Temporal asymmetry of sex interconversion in a strain of the homothallic fission yeastSchizosaccharomyces pombe

In the homothallic P/d sex interconversion system in a strain of a fission yeast (Schizosaccharomyces pombe), Pd is apparently twice as frequent as dP. This is interpreted to mean that Pd occurs before DNA replication, whereas dP occurs after. But the probabilities of their occurrence within a cell cycle are about the same (1 in 2⁷ cell divisions).     

Antiplatelet effects of glycoproteins IIb-IIIa antagonist monafram

First Russian glycoprotein (GP) IIb-IIIa antagonist, preparation Monafram, is the F(ab')2 fragment of anti-GP IIb-IIIa monoclonal antibody FRaMon. In in vitro experiments it was shown that Monafram blocked platelet aggregation induced by ADP and thrombin; reduced secretion from platelet granules; and due to simultaneous interaction with two GP IIb-IIIa molecules almost irreversibly bound to platelet surface. Monafram clinical trials were performed in healthy volunteers (n = 10) and in patients with ischemic heart disease undergoing high risk coronary angioplasty (n = 153). Monafram intravenous bolus administration at 0.25 mg/kg decreased ADP-induced platelet aggregation by more than 90, 80, 60 and 30% at 1, 12, 24 and 72 h after injection, respectively. No significant differences were detected between antiaggregatory effects of Monafram and ReoPro introduced at 0.25 mg/kg bolus + 12 h infusion at 0.125 microg/kg per min. Durable inhibition of aggregation after Monafram administration was mediated by platelet-bound preparation--free Monafram was cleared from plasma within 12 h, while platelet-bound preparation occupied more than 90, 70-80 and 40-50% of GP IIb-IIIa at 1, 12-24 and 72 h after injection, respectively. Major bleedings and allergic reactions were detected in none of patients, deep thrombocytopenia--in one patient and antibodies against Monafram--in 5% of patients. Within one month after coronary angioplasty Monafram decreased the number of end points (fatal and nonfatal myocardial infarction and angina recurrence) from 11.4 to 3.3%.     

Stable expression in Chinese hamster ovary cells of a homogeneous recombinant active fragment of human platelet glycoprotein Ibα

A fragment (residues His1-Val289) of the chain of human platelet glycoprotein Ib containing the von Willebrand factor and thrombin binding sites has been expressed in Chinese hamster ovary cells. The secreted soluble recombinant protein had an apparent molecular mass of 42 kD and reacted with a conformation-dependent monoclonal antibody that only binds to native GP Ib, thus demonstrating its proper folding. The rather broad band obtained after immobilization of the recombinant fragment on nitrocellulose could be resolved into a very sharp band of molecular weight of about 35 kD by growing the cells in the presence of tunicamycin, and inhibitor of N-linked glycosylation. The recombinant GP Ib fragments (with or without glycosylation) were purified by immunoaffinity chromatography. Both truncated forms bound vWF in the presence of botrocetin with comparable affinity as a proteolytic 42 kD fragment of purified human platelet GP Ib-IX. They were also retained on thrombin-Sepharose. We then selected a cell clone (B1) that produced over at least three months about 1.5 g of recombinant protein per million cells per day. Using this clone a large-scale production finally yielded milligram amounts of the functionally active recombinant human GP Ib fragment.Abbreviations ABTS 2.2-azino-di-(3-ethylbenzthiazoline sulphonate) - CHO Chinese hamster ovary - dhfr dihydrofolate reductase - GP Ib-IX glycoprotein Ib-IX complex - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - IEF isoelectric focusing - Ig immunoglobulin - mAb monoclonal antibody - MEM minimum essential medium - PMSF phenyl-methylsulfonyl fluoride - SDS sodium dodecyl sulfate - vWF von Willebrand factor     

α2 and β-adrenergic stimulation of corticosterone secretion in rats

Bilateral injection of 6-hydroxydopamine into the medial forebrain bundle (MFB) significantly decreased monoamine concentrations in the hypothalamus. The noradrenaline and serotonin content of the paraventricular nucleus (PVN) was also significantly reduced. These drastic decreases in neurotransmitter concentration did not alter basal secretion of corticosterone. Isoproterenol. a -adrenoceptor agonist (1 mg/kg, i.p.), significantly stimulated corticosterone release in saline and MFB lesioned rats. This stimulation did not differ significantly between the two groups. Clonidine, an ₂-adreceptor agonist, injected either intraperitoneally or intracerebrally just dorsal to the PVN, caused a dose-dependent increase in corticosterone secretion. The stimulation of corticosterone release by clonidine (250 g/kg, i.p.) was antagonised by the selective ₂-adreceptors antagonist, yohimbine (1 mg/kg, i.p.) and significantly reduced by the MFB lesion. These results suggest that corticosterone secretion is stimulated by activation of ₂-adreceptors which occur on noradrenergic nerve terminals in the PVN.     

