Effects of prostaglandin E1 on contractility and Ca release in rabbit aortic smooth muscle

Concentrations of prostaglandin E₁ (PGE₁; 10⁻⁷ M) that do not elicit tension responses in aortic strips potentiate contractions induced by submaximal concentrations (10⁻⁸ − 10⁻⁷ M) of norepinephrine (NE) or angiotensin III (Ang III) but not those of high K⁺ depolarization or maximal NE or Ang III concentrations. Higher concentrations of PGE₁ (10⁻⁶ M and above) initiate contractions which are additive with submaximal responses to NE and Ang III but not to K⁺. These same concentrations of PGE₁ also decrease ⁴⁵Ca retention at high affinity La⁺⁺⁺-resistant sites in a manner similar to but not additive with NE and Ang III. Uptake of ⁴⁵Ca at low affinity La⁺⁺⁺-resistant sites (which is increased by high K⁺-depolarization) is not altered by 10⁻⁶ M PGE₁. The effects of PGE₁ are not altered by decreased extracellular Ca⁺⁺ (0.1 mM), decreased temperature, phentolamine or meclofenamate. Thus, PGE₁ does not appear to increase uptake of extracellular Ca⁺⁺ in this smooth muscle tissue. Instead, PGE₁ increases mobilization of Ca⁺⁺ from the same high affinity La⁺⁺⁺-resistant sites affected by Ang III and NE and, in this manner, may increase responses to these two stimulatory agents.     

Binding of Cu (II), Tb (III) and Fe (III) to chicken ovotransferrin

The kinetics of binding of Cu (II), Tb (III) and Fe(III) to ovotransferrin have been investigated using the stopped-flow technique. Rate constants for the second-order reaction, k ₊, were determined by monitoring the absorbance change upon formation of the metal-transferrin complex in time range of milliseconds to seconds. The N and C sites appeared to bind a particular metal ion with the same rate; thus, average formation rate constants k ₊ (average) were 2.4 × 10⁴ M^–1 s^–1 and 8.3 × 10⁴ M^–1 S ^–1 for Cu (II) and Tb (III) respectively. Site preference (N site for Cu (II) and C site for Tb (III)) is then mainly due to the difference in dissociation rate constant for the metals. Fe (III) binding from Fe-nitrilotriacetate complex to apo-ovotransferrin was found to be more rapid, giving an average formation rate constant k ₊ (average) of 5 × 10⁵ M^–1 s^–1, which was followed by a slow increase in absorbance at 465 nm. This slow process has an apparent rate constant in the range 3 s^–1 to 0.5 s^–1, depending upon the degree of Fe (III) saturation. The variation in the rate of the second phase is thought to reflect the difference in the rate of a conformational change for monoferric and diferric ovotransferrins. Monoferric ovotransferrin changes its conformation more rapidly (3.4s^–1) than diferric ovotransferrin (0.52 s^–1). A further absorbance decrease was observed over a period of several minutes; this could be assigned to release of NTA from the complex, as suggested by Honda et al. (1980).Abbreviations Tf ovotransferrin - NTA nitrilotriacetate Jichi Medical School, School of Nursing, Yakushiji 3311-159, Minamikawachi, Tochigi, 329-04 Japan     

Reaction of trans-dichlorobis(ethylenediamine)nickel(III) in aqueous hydrochloric acid

Both EPR and electronic absorbance spectroscopy have been used to follow the disappearance of [Ni^III(en)₂Cl₂]⁺ in aqueous HCI solutions. The rate of Ni(III) reduction is influenced by both the H⁺ and Cl^? concentrations, although the rate is not linear with respect to the concentration of either species. A mechanism is proposed in which the first step in the reaction is the proton-induced chelate ring opening which is followed by the reduction of Ni(III) by chloride ions. In the presence of H₂SO₄ the coordinated Cl^? ions are rapidly replaced by HSO_4^? ions and the resulting complex is much more stable, even in a 6 N acid solution.     

