Bradykinin dilates rat middle cerebral artery and its large branches via endothelial B2 receptors and release of nitric oxide

Ring segments of rat middle cerebral artery (MCA) were prepared for measurement of isometric force and precontracted with 10⁻⁴ M uridine triphosphate (UTP). Concentration-effect curves (CEC) were constructed for bradykinin (BK, 10⁻⁸–10⁻⁵ M) in segments with functionally intect (E+) or denuded (E−) endothelium. E− segments did not dilate to BK. The BK receptor was characterized by application of specific B₁ or B₂ antagonists [des-Arg⁹-Leu⁸] BK (10⁻⁵ M) and [ -Arg⁰-Hyp³-Thi⁵- -Tic⁷-Oic⁸] BK (HOE140,3 × 10⁻⁷ M), respectively, or B₁ agonist [des-Arg⁹] BK (10⁻⁸–10⁻⁴ M). Involvement of nitric oxide (NO) was tested with N^G-nitro- -arginine (LNNA, 10⁻⁴ M). BK induced concentration-dependent relaxation with a maximal effect (E_max) of 40.86 ± 1.50% at 10⁻⁶ M and a pD₂ (−log₁₀ EC₅₀) of 6.818 ± 0.044. This relaxation could be prevented with HOE140 or LNNA, but was not influenced by [des-Arg⁹-Leu⁸] BK. [des-Arg⁹] BK did not induce any effect. These results demonstrate that BK induced relaxation via endothelial B₂ receptors and release of NO in isolated rat MCA.     

Bradykinin counteracts the stimulatory effect of angiotensin-(1-7) on the proximal tubule Na+ -ATPase activity through B2 receptor

Recently, we demonstrated that angiotensin-(1–7) (Ang-(1–7)) stimulates the Na⁺-ATPase activity through a losartan-sensitive angiotensin receptor, whereas bradykinin inhibits the enzyme activity through the B₂ receptor [Regul. Pept. 91 (2000) 45; Pharmacol. Rev. 32 (1980) 1]. In the present paper, the effect of bradykinin (BK) on Ang-(1–7)-stimulated Na⁺-ATPase activity was evaluated. Preincubation of Na⁺-ATPase with 10⁻⁹ M Ang-(1–7) increases enzyme activity from 7.9±0.9 to 14.1±1.5 nmol Pi mg⁻¹ min⁻¹, corresponding to an increase of 79% (p<0.05). This effect is reverted by bradykinin in a dose-dependent manner (10⁻¹⁴–10⁻⁸ M), reaching maximal inhibitory effect at 10⁻⁹ M. Des-Arg⁹ bradykinin (DABK), an agonist of B₁ receptor, at the concentrations of 10⁻⁹–10⁻⁷ M, does not mimic the BK inhibitory effect, and des-Arg⁹-[Leu⁸]-BK (DALBK), a B₁ receptor antagonist, at the concentrations of 10⁻¹⁰–10⁻⁷ M, does not prevent the inhibitory effect of BK on Ang-(1–7)-stimulated enzyme. On the other hand, HOE 140, an antagonist of B₂ receptor, abolishes the inhibitory effect of BK on the Ang-(1–7)-stimulated enzyme in a dose-dependent manner, reaching maximal effect at 10⁻⁷ M. Taken together, these data indicate that stimulation of B₂ receptors by BK can counteract the stimulatory effect of Ang-(1–7) on the proximal tubule Na⁺-ATPase activity.     

Structure-activity relationships of trout bradykinin ([Arg(0),Trp(5),Leu(8)]-bradykinin)