The pancreatic islets of the teleost Scorpaena scropha

Summary The principal pancreatic islets of the teleost Scorpaena scropha are found ultrastructurally to contain four different kinds of parenchymal cells, viz. ₁-(= D), ₂-, -and agranular cells. The -cells show considerable variations in the shape of the secretory granules. A peculiar feature is that many of these granules are composed of fibrillar subunits, often in parallel arrangement. All -granules are surrounded by membranes and between the membrane and the granule core there is a moderately wide electron lucent space. The electron density of the cytoplasm in the -cells varies somewhat. The ₂-cells possess typical secretory granules with an electron dense core and a closely applied membrane. The secretory granules in the ₁-cells show also a closely applied membrane but a less dense core. Also in the -cells the electron opacity of the cytoplasm varies. The agranular cells are mainly characterized by low cytoplasmic electron density, narrow cisterns of endoplasmic reticulum and sometimes a laminated Golgi complex. Small immature secretory granules are occasionally seen in the cytoplasm of these cells. The significance of the fibrillar -granules remains obscure.This work was supported by grants from the Nordic Insulin Fund, the Town of Umeå, the Swedish Medical Research Council (Project No. B69-12X-718-04A), and by a postdoctoral fellowship from the United States Public Health Service.     

Localization of adhesive proteins in two newly subdivided zones in electron-lucent matrix of human platelet α-granules

Summary Platelet -granules have been reported to consist of two zones, nucleoid and electron-lucent matrix, with different densities under electron microscopy. When washed human platelets were prepared by a rapid freeze-substitution method using liquid helium, we found that the electron-lucent matrix could be further subclassified into two zones having different densities: the intermediate and the light zones. The light zone was located at the periphery opposite the most dense nucleoid and contained several tubular structures with diameters of about 20 nm. The intermediate zone often laid between the nucleoid and light zone. By careful inspection, intermediate and light zones could even be identified in the platelets embedded in Lowicryl K4M, which where then used to localize several adhesive proteins in these two zone by immunocytochemical studies using the respective polyclonal antibodies. Fibrinogen, thrombospondin, and fibronectin were detected only in the intermediate zone. In contrast, von Willebrant factor (vWF) was localized only in the light zone, suggesting an association between vWF and the tubular structures in the light zone. In the nucleoid, none of these adhesive proteins were detected. Glycoprotein IIb/IIIa, a receptor for these adhesive proteins on the platelet surface, was detected not only on the outer surface of the cell membranes but also on the inner surface of the -granule membrane. These data indicate that two zones with different densities in electron-lucent matrix and functions exist in the platelet -granules.     

Design and synthesis of thrombin inhibitors

Summary As part of our programme directed at the development of enzyme inhibitors based on transition-state mimics, we discovered in the early 1980s that P3-P3 fragments of human fibrinogen A, containing the ketomethylene isostere Arg--[COCH₂]Gly at P1-P1, were potent inhibitors of thrombin. Such low-molecular-weight inhibitors are expected to be clinically useful as anticoagultant drugs. In our more recent investigations, the P1-P1 moiety has been replaced with various arginine or lysine ketones. The resulting compounds showed the following order of thrombin inhibitory potency: -ketoesters > fluoroketones >alkoxymethylketones > difluoro--ketoamides >-ketoesters >alkyl ketones. In contrast to all other lysine/arginine pairs studied previously, the inhibitor based on a lysine -ketoester proved superior to the corresponding arginine analogue. A possible explanation for this finding is discussed. All the highly electrophilic ketones (e.g., fluoroketones) were found to exhibit slow-binding kinetics with thrombin, which is likely to be a disadvantage in clinical use. Alkoxymethyl ketones were devoid of such behaviour and have been developed further to yield nanomolar inhibitors of low molecular weight and good selectivity for thrombin. One of these ketones was found to compare favourably with known thrombin inhibitors in anticoagulant assays. The synthesis of various types of inhibitor mentioned above is described, together with structure-activity correlations for inhibition of thrombin.     