Dual effect of adrenalin on sugar transport in rat diaphragm muscle

The effect of adrenalin on the membrane transport of the non-metabolized sugar, 3-methylglucose, was studied in isolated “intact” rat hemidiaphragms and related to simultaneously occurring changes in the internal levels of Na⁺, ATP, glucose-6-P, glycerol formation and ⁴⁵Ca uptake and loss. Basal sugar transport was inhibited by low (10⁻⁸−10⁻⁵ M) concentrations of adrenalin; this was antagonized by propranolol and practolol. High concentrations (10⁻⁴−10⁻³ M) stimulated sugar transport, and this was blocked by propranolol and butoxamine and was dependent on external Ca²⁺. These results suggest interaction with two different classes of adrenergic receptors, possibly of β₁ and β₂ types. Both low and high concentrations increased Na⁺ and K⁺ gradients by a practolol-sensitive effect. Isoproterenol behaved identically but phenylephrine had only the two practolol-sensitive effects on sugar and ion transport. Insulin did not interfere with inhibition of sugar transport and decrease in internal Na⁺ but prevented stimulation of sugar transport. Under anoxia adrenalin had no effect on sugar transport but led to greater Na⁺ gain by tissue. Addition of 3.0 mM palmitate decreased inhibition of sugar transport without changing receptor specificity. ATP was decreased and lipolysis enchanged by high adrenalin but glucose-6-P was increased by the low concentration as well. Influx of ⁴⁵Ca was decreased by low and increased by high adrenalin; ⁴⁵Ca efflux was also differentially affected. The results indicate that inhibition and stimulation of sugar transport depend on different receptors and that the latter response may override the former. The data are consistent with the earlier postulated regulatory role of sarcoplasmic Ca²⁺ on sugar transport in muscle, with adrenalin affecting Ca²⁺ fluxes and distribution both directly and indirectly.     

Gill (Na+,K+)-ATPase from the blue crab Callinectes danae: modulation of K+-phosphatase activity by potassium and ammonium ions

The kinetic properties of a microsomal gill (Na⁺,K⁺)-ATPase from the blue crab Callinectes danae were analyzed using the substrate p-nitrophenylphosphate. The (Na⁺,K⁺)-ATPase hydrolyzed PNPP obeying cooperative kinetics (n=1.5) at a rate of V=125.4±7.5 U mg⁻¹ with K_0.5=1.2±0.1 mmol l⁻¹; stimulation by potassium (V=121.0±6.1 U mg⁻¹; K_0.5=2.1±0.1 mmol l⁻¹) and magnesium ions (V=125.3±6.3 U mg⁻¹; K_0.5=1.0±0.1 mmol l⁻¹) was cooperative. Ammonium ions also stimulated the enzyme through site–site interactions (n_H=2.7) to a rate of V=126.1±4.8 U mg⁻¹ with K_0.5=13.7±0.5 mmol l⁻¹. However, K⁺-phosphatase activity was not stimulated further by K⁺ plus NH₄⁺ ions. Sodium ions (K_I=36.7±1.7 mmol l⁻¹), ouabain (K_I=830.3±42.5 μmol l⁻¹) and orthovanadate (K_I=34.0±1.4 nmol l⁻¹) completely inhibited K⁺-phosphatase activity. The competitive inhibition by ATP (K_I=57.2±2.6 μmol l⁻¹) of PNPPase activity suggests that both substrates are hydrolyzed at the same site on the enzyme. These data reveal that the K⁺-phosphatase activity corresponds strictly to a (Na⁺,K⁺)-ATPase in C. danae gill tissue. This is the first known kinetic characterization of K⁺-phosphatase activity in the portunid crab C. danae and should provide a useful tool for comparative studies.     