Trout bradykinin ([Arg⁰,Trp⁵,Leu⁸]-BK) produces sustained and concentration–dependent contractions of isolated longitudinal smooth muscle from trout stomach, although mammalian BK is without effect. Circular dichroism studies have demonstrated that trout BK, unlike mammalian BK, does not adopt a stable β-turn conformation, even in the presence of sodium dodecyl sulfate (SDS) or trifluoroethanol. The myotropic actions of a series of analogs in which each amino acid in trout BK was replaced by either alanine or the corresponding D-isomer were investigated. The peptides with Ala⁴, D-Pro³, D-Trp⁵, D-Ser⁶, and D-Pro⁷ substitutions were inactive and did not act as antagonists of trout BK. The analog with [Ala⁵] was a weak partial agonist. The substitution (Arg⁰ → Ala) led to >50-fold decrease in potency but, in contrast to the importance of Phe⁸ in both BK and desArg⁹-BK in activating the mammalian B₂ and B₁ receptors respectively, substitutions at Leu⁸ in trout BK had only a minor effect on potency. Antagonists to the mammalian B₂ receptor generally contain a D-aromatic amino acid at position 7 of BK but the analog [Arg⁰,Trp⁵,D-Phe⁷,Leu⁸]-BK was a weak agonist at the trout receptor. Similarly, the potent nonpeptide mammalian B₂ receptor antagonist FR173657 was without effect on the action of trout BK. These data suggest the hypothesis that the receptor binding conformation of trout BK is defined by the central region (residues 3–7) of the peptide but is adopted only upon interaction with the receptor. The bioactive conformation is probably stabilized by an ionic interaction between Arg⁰ in the peptide and an acidic residue in the receptor.     

Interaction of ovokinin(2-7) with vascular bradykinin 2 receptors

Intravenous administration of ovokinin(2–7), a cleavage peptide derived from ovalbumin, dose-dependently (0.1–5 mg/kg) lowered the mean arterial pressure (MAP) that was not accompanied by a significant change in the heart rate (HR) of urethane-anesthetized rats. The hypotensive effects of ovokinin(2–7) were five orders of magnitude lower compared to that of bradykinin and were largely prevented by pretreatment with the bradykinin B₂ receptor antagonist HOE140 (81.6±18.4%) and moderately affected by the B₁ receptor antagonist [des-Arg¹⁰]-HOE140 (26.3±15.5%). Intracellular Ca²⁺ levels, as measured by Fur 2-AM, were significantly elevated in cultured aorta smooth muscle cells by ovokinin(2–7). The increases were abolished by HOE140 and unaffected by [des-Arg¹⁰]-HOE140. The elevation of intracellular Ca²⁺ by ovokinin(2–7) was dependent on Ca²⁺ entry from extracellular space as it was reduced in a Ca²⁺-free solution. Pretreatment of the cells with the phospholipase C inhibitor U73122 (2 μM) eliminated the Ca²⁺ increase by the peptide. PA phosphohydrolase and phospholipase A₂ inhibitors significantly reduced the responses as well. Our results show that ovokinin(2–7) modulates cardiovascular activity by interacting with B₂ bradykinin receptors.     

Hydrodynamic properties of the fractions of mannan formed by Rhodotorula rubra yeast

Aqueous solutions of fractions of an extracellular linear mannan formed by Rhodotorula rubra yeast have been investigated by hydrodynamic methods (high-speed sedimentation, translation isothermic diffusion and viscometry). The molecular weight was determined according to Svedberg ( ) and the polydispersity parameters of the initial sample were also determined (M_w/M_n = 1·20 and M_z/M_w = 1·21). Relationships between the molecular weight (M) and s_o, D_o and [η] in the range were: [η] = 2·33 × 10⁻² M^0.75, D_o = 1·65 × 10⁻⁴ M^0·58, s_o = 2·24 × 10⁻¹⁵ M^0·43. The equilibrium rigidity and hydrodynamic diameter of chains representing mannan molecules were evaluated.     

Leukotriene D4 induced calcium changes in U937 cells may utilize mechanisms additional to inositol phosphate production that are pertussis toxin insensitive but are blocked by phorbol myristate acetate

DMSO differentiated U937 cells responded to 10⁻⁶ M LTD₄, LTB₄ and FMLP with an increase in both InsP formation and [Ca²⁺]_i. FMLP caused a greater rise in InsPs than either LTD₄ or LTB₄, which were equivalent. LTD₄, however, caused a greater increase in [Ca²⁺]_i than LTB₄ (4-fold) or FMLP. The FMLP [Ca²⁺]_i and InsP responses were abolished by pertussis toxin (100 ng/ml for 4 h) but were unaffected by PMA (10⁻⁷ M for 3 min). In contrast, the LTD₄ [Ca²⁺]_i and InsP responses were reduced by only 50% by pertussis toxin, whilst PMA reduced the [Ca²⁺]_i and InsP responses to LTD₄ by 75 and 30%, respectively. These results suggest that mechanisms additional to InsP formation exist for mediating LTD₄ evoked increases in [Ca²⁺]_i.     

