-gallate (EGCG), a condensed tannin isolated from green tea leaves, on the life span and hypertensive lesions in the stroke-prone spontaneously hypertensive rat (SHRSP) was compared with that of persimmon tannin.2. Long-term administration of either 0.5% EGCG or 0.5% persimmon tannin to SHRSP inhibited the incidence of stroke and prolonged the life span, but did not affect the blood pressure.3. These results indicate that EGCG may prevent incidence of stroke due to the radical scavenging action and inhibition of lipid peroxidation, and may result in prolonging the life span of SHRSP, as in the case of persimmon tannin.

Homologous desensitization of G protein-coupled receptors involves agonist-dependent phosphorylation of receptors by G protein-coupled receptor kinases (GRKs). To identify GRK(s) that play a role in homologous desensitization of the thyrotropin (TSH) receptor, thyroid cDNA was amplified by polymerase chain reaction using degenerate oligonucleotide primers from highly conserved regions in GRK family. GRK5 is found in the predominant isoform expressed in the thyroid. Rat GRK5 cDNA was then isolated, which encodes a 590-amino acid protein with 95% homology to human and bovine homologs. Northern blot identified GRK5 mRNA of ϳ3, 8, and 10 kilobases with highest expression levels in lung > heart, kidney, colon > thyroid. In functional studies using a normal rat thyroid FRTL5 cells, overexpression of GRK5 by transfecting the plasmid capable of expressing the sense GRK5 RNA suppressed basal cAMP levels and augmented the extent of TSH receptor desensitization, whereas suppression of endogenous GRK5 expression by transfecting the antisense GRK5 construct increased basal cAMP levels and attenuated the extent of receptor desensitization. Although exogenously overexpressed GRK6 also enhanced TSH receptor desensitization, we conclude that GRK5, the predominant GRK isoform in the thyroid, appears to be mainly involved in homologous desensitization of the TSH receptor. Guanine nucleotide-binding regulatory (G)1 protein-coupled receptors transduce a wide variety of extracellular signals (hormones, neurotransmitters, odorants, lights, chemoattractants, etc.) into intracellular signaling events, by activating or inhibiting specific effector enzymes (adenylyl cyclase, phospholipase C, phospholipase A 2 , ion channels, etc.) (1). A rapid loss of responsiveness also occurs following receptor activation by agonist ligand binding in this receptor superfamily. This process is called "homologous desensitization." The mechanisms of homologous desensitization have been extensively studied at the molecular level in rhodopsin and adrenergic receptors (2-4). Newly discovered G protein-coupled receptor kinases (GRKs) and arrestins are involved in this process. GRKs specifically recognize and phosphorylate the agonist-bound form of receptors in the active conformation. Subsequently, arrestin proteins bind exclusively to the phosphorylated and activated receptor, resulting in uncoupling of the receptor and G protein.Six different types of GRKs have so far been cloned and characterized. cDNA for bovine ␤-adrenergic receptor kinase (␤-ARK, now also called GRK2) was first isolated (5), followed by the cloning of cDNAs for bovine ␤-ARK2 (GRK3) (6), bovine rhodopsin kinase (GRK1) (7), human IT11 (GRK4) (8), human GRK5 (9), and human GRK6 (10, 11). Drosophila kinases GPRK-1 and -2 have also been identified (12). These GRKs can be divided into 3 different subgroups according to their homology, cellular localization, and distinct regulatory mechanisms (9, 10). The first subgroup includes GRK4 to 6 and GPRK-1, the second subgroup GRK1, GRK2, and GPRK-2, ...