Decarboxylation kinetics for the carbonatotris(pyridine)cobalt(III) ion in perchloric acid solutions

The kinetics of the decomposition reactions of the CO(py)₃(CO₃)(H₂O)⁺ ion have been investigated in aqueous perchloric acid solutions over a range of hydrogen ion concentrations (0.10 to 5.0 M) and at two ionic strengths (I = 1.0 and 5.0 M). At the lower ionic strength, plots of ln (A_t–A_∞ versus time show a nonlinearity that is consistent with that expected for consecutive first-order reactions. The rates of the faster reaction are similar to those reported for the spontaneous reduction of aquopyridine-cobalt(III) cations. At the higher ionic strength, the above noted curvature is not apparent and the decarboxylation kinetics of the title complex may be described by a pseudo-first-order rate constant: k_obs = k[H₃O⁺]. At 20°C, k = (1.75−+0.09) s⁻¹ M⁻¹ with activation parameters ofΔH^‡ = (97 −+ 4) kJ mol⁻¹ and ΔS^‡ = −(54 −+ 32) J deg⁻¹ mol⁻¹. These kinetic parameters are compared with those previously reported for the similar complexes, Co(py)₄CO₃⁺ and Co(py)₂(CO₃)(H₂O)₂⁺.     

The hemoglobin of the crossopterygian fish, Latimeria chalumnae (Smith). Subunit structure and oxygen equilibria

There are five oxidation-reduction states of horseradish peroxidase which are interconvertible. These states are ferrous, ferric, Compound II (ferryl), Compound I (primary compound of peroxidase and H₂O₂), and Compound III (oxy-ferrous). The presence of heme-linked ionization groups was confirmed in the ferrous enzyme by spectrophotometric and pH stat titration experiments. The values of pK were 5.87 for isoenzyme A and 7.17 for isoenzymes (B + C). The proton was released when the ferrous enzyme was oxidized to the ferric enzyme while the uptake of the proton occurred when the ferrous enzyme reacted with oxygen to form Compound III. The results could be explained by assuming that the heme-linked ionization group is in the vicinity of the sixth ligand and forms a stable hydrogen bond with the ligand.The measurements of uptake and release of protons in various reactions also yielded the following stoichiometries: Ferric peroxidase + H₂O₂ → Compound I, Compound I + e^? + H⁺ → Compound II, Compound II + e^? + H⁺ → ferric peroxidase, Compound II + H₂O₂ → Compound III, Compound III + 3e^? + 3H⁺ → ferric peroxidase.Based on the above stoichiometries and assuming the interaction between the sixth ligand and heme-linked ionization group of the protein, it was possible to picture simple models showing structural relations between five oxidation-reduction states of peroxidase. Tentative formulae are as follows: [Pr·Po·Fe-(II) $\text{\$}\text{?}$PrH⁺·Po·Fe(II)] is for the ferrous enzyme, Pr·Po·Fe(III)OH₂ for the ferric one, Pr·Po·Fe(IV)OH^? for Compound II, Pr(OH^?)·Po⁺·Fe(IV)OH^? for Compound I, and PrH⁺·Po·Fe(III)O₂^? for Compound III, in which Pr stands for protein and Po for porphyrin. And by Fe(IV)OH^?, for instance, is meant that OH^? is coordinated at the sixth position of the heme iron and the formal oxidation state of the iron is four.     

Low prostaglandin concentrations cause cardiac rhythm disturbances. Effect reversed by low levels of copper or chloroquine

IN perfused male rat hearts concentrations of prostaglandins (PGs) E2 and F2α in the range 1 pg/ml to 10 ng/ml (2.8 × 10⁻¹² to 2.8 × 10⁻⁸M) consistently caused rhythm irregularities. Higher concentrations had no effect themselves and stabilized rhythm in hearts made unstable by lower concentrations. Copper ions (as the sulphate) at 2 × 10⁻⁶M stabilized hearts made unstable by PGs and when present prior to the PGs prevented PG induced disturbances. Chloroquine also reversed PG-induced rhythm changes.     

The structures of bis(1H,5H-S-methylisothiocarbonohydrazidium) di-μ-chloro-octachlorodibismuthate(III) tetrahydrate and tris(1H-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III)