Über das Inselorgan des Axolotl (Siredon mexicanum)

Zusammenfassung Das Inselorgan des Axolotl (Siredon mexicanum) enthält drei Zelltypen mit verschiedener spezifischer Granulation: 1. A-Zellen mit elektronendichten, dichtgepackten, kugeligen -Granula, 2. B-Zellen mit -Granula, die meist kristallinen Inhalt haben, 3. D-Zellen, die ähnliche Granula wie die A-Zellen aufweisen, doch durch ihre geringere Größe, Elektronendichte und Verteilung als eigener Zelltyp abgegrenzt werden können. Außerdem werden lysosomenartige Gebilde und Microtubuli beobachtet. Die periodische Struktur der Kristalle in den -Granula wird beschrieben. Die Kristallform des Insulinsulfats und Zink-Insulins wird im Zusammenhang mit dem polymorphen Bild der -Granula diskutiert.

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Summary The pancreatic islets of the Axolotl (Siredon mexicanum) contain three types of cells with specific granulation: 1. A-cells are densly packed with ovoid electrondense -granules, 2. B-cells with -granules, which contain very often crystalline inclusions. 3. D-cells show structural similarities to the A-cells, but are distinguished according to the smaller size, lesser electrondensity, and distribution of their granules as a cell type of its own. In all three cell types lysosomal bodies and microtubules are seen. The periodic structure of the crystals in -granules is described. Their possible relationship to sulfated-insulin and zinc-insulin is discussed.

     

Recruitment of beta-2-glycoprotein 1 to cell surfaces in extrinsic and intrinsic apoptosis

Apoptotic cells and phagocytes have developed a diverse array of distinct ligand-receptor systems that drive the recognition and uptake of dying cells. Phagocytes recognize apoptotic cells either directly, by binding to specific ligands at their cell surface, or indirectly, by binding to bridging proteins that bind these ligands. Previous observations showed that the plasma bridging protein 2GP1, binds PS containing vesicles, and enhances their binding and engulfment by phagocytes in vitro. In this study we show that apoptotic cells injected intravenously and intraperitonealy into syngeneic mice recruited the PS binding protein, 2GP1. Examination of peritoneal exudates and spleen thin sections showed that only the injected apoptotic cells picked up endogenous 2GP1. Recovery of cells from the peritoneum showed that apoptotic cells bearing 2GP1 were clustered around host peritoneal phagocytes. In addition, tissue sections from mice injected with Fas antibody showed colocalization of 2GP1 with TUNEL-positive apoptotic cells. These results provide evidence that endogenous 2GP1 binds apoptotic cells in vivo, suggesting that the protein plays an important physiologic role in the recognition of dying cells.     

Effect of shape, size, and valency of multivalent mannosides on their binding properties to phytohemagglutinins

Clusters of di-, tri-, and tetra-antennary -D-mannopyranosides were synthesized in good yields based on the coupling of amine-bearing mono- or trisaccharide {Man (16)[Man (13)]Man} haptens to poly-isocyanate or -isothiocyanate tethering cores. The relative binding properties of the resulting multivalent ligands were determined by turbidimetric and solid phase enzyme-linked lectin assays (ELLA) using plant lectins (phytohemagglutinins) Concanavalin A (Con A) and Pisum sativum (pea lectin) having four and two carbohydrate binding sites, respectively. Rapid and efficient cross-linking between tetravalent Con A and mannopyranosylated clusters were measured by a microtiter plate version of turbidimetric analyses. In inhibition of binding of the lectins to yeast mannan, the best tetravalent monosaccharide (30) and trisaccharide (31) inhibitors were shown to be 140 and 1155 times more potent inhibitors than monomeric methyl -D-mannopyranoside against pea lectin and Con A, respectively. Compounds 30 and 31 were thus 35 and 289 fold more potent than the reference monosaccharide based on their hapten contents. As a general observation, the ligands bearing the Man (16)[Man (13)]Man trimannoside structures were found to be more potent inhibitors for Con A than the ligands having single mannoside residues, whereas pea lectin could not discriminate between the two types of ligands.     