Kinetics and mechanism of the stoichiometric oxygenation of [Cu(fla)(idpa)]ClO4 [fla=flavonolate, IDPA=3,3′-imino-bis(N,N-dimethylpropylamine)] and the [Cu(fla)(idpa)]ClO4-catalysed oxygenation of flavonol

Oxygenation of [Cu^II(fla)(idpa)]ClO₄ (fla=flavonolate; IDPA=3,3′-iminobis(N,N-dimethylpropylamine)) in dimethylformamide gives [Cu^II(idpa)(O-bs)]ClO₄ (O-bs=O-benzoylsalicylate) and CO. The oxygenolysis of [Cu^II(fla)(idpa)]ClO₄ in DMF was followed by electronic spectroscopy and the rate law −d[{Cu^II(fla)(idpa)}ClO₄]/dt=k_obs[{Cu^II(fla)(idpa)}ClO₄][O₂] was obtained. The rate constant, activation enthalpy and entropy at 373 K are k_obs=6.13±0.16×10⁻³ M⁻¹ s⁻¹, ΔH^‡=64±5 kJ mol⁻¹, ΔS^‡=−120±13 J mol⁻¹ K⁻¹, respectively. The reaction fits a Hammett linear free energy relationship and a higher electron density on copper gives faster oxygenation rates. The complex [Cu^II(fla)(idpa)]ClO₄ has also been found to be a selective catalyst for the oxygenation of flavonol to the corresponding O-benzoylsalicylic acid and CO. The kinetics of the oxygenolysis in DMF was followed by electronic spectroscopy and the following rate law was obtained: −d[flaH]/dt=k_obs[{Cu^II(fla)(idpa)}ClO₄][O₂]. The rate constant, activation enthalpy and entropy at 403 K are k_obs=4.22±0.15×10⁻² M⁻¹ s⁻¹, ΔH^‡=71±6 kJ mol⁻¹, ΔS^‡=−97±15 J mol⁻¹ K⁻¹, respectively.     

The versatile coordination chemistry of tricyanoethenolate, [(NC)2C=C(CN)O]

The reaction of meso-tetrakis (4-dimethoxyphenyl) porphinatomanganese(II), MnTP_OMeP, with TCNE (TCNE = tetracyanoethylene) leads to the formation of [MnTP_OMeP]⁺ [TCNE]⁻ and [MnTP_OMeP]⁺[OC(CN)C(CN)₂]⁻. The single-crystal X-ray structures of the latter as well as [Cu(bipy)₂Cl]⁺ [OC(CN)C(CN)₂]⁻ were determined. The former has a disordered [OC(CN)C(CN)₂]⁻ bridging via C and O between a pair of Mn^III sites, whereas the latter has an isolated [OC(CN)C(CN)₂]⁻ unbound to Cu^II. The IR characterization for μ₂-C,O bound [OC(CN)C(CN)₂]⁻ is at 2219m and 2196s (νCN) cm⁻¹ and at 1558s (νCO) cm⁻¹ while for unbound [OC(CN)C(CN)₂]⁻ it is at 2210m, 2203m, 2181m (νCN) cm⁻¹ and at 1583s (νCO) cm⁻¹.     

Toxicity and mutagenicity of X-rays and [125I]dUrd or [3H]TdR incorporated in the DNA of human lymphoblast cells

We measured the toxicity and mutagenicity induced in human diploid lymphoblasts by various radiation doses of X-rays and two internal emitters. [¹²⁵I]iododeoxyuridine ([¹²⁵I]dUrd) and [³H]thymidine ([³H]TdR), incorporated into cellular DNA. [¹²⁵I]dUrd was more effective than [³H]TdR at killing cells and producing mutations to 6-thioguanine resistance (6TG^R). No ouabain-resistant mutants were induced by any of these agents. Expressing dose as total disintegrations per cell (dpc), the D₀ for cell killing for [¹²⁵I]dUrd was 28 dpc and for [³H]TdR was 385 dpc. The D₀ for X-rays was 48 rad at 37°C. The slopes of the mutation curves were approximately 75 × 10⁻⁸ 6TG^R mutants per cell per disintegration for [¹²⁵I]dUrd and 2 × 10⁻⁸ for [³H]TdR. X-Rays induced 8 × 10⁻⁸ 6TG^R mutants per cell per rad. Normalizing for survival, [¹²⁵I]dUrd remained much more mutagenic at low doses (high survival levels) than the other two agents. Treatment of the cells at either 37°C or while frozen at −70°C yielded no difference in cytotoxicity or mutation for [¹²⁵I]dUrd or [³H]TdR, whereas X-rays were 6 times less effective in killing cells at −70°C.