The structures of bis(1H⁺,5H⁺-S-methylisothiocarbonohydrazidium) di-μ-chlorooctachlorodibismuthate(III) tetrahydrate: (C₂H₁₀N₄S)₂(Bi₂Cl₁₀)· 4H₂O (compound [I]) and of tris(1H⁺-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III): (C₂H₉N₄S)₃(BiCl_5.67I_0.33) (compound [II]) were determined from single crystal X-ray diffractometer data. Both compounds crystallize as triclinic (P ); crystals [I] with Z = 1 formula unit in a cell of constants: A = 10.621(3), B = 9.989(5), C = 7.439(3) Å, α = 88.31(2), β = 84.51(2), γ = 68.88(2)°, final R = 0.0427 for 2229 unique reflections with I 2σ(I); crystals [II] with Z = 2 and cell dimensions: A = 14.109(4), B = 12.209(9), C = 8.206(7) Å, α = 103.54(3), β = 104.95(2), γ = 81.96(2)°, final R = 0.0411 for 3637 unique reflections (1 2σ(I)). The structure of [I] is built up of diprotonated organic cations, water molecules and dinuclear centrosymmetric [Bi₂Cl₁₀]⁴⁻ anions held together by N-HCl, N-HO, O-HCl hydrogen bonds and Van der Waals interactions. The [Bi₂Cl₁₀]⁴⁻ complex consists of two edge-sharing octahedra in which three pairs of bonds of similar length are observed (Bi-Cl_av = 2.602(5), 2.712(4), 2.855(5) Å). The structure of [II] consists of monoprotonated cations and [BiCl_5.67I_0.33]³⁻ anions held together by a tridimensional network of hydrogen bonds. Each bismuth atom is octahedrally surrounded by six chlorine atoms, one of which is statistically substituted by a iodine atom.     

Growth responses of the perennial legume Sesbania sesban to NH4 and NO3 nutrition and effects on root nodulation

Preference for NH₄⁺ or NO₃⁻ nutrition by the perennial legume Sesbania sesban (L.) Merr. was assessed by supplying plants with NH₄⁺ and NO₃⁻ alone or mixed at equal concentrations (0.5 mM) in hydroponic culture. In addition, growth responses of S. sesban to NH₄⁺ and NO₃⁻ nutrition and the effects on root nodulation and nutrient and mineral composition of the plant tissues were evaluated in a hydroponic setup at a range of external concentration of NH₄⁺ and NO₃⁻ (0, 0.1, 0.2, 0.5, 2 and 5 mM). Seedlings of S. sesban grew equally well when supplied with either NH₄⁺ or NO₃⁻ alone or mixed and had high relative growth rates (RGRs) ranging between 0.19 and 0.21 d⁻¹. When larger plants of S. sesban were supplied with NH₄⁺ or NO₃⁻ alone, the RGRs and shoot elongation rates were not affected by the external concentration of inorganic N. At external N concentrations up to 0.5 mM nodulation occurred and contributed to the N nutrition through fixation of gaseous N₂ from the atmosphere. For both NH₄⁺ and NO₃⁻-fed plants the N concentration in the plant tissues, particularly water-extractable NO₃⁻, increased at high supply concentrations, and concentrations of mineral cations generally decreased. It is concluded that S. sesban can grow without an external inorganic N supply by fixing atmospheric N₂ gas via root nodules. Also, S. sesban grows well on both NH₄⁺ and NO₃⁻ as the external N source and the plant can tolerate relatively high concentrations of NH₄⁺. This wide ecological amplitude concerning N nutrition makes S. sesban very useful as a N₂-fixing fallow crop in N deficient areas and also a candidate species for use in constructed wetland systems for the treatment of NH₄⁺ rich waters.     