Modelling endplate currents: dependence on quantum secretion probability and decay of miniature current

Quantification of the time course and amplitude of endplate currents (EPC) was made with respect to dispersion of quanta secretion and to changes in the exponential decay of miniature endplate currents (_mepc). The relationship between RPC amplitude and _mepc follows a double-exponential curve with ₁= 0.3 ms and ₂ = 6 ms. If the amplitude of fully synchronised EPC is taken as 100%, then the loss of EPC amplitude is already 42% with physiological parameters of dispersion (the half-rise and decay constant of distribution of secretion probability = 0.5 ms, _mepc =1 ms). This loss is even more substantial if secretion is more dispersed or miniature endplate currents decay faster. Correspondence to: F. Vyskocil     

Interaction of thrombin with antithrombin, heparin cofactor II, and protein C inhibitor

-Thrombin is a trypsin-like serine proteinase involved in blood coagulation and wound repair processes. Thrombin interacts with many macromolecular substrates, cofactors, cell-surface receptors, and blood plasma inhibitors. The three-dimensional structure of human -thrombin shows multiple surface exosites for interactions with these macromolecules. We used these coordinates to probe the interaction of thrombin's active site and two exosites, anion-binding exosite-I and -II, with the blood plasma serine proteinase inhibitors (serpins) antithrombin (AT), heparin cofactor II (HC), and protein C inhibitor (PCI). Heparin, a widely used anticoagulant drug, accelerates the rate of thrombin inhibition by AT, PCI, and HC. Thrombin Quick II is a dysfunctional thrombin mutant with a Gly 226 Val substitution in the substrate specificity pocket. We found that thrombin Quick II was inhibited by HC, but not by AT or PCI. Molecular modeling studies suggest that the larger Val side chain protrudes into the specificity pocket, allowing room for the smaller P1 side chain of HC (Leu) but not the larger P1 side chain of AT and PCI (both with Arg). _T ^–-Thrombin and thrombin Quick I (Arg 67 Cys) are both altered in anion-binding exosite-I, yet bind to heparin-Sepharose and can be inhibited by AT, HC, and PCI in an essentially normal manner in the absence of heparin. In the presence of heparin, inhibition of these altered thrombins by HC is greatly reduced compared to both AT and PCI. -Thrombin with chemically modified lysines in both anion-binding exosite-I and -II has no heparin accelerated thrombin inhibition by either AT or HC. Thrombin lysine-modified in the presence of heparin has protected residues in anion-binding exosite-II and the loss of heparin-accelerated inhibition by HC is greater than that by AT. Collectively, these results suggest differences in serpin reactive site recognition by thrombin and a more complicated mechanism for heparin-accelerated inhibition by HC compared to either AT or PCI.Abbreviations used: AT, antithrombin; HC, heparin cofactor II; PCI, protein C inhibitor; serpin(s), serine proteinase inhibitor(s); FPRck, D-Phe-Pro-Arg-chloromethyl ketone; FPLck, D-Phe-Pro-Leu-chloromethyl ketone; HEPES, (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid); SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; HNP, 20mM HEPES, 150mM NaCl, 0.1% (w/v) poly(ethyleneglycol) (M_r = 8000) buffer atpH 7.4; Unp-PLPT, unprotected pyridoxal 5phosphate modified-thrombin; HPPLPT, heparin-protected pyridoxal 5phosphate modifiedthrombin.     

Phosphoinositide-generated messengers in cardiac signal transduction

A multitude of agonists like e.g. endothelin-I, angiotensin-II, serotonin, thrombin, histamine and vasopressin as well as ₁-adrenergic and muscarinic stimulation lead to stimulation of the phosphoinositide cycle in the heart. Besides this seven membrane spanning-domain receptor-coupled stimulation of the key enzyme of the phosphoinositide cycle, phospholipase C-, another class of hormones, growth factors, also couple to the phosphoinositide cycle, now through receptors with intrinsic tyrosine kinase activity that can phosphorylate and stimulate the phospholipase C- isozyme. In this review we summarize the multitude of receptor (sub)types, G-protein-subunit- and phospholipase C-isozymes that are present in the heart. Furthermore, generation of second messengers and cellular responses are described together with the (patho)physiological implications for the heart of phosphoinositide cycle activation and second messenger accumulation.     

Immunocytochemical evidence for the translocation of α-granule membrane glycoprotein IIb/IIIa (integrin αIIbβ3) of human platelets to the surface membrane during the release reaction