Assuming that incorporation was random throughout the genome, the mutagenic efficiencies of the radionuclides could be calculated by dividing the mutation rate by the level of incorporation. If the effective target size of the 6TG^R locus is 1000–3000 base pairs, then the mutagenic efficiency of [¹²⁵I]dUrd is 1.0–3.0 and of [³H]TdR is 0.02–0.06 total genomic mutations per cell per disintegration. ¹²⁵I disintegrations are known to produce localized DNA double-strand breaks. If these breaks are potentially lethal lesions, they must be repaired, since the mean lethal dose (D₀) was 28 dpc. The observations that a single dpc has a high probability of producing a mutation (mutagenic efficiency 1.0–3.0) would suggest, however, that this repair is extremely error-prone. If the breaks need not be repaired to permit survival, then lethal lesions are a subset of or are completely different from mutagenic lesions.     

Properties of amino-terminal parathyroid hormone-related peptides modified at positions 11–13

Biological properties of amino-terminal PTHrP analogues modified in the region 11–13 were examined using ROS 17/2.8 cells. [Leu¹¹,D-Trp¹²,Arg¹³,Tyr³⁶]PTHrP(1–36)amide had a 17-fold lower binding affinity for the receptor (apparent K_d: 5 × 10⁻⁸ M) than [Tyr³⁶]PTHrP(1–36)amide or [Arg^11,13,Tyr³⁶]PTHrP(1–36)amide (apparent K_d for both: 2 × 10⁻⁹ M). Moreover, it is only a weak partial agonist despite completely inhibiting radioligand binding. [Leu¹¹,D-Trp¹²,Arg¹³,Tyr³⁶,Cys³⁸]PTHrP(7–38) and PTHrP(7–34)amide had similar receptor affinities (apparent K_ds: 5 × 10⁻⁸ M and 8 × 10⁻⁸ M), while that of [Nle^8,18,Tyr³⁴]bPTH(7–34)amide was more than 10-fold lower (apparent K_d: 2 × 10⁻⁶ M). These changes in biological properties suggest that high affinity receptor binding requires both amino- and carboxyl-terminal domains of the PTHrP(1–36) sequence and/or intramolecular interactions which are impaired by the D-Trp substitution for Gly¹².     

Characterization of the B2 receptor and activity of bradykinin analogs in SHP-77 cell line by Cytosensor microphysiometer

The Cytosensor microphysiometer device (Molecular Devices, Sunnyvale, CA) is capable of measuring the rate at which cells acidify their environment in response to ligand–receptor binding. By measuring the extracellular acidification response (ECAR) we characterized some aspects of ligand–B₂ receptor interaction in SHP-77 cell line. SHP-77 cells maximally acidified their environment within 30 s after the exposure to bradykinin (BK) or the BK agonist, B9972, with the maximum effect seen at a ligands concentration of 1 μM. Fetal bovine serum (FBS) modulated the binding of BK or B9972, showing that B9972 is a partial agonist. In addition, the binding of BK agonist or antagonist to the B₂ receptor showed different ECAR and different interaction with other intracellular and plasma membrane proteins. Our microphysiometrical results showed that two parameters, antagonist binding affinity (pD₂) and antagonist potency (pIC₅₀) are required to characterize BK antagonist activity for the B₂ receptor in the SHP-77 cell line. The previously used parameter of B₂ antagonist activity, pA₂, had high variation and poor correlation with the inhibition of SHP-77 cell growth in vitro and suppression of tumor growth when SHP-77 cells were injected to mice. Our results permit us to conclude that BK agonists and antagonists differ in their interactions with the B₂ receptor and consequently elicit different cell responses. Based on our results, we have developed a new microphysiometrical assay for analyzing the activity of BK agonists and antagonist in SHP-77 cells, which may facilitate the discovery of new potent anticancer drugs.     