Cl−HCO3 exchange in rat renal basolateral membrane vesicles

Pathways for HCO₃⁻ transport across the basolateral membrane were investigated using membrane vesicles isolated from rat renal cortex. The presence of Cl⁻---HCO₃⁻ exchange was assessed directly by ³⁶Cl⁻ tracer flux measurements and indirectly by determinants of acridine orange absorbance changes. Under 10% CO₂/90% N₂ the imposition of an outwardly directed HCO₃⁻ concentration gradient (pH_o 6/pH_i 7.5) stimulated Cl⁻ uptake compared to Cl⁻ uptake under 100% N₂ in the presence of a pH gradient alone. Mediated exchange of Cl⁻ for HCO₃ was suggested by the HCO₃⁻ gradient-induced concentrative accumulation of intravesicular Cl⁻. Maneuvers designed to offset the development of ion-gradient-induced diffusion potentials had no significant effect on the magnitude of HCO₃⁻ gradient-driven Cl⁻ uptake further suggesting chemical as opposed to electrical Cl−HCO₃⁻ exchange coupling. Although basolateral membrane vesicle Cl⁻ uptake was observed to be voltage sensitive, the DIDS insensitivity of the Cl conductive pathway served to distinguish this mode of Cl⁻ translocation from HCO₃ gradient-driven Cl⁻ uptake. No evidence for cotransport was obtained. As determined by acridine orange absorbance measurements in the presence of an imposed pH gradient (pH_o 7.5/pH_i 6), a HCO₃⁻ dependent increase in the rate of intravesicular alkalinization was observed in response to an outwardly directed Cl⁻ concentration gradient. The basolateral membrane vesicle origin of the observed Cl⁻−HCO₃⁻ exchange activity was verified by experiments performed with purified brush-border membrane vesicles. In contrast to our previous observations of the effect of Cl⁻ on HCO₃⁻ gradient-driven Na⁺ uptake suggesting a basolateral membrane Na⁺−HCO₃⁻ for Cl⁻ exchange mechanism, no effect of Na⁺ on Cl−HCO₃⁻ exchange was observed in the present study.     

The role of chloride in O2 evolution by thylakoids from salt-tolerant higher plants

(1) Thylakoids isolated from leaves of two salt-tolerant higher plant species were found to require high (greater than 250 mM) concentrations of Cl⁻ for maximal rates of photosynthetic O₂ evolution and maximum variable chlorophyll a fluorescence yield. These activities were also tolerant to extremely high (2–3 M) salt concentrations. Their pH dependence was markedly different in the absence and presence of sufficient salt levels. (2) When Cl⁻ was provided as CaCl₂, as opposed to MgCl₂, KCl or NaCl, higher rates of O₂ evolution were obtained, suggesting that Ca²⁺ has an important role in Photosystem II reactions. (3) The site of Cl⁻ action was located on the electron donor side of Photosystem II. (4) O₂ evolution in the presence of optimal Cl⁻ concentrations showed a pH dependence closely matched by that of ³⁵Cl-NMR line broadening, which is indicative of Cl⁻ binding. This pH-dependent ³⁵Cl-NMR line-width broadening was not altered significantly by treatment of the thylakoids with EDTA; it was, however, abolished by heat treatment. (5) Only anions with similar ionic radii (Br⁻, NO⁻₃) were effective in replacing Cl⁻. Small anions such as F⁻ and OH⁻ were inhibitory; larger ions had no effect. The inhibition by F⁻ is due, at least in part, to displacement of Cl⁻. The selectivity is attributed to a combination of steric and ionic field effects. (6) It is proposed that Cl⁻ facilitates Photosystem II electron transport by reversible ionic binding to the O₂-evolving complex itself or to the thylakoid membrane in close proximity to it.     

Laser raman studies of molecular interactions with phosphatidylcholine multilayers. II. Effects of mono- and divalent ions on bilayer structure

Laser Raman spectroscopy was applied to characterize structural behavior of dipalmitoyl phosphatidylcholine multibilayer systems in the presence of several cations (K⁺, Na⁺, Cs⁺, Rb⁺, Ca²⁺, Mg²⁺, Cd²⁺, Ba²⁺) and anions (Cl⁻, Br⁻, I⁻, NO₃⁻, SO₃²⁻, SO₄²⁻, S₂O₃²⁻, S₂O₈²⁻). To evaluate the Raman-spectroscopical data quantitatively, characteristic intensity ratios, lateral and trans order parameters were used and compared. It was shown that the different trans order parameters are rather sensitive to ion-polar head group interactions and thus, they cannot give unequivocal information on the trans-gauche isomerization of hydrocarbon chains of phospholipids. The observed effects of ions on Raman spectra of phospholipid multilayers could not be explained simply on the basis of electrostatic interactions. The possible involvement of other factors (changes in polarizability, hydrogen bonds, etc.) is also discussed. It was demonstrated that the order parameters defined in different ways may result in different effectiveness sequences of ions. Of monopositive ions Na⁺ was found to be the most effective to influence the bilayer structure. For dipositive ions, of which Ca²⁺ proved to be the most effective, concentration-dependent effectiveness sequences were obtained. A plausible interpretation and some consequences of the concentration-dependent two-step binding of divalent cations were also outlined. Bilayered phospholipid structures turned out to be more responsive to anions than to most cations investigated. Interdependent actions of cations and anions, as well as the possible relevance of the charge distribution on anions are postulated.     