Summary The localization of glycoprotein (GP) IIb/IIIa (integrin _IIb3) in both resting and thrombin-activated platelets was studied immunocytochemically. By the pre-embedding method where only the GP IIb/IIIa molecules on the surface of platelets were immunostained, the distribution of protein A-colloidal gold label was randomly distributed along the surface membrane of resting platelets at a density of 18.0±2.7 gold particles/m of membrane. At 15 s after stimulation by 0.1 U/ml of thrombin in an unstirred platelet suspension, the spheroid-shaped platelets with pseudopodia still had normal numbers of -granules, and the density of gold particles was 19.7±3.6 particles/m. At 5 min, the -granules were no longer present because of the release reaction, and the density of gold particles significantly increased (27.0±3.7 particles/m; p<0.01). In immunostained ultra-thin frozen sections, the gold particles were detected not only on the surface membrane, including the open canalicular system (OCS), but also on the -granule membranes of resting platelets. At 30 s after thrombin stimulation the -granules fused with the OCS, resulting in the formation of a swollen OCS, which still had gold particles on its membrane. At 5 min, the gold particles were detected on the membrane of the swollen OCS located near the surface membrane, while very few gold particles were present on the membrane of the OCS in the central part of the platelets. These results demonstrate that -granule membrane GPIIb/IIIa translocates to the surface membrane through the membrane of the OCS. Also the translocation of -granule membrane GPIIb/IIIa gives rise to an actual increase in GPIIb/IIIa on the surface membrane during the release reaction induced by thrombin.     

Effects of Biogenic Amines and Polypeptide Hormones on Protein Kinase A and Adenylyl Cyclase Activities in Muscles of the Mollusc Anodonta cygnea

The effects of biogenic amines, glucagon, and insulin on the cAMP-dependent protein kinase A (PKA) activity have been studied in the muscle tissue of the freshwater bivalve mollusc Anodonta cygnea. It was shown that serotonin, glucagon, and insulin both in vivo and in vitro stimulated PKA activity, whereas isoproterenol inhibited it. The stimulating effect of serotonin and inhibiting effect of isoproterenol was blocked by serotoninergic (cyproheptadine) and adrenergic (propranolol) inhibitors, which confirms specificity of the effect of biogenic amines on the PKA activity. Taking into account participation of adenylyl cyclase system in action of the above hormones, the revealed hormonal effects on the PKA activity produce metabolic effects via the following chain reaction. In the case of serotonin and glucagon: receptor G_s-protein AC cAMP PKA phosphorylation of glycogen synthase (GS) and glucose-6-phosphate dehydrogenase (G6PDH) and inhibition of their activity; in the case of isoproterenol: -adrenoreceptor G_i-protein AC inhibition decreasing PKA inhibition of phosphorylase and stimulation of GSI and G6PDH. A participation is suggested of the insulin-stimulated AC signaling system in the mechanism of the mitogenic insulin effect mediated, as shown in this work, via the PKA activation, but not of the metabolic effect of insulin.     

Calcium oscillation and phosphatidylinositol 3-kinase positively regulate integrin α<Subscript>IIb</Subscript>β<Subscript>3</Subscript>-mediated outside-in signaling

Summary The frequency of calcium oscillation reveals the platelet activation status, however, the biological significance of the periodic calcium responses and methods of communication with other integrin-mediated signals are not clear. RGD-containing disintegrin rhodostomin coated substrates were employed to enhance platelet spreading and calcium oscillation through direct binding and clustering of the receptor integrin _IIb3. The results showed that the activation of phosphatidylinositol 3-kinase (PI3-K) and internal calcium pathways were crucial for _IIb3 outside-in signaling. PI3-K antagonists wortmannin and LY294002 inhibited disintegrin substrates and induced platelet spreading and calcium oscillation. At the same time, pretreatment of platelets with the microsomal calcium–ATPase inhibitor thapsigargin to deplete internal calcium stores severely impaired the calcium oscillation as well as PI3-K activation and spreading on disintegrin substrates. Because inhibition of one pathway could inhibit the other, our data indicates that PI3-K and calcium oscillation are synergistically operated and form a positive-feedback regulation in integrin _IIb3-mediated outside-in signaling.     

A lyophilized aqueous extract of<Emphasis Type="Italic"> Maytenus ilicifolia</Emphasis> leaves inhibits histamine-mediated acid secretion in isolated frog gastric mucosa