Acetyl glyceryl ether phosphorylcholine (platelet-activating factor) mediates heightened metabolic activity in macrophages: Studies on PGE, TXB2 and O2 production, spreading, and the influence of calmodulin-inhibitor W-7

The phospholipid mediator AGEPC (acetyl glyceryl ether phosphorylcholine) was examined for its effects on guinea pig peritoneal macrophages. At a concentration of 10⁻⁹ -10⁻⁶ M, AGEPC evoked release of prostaglandin E (PGE) and thromboxane B₂ (TXB₂) from albumin-elicited macrophages. It also triggerd generation of O⁻₂ by Corynebacterium parvum-induced cells. Moreover, it caused augmented spreading of macrophages. The calmodulin antagonis W-7 attenuated AGEPC-mediated O⁻₂ production and cell spreading whereas prostanoid synthesis was enhanced. These novel actions of AGEPC on the major cellular component of the inflammatory process attest to its role as a potent mediator of immunoinflammatory responses.     

Syntheses, structures and magnetic properties of mono- and di-manganese inclusion compounds

Mono- and di-manganese inclusion compounds 1 and 2 are reported. Two mono-manganese molecules Mn(bpy)₂(NO₃)₂ (bpy=2,2′-bipyridine) and [Mn(bpy)₂(NO₃)(H₂O)]·NO₃ coexist in the mole ratio of 1:1 in the structure of 1, while two di-manganese molecules [Mn₂O(bpy)₂(phtha)₂(H₂O)₂]·(NO₃)₂ (phtha=phthalate) and [Mn₂O(bpy)₂(phtha)₂(NO₃)(H₂O)]·NO₃ in the structure of 2. Refluxing Mn(NO₃)₂/bpy/phthalic acid reaction mixtures in CH₃CN leads to the isolation of 1, further concentration of the reaction solution in raising temperature results in 2. The Mn₁ and Mn₂ units in the inclusion compounds 1 and 2 are similar to other reported Mn₁ and Mn₂ analogs, respectively. The Jahn–Teller distortion was observed to give rise to the elongation along the O_terminal---Mn---O_carboxyl axes for all the four Mn(III) sites in 2, leading to unexpected longer Mn(III)---O_aqua than Mn(II)---O_aqua in 1. Extensive hydrogen bonding interactions among H₂O, NO₃ ⁻ and COOH were observed in the two inclusion compounds. Cyclic voltammetry of 2 in DMF displays two quasi-reversible redox couples at +0.10/+0.22 and −0.43/−0.36 V assigned to the Mn(III)Mn(IV)/2Mn(III) and 2Mn(III)/Mn(III)Mn(II), respectively. Variable temperature magnetic susceptibilities of 1 and 2 were measured. The data were fit to a model including axial zero-field splitting term and a good fit was found with D=1.77 cm⁻¹, g=1.98 and F=1.48×10⁻⁵ for 1. For 2, the least-squares fitting of the experimental data led to J=2.37 cm⁻¹, g=2.02 and D=0.75 cm⁻¹ with R=1.45×10⁻³.     

The respiratory chain of Azotobacter vinelandii II. The effect of cyanide on cytochrome d

1. Cyanide causes a slow disappearance of the oxidized band (648 nm) of cytochrome d in particles of Azotobacter vinelandii and inhibits the appearance of the reduced band (631 nm). No effect of cyanide is found on the reduced band of cytochrome d.

2. The kinetics of the disappearance of the 648-nm band of cytochrome d with excess cyanide deviates from first-order kinetics at lower temperatures (22 °C) indicating that at least two conformations of the enzyme are involved. At higher temperatures (32 °C) the observed kinetics of the cyanide reaction are first order with a k_on = 0.7 M⁻¹·s⁻¹ and with an estimated k_off of approximately 5·10⁻⁵ s⁻¹.

3. The value of the k_off (7·10⁻⁴−14·10⁻⁴ s⁻¹ at 32 °C) determined from the rate of reduction of cyanocytochrome d by Na₂S₂O₄ or NADH is one order of magnitude larger than the k_off value found when the enzyme is in its oxidized state.