Dinuclear complexes of transition metals containing carbonate ligands. VIII. Kinetics and mechanism of carbon dioxide uptake by the tri-μ-hydroxo-bis (1,5-diamino-3-aza-pentane)cobalt(III) ion in weakly basic aqueous carbonate solution

The kinetics of formation of the complex ion, μ-carbonato-di-μ-hydroxo-bis((1,5-diamino-3-aza-pentane) cobalt(III), from the tri-μ-hydroxo-bis((1,5-diamino-3-aza-pentane(III)cobalt(III)) ion in aqueous buffered carbonate solution have been studied spectrophotometrically at 295 nm over the ranges 20.0θ°C34.8, 8.03pH9.44, 5 mM [CO₃²⁻35 mM and at an ionic strength of 0.1 M (LiClO₄). On the basis of the kinetic results a mechanism, involving rapid cleavage of an hydroxo bridge followed by carbon dioxide uptake with subsequent bridge formation, has been proposed. At 25 °C, the rate of the carbon dioxide uptake is 0.58 M⁻¹ s⁻¹ with ΔH≠ = (13.2±0.7) kcal mol⁻¹ and ΔS≠ = (−15.1 ± 0.7) cal deg⁻¹ mol⁻¹. The results are composed with those obtained for several mononuclear cobalt(III) and one dinuclear cobalt(III) complexes.     

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO₃⁻-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO₃⁻-N treatments for 20 days. The contents of Na⁺ and Cl⁻ were higher, but NO₃⁻ was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na⁺ to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl⁻ was lower, but NO₃⁻ concentration and the estimated contribution of NO₃⁻ to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl⁻ to a lower level, and accumulate NO₃⁻ even with low soil NO₃⁻ concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.     

Vanadate inhibition of the Ca-ATPase from human red cell membranes

1. (1) VO₃⁻ combines with high affinity to the Ca²⁺-ATPase and fully inhibits Ca²⁺-ATPase and Ca²⁺-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state level of the Ca²⁺-dependent phosphoenzyme.

2. (2) VO₃⁻ blocks hydrolysis of ATP at the catalytic site. The sites for VO₃⁻ also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca²⁺-ATPase.

3. (3) The sites for VO₃⁻ show positive interactions in affinity with sites for Mg²⁺ and K⁺. This accounts for the dependence on Mg²⁺ and K⁺ of the inhibition by VO₃⁻. Although, with less effectiveness, Na⁺ substitutes for K⁺ whereas Li⁺ does not. The apparent affinities for Mg²⁺ and K⁺ for inhibition by VO₃⁻ seem to be less than those for activation of the Ca²⁺-ATPase.

4. (4) Inhibition by VO₃⁻ is independent of Ca²⁺ at concentrations up to 50 μM. Higher concentrations of Ca²⁺ lead to a progressive release of the inhibitory effect of VO₃⁻.

Prostaglandin E2 and atriopeptin III oppose the contractile effect of angiotensin II in rat kidney mesangial cell cultures

Effects of vasoconstrictory and of dilatory hormones were studied on the contractile activity of cultured rat kidney mesangial cells. By phase contrast microscopy, a rapid contraction was seen of most cells treated with angiotensine II (10⁻⁶ − 10⁻¹⁰ mol/L), which was sometimes followed by autonomous relaxation after 10 to 20 min. Prostaglandin E₂ and antriopeptin III prevented the contractile effect of angiotensin II in a dose-dependent manner. Angiotensin II, but not atriopeptine III, stimulated prostaglandin E₂ synthesis in mesangial cell cultures.     