Lyophilized aqueous extract of Maytenus ilicifolia leaves (LAEMIL) is commonly used in Brazilian folk medicine in the treatment of dyspepsia as well as gastric ulcers. We have investigated the effect and the possible mechanism of action of the LAEMIL on acid secretion in isolated frog gastric mucosa incubated in an Ussing chamber. It was observed that LAEMIL (7–28 mg%) as well as cimetidine (125–4,000 M), a well-known histamine H₂ receptor antagonist, decreased basal acid secretion in a concentration-dependent manner. Similarly to cimetidine (190 M), LAEMIL (21 mg%) also inhibited gastric acid secretion induced by increasing concentrations of histamine (50–800 M). The EC₅₀ values for histamine alone and histamine in the presence of LAEMIL or cimetidine were 94.6 M (71.1–125.9 M), 244.9 M (209.4–286.4 M) and 142.2 M (23.6–855.0 M), respectively. LAEMIL, histamine and cimetidine were effective on acid secretion only when added to the serosal surface of the mucosa. Furthermore, simultaneous addition of LAEMIL and cimetidine at concentrations, per se, ineffective, caused a 16% reduction in the basal acid secretion [from 8.3±0.3 to 6.9±0.2 Eq g^–1 (15 min)^–1, n=4]. Although effects such as inhibition of histamine biosynthesis and/or histamine release can not be ruled out, our data suggest that LAEMIL, like cimetidine, reduces acid secretion in the isolated frog gastric mucosa by antagonising histamine H₂ receptors.Abbreviations LAEMIL Lyophilized aqueous extract of Maytenus ilicifolia leaves - Hist Histamine - Cim Cimetidine     

Inward rectifier K channels in renal epithelioid cells (MDCK) activated by serotonin

Summary The present study has been performed to test for the effect of intracellular calcium and of serotonin on the channel activity in patches from subconfluent MDCK-cells. In inside-out patches, inwardly rectifying potassium-selective channels are observed with open probabilities of 0.01±0.01, 0.24±0.03 and 0.39±0.07, at 100 nmol/liter, 1 mol/liter or 10 mol/liter calcium activity, respectively. The single-channel slope conductance is 34±2 pS, if the potential difference across the patch (V ) is zero, and approaches 59±1 pS, ifV is –50 mV, cell negative. In the cell-attached mode, little channel activity is observed prior to application of serotonin (open probability=0.03±0.03). If 1 mol/liter serotonin is added to the bath perfusate, the open probability increases rapidly to a peak value of 0.34±0.04 within 8 sec. In continued presence of the hormone, the open probability declines to approach 0.06±0.02 within 30 sec. At zero potential difference between pipette and reference in the bath (i.e., the potential difference across the patch is equal to the potential difference across the cell membrane), the single-channel conductance is 59±4 pS. In conclusion, inwardly rectifying potassium channels have been identified in the cell membrane of subconfluent MDCK-cells, which are activated to a similar extent by increase of intracellular calcium activity to 1 mol/liter and by extracellular application of 1 mol/liter serotonin.     

Noradrenalin antagonizes effects of serotonin and acetylcholine in the seawater eel intestine

After inhibiting ion and water transport with 10^-6 mol·l^-1 serotonin and 10^-6 mol·l^-1 methacholine, a muscarinic agonist of acetylcholine, 10^-5 mol·l^-1 (±)noradrenaline restored the serosa-negative transepithelial potential difference and short-circuit current in a step-like manner, accompanied by an increase in water absorption across the seawater eel intestine. Such recovery by noradrenalin was not obtained after pretreatment with 10^-7 mol·l^-1 eel atrial natriuretic peptide. This means that the inhibitory mechanisms of serotonin and acetylcholine are different from those of atrial natriuretic peptide. Similarly, 10^-7 mol·l^-1 clonidine and guanabenz (₂-agonists) also reversed the inhibitory action of serotonin and methacholine, but 10^-7 mol·l^-1 phenylephrine (₁-agonists) and 10^-7 mol·l^-1 isoproterenol (-agonist) did not antagonize serotonin and methacholine actions. Further, the enhancement by 10^-5 mol·l^-1 noradrenalin was blocked by 10^-4 mol·l^-1 yohimbine (₂-agonists) and 10^-4 mol·l^-1 prazosin (₁-agonists), but not by 10^-4 mol·l^-1 propranolol (-antagonist). Although relatively high dosage is required to obtain a significant effect, and discrimination between ₁- and ₂- is not successful in the present study, these results suggest that noradrenalin acts on an -type receptor. The -type receptor may exist on the enterocytes, since the effects of noradrenalin are observed even in the presence of 10^-6 mol·l^-1 tetrodotoxin. Interestingly, the tissue resistance also increased in parallel with increase in the short-circuit current after treatment with noradrenalin in the posterior part of the seawater eel intestine.Abbreviations ACh acetylcholine - 5-HT serotonin - eANP eel atrial natriuretic peptide - I _sc short-circuit current - MCh methacholine - NA noradrenalin - PD transepithelial potential difference - R _t tissue resistance - TTX tetrodotoxin - VIP vasoactive intestinal peptide