4. No effect of cyanide is found on the spectrum of cytochrome a₁.     

The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution. Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO)5 anion

The complex [Et₄N][W(CO)₅OMe] (1) has been prepared from the reaction of the photochemically generated W(CO)₅THF adduct and [Et₄N][OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO)₄OMe]₂²⁻. The resulting THF insoluble salt [Et₄N]₂[W(CO)₄OMe]₂ (2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently react with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et₄N]₃[W₂(CO)₆(OMe)₃] (3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et₄N]₄[W(CO)₃OMe]₄ (4) which has been structurally characterized as a cubane-like arrangement with triply bridging μ³-methoxide groups and W(CO)₃ units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et₄N]₃[W₂(CO)₆(OCH₂CH₂OH)₃] (5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2₁/n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Å, β = 92.22(3)°, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Å, Z = 8, R = 8.13%. Crystal data for 5: space group P2₁2₁2₁, a = 11.43(2), b = 12.91(1), c = 29.85(6) Å, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et₄N][W(CO)₅OR] (R = C₆H₅ and 3,5-F₂C₆H₃) were measured to be 2.15 × 10⁻² and 1.31 × 10⁻³ s⁻¹, respectively, in THF solution at 5°C. Hence, the value of the rate constant of 2.15 × 10⁻² s⁻¹ establishes a lower limit for the first-order rate constant for CO loss in the W(CO)₅OMe⁻ anion, since the methoxide ligand is a better π-donating group than phenoxide.     

Reduction of ferricytochrome c by hydrogen atoms: Evidence for intramolecular transfer of reducing equivalent

Direct evidence obtained by means of the technique of pulse radiolysis-kinetic spectrometry, with measurements in the time range 10⁻⁶ to 1 s, is presented that, consequent upon reaction of a single H-atom with a single molecule of ferricytochrome c, a reducing equivalent is transmitted via the protein structure to the ferriheme moiety. Such transmission accounts for at least 70% of the total reduction of the ferri to the ferro state of cytochrome c. The remainder of the total reduction takes place without stages resolvable on the time scale of these experiments. Reduction brought about by H atoms appears to follow a different course than reduction by hydrated electrons. In the latter case, intramolecular transmission of reducing equivalents could not be demonstrated (Lichtin, N. N., Shafferman, A. and Stein, G. (1973) Biochim. Biophys. Acta 314, 117–135).

Not every H-atom reacts with ferricytochrome c at a site which results in conversion of the Fe(III) state to the Fe(II) state. Approximately half of reacting H-atoms do not produce reduction.

The following second order rate constants have been determined in solutions of low ionic strength at 20±2 °C: k[H+ferricytochrome c] = (1.0±0.2) · 10¹⁰ M⁻¹ · s⁻¹ at pH 3.0 and 6.7; k[H+ferrocytochrome c] = (1.3±0.2) · 10¹⁰ M⁻¹ · s⁻¹ at pH 3.0; k[e⁻_aq + ferrocytochrome c] = (1.9±0.4) · 10¹⁰ M⁻¹ · s⁻¹ at pH 6.7.     

Glutathione-proline activation of feeding behavior in the zoanthid Palythoa psammophilia Walsh & Bowers

Palythoa psammophilia Walsh & Bowers has a well coordinated, stereotyped feeding response, the culminating step of which is ingestion; this may be elicited by the synergistic effect of the tripeptide glutathione and the -imino acid, proline. Either activator acting separately causes responses only at high concentrations (above 10⁻⁵ M for glutathione; above 10⁻⁴ M for proline) in a reduced number of animals and at a low rate (5.00 ± 1.73 min in 5 × 10⁻³ M solutions of glutathione; 11.10±3.74 min in 5 × 10⁻³ M solutions of proline). Highest percentages of response were obtained in combinations where glutathione was at a concentration of 5 × 10⁻³ M and proline at 5 × 10⁻⁴ M or in combinations of glutathione at concentrations 5 × 10⁻⁶ M and proline at 5 × 10⁻⁵ M. The speed of ingestion is considerably enhanced when these activators are combined (1.17±1.18 min).     