Effect of ions on phospholipid layer structure as indicated by Raman Spectroscopy

Various anions and cations are found to induce changes in the layered structure of phosphatidylcholine-water systems as indicated by Raman Spectroscopy. From the ratio of Raman intensities, , it is inferred that dispositive ions decrease the proportion of gauche character in the hydrocarbon chains, with the relative influence being: Ba²⁺ < Mg²⁺ < Ca²⁺ ≈ Cd²⁺. Unipositive ions (Li⁺, K⁺ and Na⁺) produce no observed changes in the Raman spectrum of the lecithin dispersion. The proportion of gauche character of the hydrocarbon chains is found to be nearly independent of the anion for: Br⁻, Cl⁻, acetate⁻, I⁻, ClO₄⁻, CNS⁻ and SO₄²⁻. Dispersions prepared with a solution of KI + I₂ produced Raman spectra in which the 1089 cm⁻¹ peak, which is characteristic of random lipid chains, was greatly intensified, presumably because of the presence of I₃⁻ which is known to penetrate the lipid lamellae. The observed trends are discussed.     

Kinetics of delayed chlorophyll a fluorescence registered in milliseconds time range

Delayed fluorescence dark decays in the time interval from 0.35 to 5.5ms are measured during dark to light adaptation in whole barley leaves and isolated thylakoid membranes, using a disc phosphoroscope. The changes in delayed fluorescence features are compared with variable chlorophyll fluorescence simultaneously registered with the same apparatus as well as in parallel by Handy PEA (Hansatech Instruments Ltd.), and absorbance changes at 820 nm. The registered delayed fluorescence signal is a sum of three components – submillisecond with lifetime of about 0.6 ms, millisecond decayed 2–4 ms and slow component with lifetime > >5.5 ms. The submillisecond delayed fluorescence component is proposed to be a result of radiative charge recombination in Photosystem II reaction centers in the state Z⁺PQ_A⁻Q_B⁻, and its lifetime is determined by the rate of electron transfer from Q_A⁻ to Q_B⁻. The millisecond delayed fluorescence component is associated with recombination in Z⁺PQ_A⁻Q_B⁼ centers with a lifetime determined by the sum of the rate constants of electron transfer from the oxygen-evolving complex to Z⁺ and of the exchange between the reduced and oxidized plastoquinone pool in the Q_B-site. On the basis of these assumptions and of the different share of the three components in the integral delayed fluorescence during induction, an attempt has been made to interpret the changes in the delayed fluorescence intensity during the transition of the photosynthetic apparatus from dark to light adapted state.     

Interactions of cardiac glycosides with cells and membranes Properties and structural aspects of two receptor sites for ouabain in erythrocytes

The existence of two types of binding sites for ouabain in human erythrocyte membranes is described. Receptor sites designated as ‘type I’, which may be identical to the K⁺-insensitive sites of intact cells, were detected at concentrations of ouabain as low as 10⁻⁷ M. The ‘type II’ receptor sites require the inclusion of Mg²⁺ + P_i to form complexes with ouabain; they may be identical to the K⁺-sensitive sites of intact cells. These sites were saturated at approx. 5 · 10⁻⁷ M ouabain but could not be detected at higher concentrations. The range of ouabain concentrations at which ‘type I’ receptors start to predominate (i.e. 5 · 10⁻⁸–5 · 10⁻⁷ M) was termed ‘critical digitalis concentrations’. The process of binding reached equilibrium within 1 and 4 h for ‘type I’ and ‘type II’ sites, respectively. The dissociation constant for ‘type II’ receptor-ouabain complexes was 7.6 · 10⁻⁹ M.Under similar experimental conditions, rat erythrocyte membranes exhibited only non-saturable sites.Alterations in the proportions of the two types of receptors were demonstrated by preincubation of the membranes, in the presence or absence of Mg²⁺ + P_i, prior to the addition of ouabain. In the first case, ‘type II receptor-ouabain’ complexes were stabilized at about 50% of the untreated membranes and ‘type I-ouabain’ complexes slowly approached equilibrium over a period of 24 h. In the latter instance, ‘type I’ receptors were not detected, and only ‘type II-ouabain’ complexes prevailed.