Production d'NH4 par la crevette Crangon crangon L. dans deux écosystémes côtiers. approche expérimentale et étude de l'influence du sédiment sur le taux d'excrétion

Estimation of the ammonia production of the shrimp C. crangon in two littoral ecosystems (oligotrophic sand and eutrophic mud) was determined in winter and summer conditions from laboratory observations in experimental microcosms. The ammonia excretion rate of C. crangon was not influenced by either the sediment type or the ammonia concentration of the overlying water; on the other hand, the mean excretion rate and the response to initial handling stress increased markedly as shrimp were deprived of soft substratum.

The daily ammonia production of C. crangon was 16 μmol NH₃ · g ⁻¹ wet wt · day ⁻¹ in winter and 40 μmol in summer. A gross production of 12 μmol NH₃ · m⁻² · day ⁻¹ and 300–700 μmol μ m⁻² · day⁻¹, respectively, could be expected in the two ecosystems studied. This would account for 5% (winter) and 2–4% (summer) of the total NH⁺₄ flux at the sediment-water interface. The contribution of the excretion of all macrofauna to the NH⁺₄ flux from the sediment is discussed.     

Characterization of muscarinic acetylcholine receptors on the rat pancreatic gastrin-producing cell line B6 RIN

The mechanisms of cholinergic stimulation of gastrin cells were studied in the rat pancreatic cell line B6 RIN. Carbachol induced an increase in intracellular Ca²⁺ and stimulated gastrin release in a dose-dependent manner over the range 10⁻⁵-10⁻³ M. These effects were completely abolished by atropine, suggesting the implication of muscarinic cholinergic receptors. The binding properties of these receptors were investigated. [N-Methyl-³H]scopolamine ([³h]nms) binding on cell homogenates was time-dependent, saturable and consistent with a single high-affinity binding class (K_d = 39.5 pM, and B_max = 7.9 fmol/mg DNA). Carbachol competitively inhibited [³H]NMS binding. The potency of inhibition of [³H]NMS binding by subtype selective antagonists was hexahydrodifenidol> pirenzepine> AF-DX 116. These results suggest the M₃, muscarinic receptors may be involved in the carbachol-induced gastrin release from B6 RIN cells.     

Model reactions of a carbonylation catalyst: phosphite induced migratory CO insertion in [MeIr(CO)2I3]

Carbonylation of the anionic iridium(III) methyl complex, [MeIr(CO)₂I₃]⁻ (1) is an important step in the new iridium-based process for acetic acid manufacture. A model study of the migratory insertion reactions of 1 with P-donor ligands is reported. Complex 1 reacts with phosphites to give neutral acetyl complexes, [Ir(COMe)(CO)I₂L₂] (L = P(OPh)₃ (2), P(OMe)₃ (3)). Complex 2 has been isolated and fully characterised from the reaction of Ph₄As[MeIr(CO)₂I₃] with AgBF₄ and P(OPh)₃; comparison of spectroscopic properties suggests an analogous formulation for 3. IR and ³¹P NMR spectroscopy indicate initial formation of unstable isomers of 2 which isomerise to the thermodynamic product with trans phosphite ligands. Kinetic measurements for the reactions of 1 with phosphites in CH₂Cl₂ show first order dependence on [1], only when the reactions are carried out in the presence of excess iodide. The rates exhibit a saturation dependence on [L] and are inhibited by iodide. The reactions are accelerated by addition of alcohols (e.g. 18× enhancement for L = P (OMe)₃ in 1:3 MeOH-CH₂Cl₂). A reaction mechanism is proposed which involves substitution of an iodide ligand by phosphite, prior to migratory CO insertion. The observed rate constants fit well to a rate law derived from this mechanism. Analysis of the kinetic data shows that k₁, the rate constant for iodide dissociation, is independent of L, but is increased by a factor of 18 on adding 25% MeOH to CH₂Cl₂. Activation parameters for the k₁ step are ΔH^≠ = 71 (±3) kJ mol⁻, ΔS^≠ = −81 (±9) J mol⁻¹ K⁻¹ in CH₂Cl₂ and ΔH^≠ = 60(±4) kJ mol⁻¹, ΔS^≠ = −93(± 12) J mol⁻¹ K⁻¹ in 1:3 MeOH-CH₂Cl₂. Solvent assistance of the iodide dissociation step gives the observed rate enhancement in protic solvents. The mechanism is similar to that proposed for the carbonylation of 1.