Effect of oxygen and hypergravitation on alveolar surfactant

The effect of prolonged exposure (up to 66 hours) to pure oxygen breathing and to short (5-minute) oxygen breathing combined with acceleration (+5Gz) on the surface tension and surface potential of the alveolar washout of the albino rat lungs was determined. Both experimental conditions produced atelectasis and a decrease of the surfactant surface activity. Possible mechanisms of shifts of the surfactant activity under hyperoxia only, and hyperoxia with accelerations are discussed.     

Noninvasive Prenatal Testing Using Next Generation Sequencing: Pilot Experience of the D.O. Ott Research Institute of Obstetrics,Gynecology and Reproductology

Russian Journal of Genetics - In recent years, noninvasive prenatal testing (NIPT) for fetal chromosomal abnormalities has come into wide use. NIPT allows detection of fetal chromosomal...     

Excitation dynamics in strongly bounded associates of B800–850 and B800–830 complexes from photosynthetic purple bacterium Thiorhodospira sibirica

Strongly bounded associates of B800–850 (LH2) and B800–830 (LH3) complexes from photosynthetic purple bacterium Thiorhodospira sibirica were investigated. It was shown that associates contain 8–10 complexes (LH2:LH3 ≈ 1:1). Absorption spectra of the monomer LH2 and the monomer LH3 complexes were calculated. Excitation of B800 absorption band of associates results in: (i) intracomplex excitation energy transfer from B800 to B830 or B850 with time constant of about 500 fs; (ii) intercomplex excitation energy transfer from B820 band of LH3 complex to B850 band of LH2 complex with time constant of about 2.5 ps; (iii) excitation deactivation in B850 band of LH2 complex with time constant of about 800 ps. Signal polarization at long-wavelength side of associates absorption spectrum near 900 nm was negative (?0.1). The interaction of LH3 and LH2 complexes in associates is, to some extent, analogous to the interaction of LH2 and LH1 complexes in chromatophores. Time constant of excitation energy transfer between LH3 and LH2 complexes in associates may be regarded as a minimal time constant for energy transfer between the peripheral and core antenna complexes.     

Composition and catalase-like activity of Mn(II)-bicarbonate complexes

The composition and catalase-like activity of Mn2+ complexes with bicarbonate were investigated with voltammetry and kinetic methods (by the rate of O2 production from H2O2). Three linear sections were revealed on the dependence of the reduction potential of Mn2+ on logarithm of bicarbonate concentration (logC(NaHCO3)) having slopes equal to 0 mV/logC(NaHCO3), -14 mV/logC(NaHCO3), and -59 mV/logC(NaHCO3), corresponding to Mn2+ aqua complex (Mn2+(aq)) and to Mn2+-bicarbonate complexes of the composition [Mn2+(HCO3(-))]+ (at concentration of HCO3(-) 10-100 mM) and [Mn2+(HCO3(-))2]0 (at concentration of HCO3(-) 100-600 mM). Comparison of HCO3(-) concentration needed for the catalase-like activity of Mn2+ with the electrochemical data showed that only electroneutral complex Mn2+(HCO3(-))2 catalyzed decomposition of H2O2, whereas positively charged Mn2+(aq) complex and [Mn2+(HCO3(-))]+ were not active. The catalase-like activity of Mn2+ did not appear upon substitution of anions of carbonic acids (acetate and formate) for HCO3(-). The rate of O2 production in the system Mn2+-HCO3(-)-H2O2 (pH 7.4) is proportional to the second power of Mn2+ concentration and to the fourth power of HCO3(-) concentration that indicates simultaneous involvement of two Mn2+(HCO3(-))2 complexes in the reaction of H2O2 decomposition.     

Structural Model for Phenylalkylamine Binding to L-type Calcium Channels

Phenylalkylamines (PAAs), a major class of L-type calcium channel (LTCC) blockers, have two aromatic rings connected by a flexible chain with a nitrile substituent. Structural aspects of ligand-channel interactions remain unclear. We have built a KvAP-based model of LTCC and used Monte Carlo energy minimizations to dock devapamil, verapamil, gallopamil, and other PAAs. The PAA-LTCC models have the following common features: (i) the meta-methoxy group in ring A, which is proximal to the nitrile group, accepts an H-bond from a PAA-sensing Tyr_IIIS6; (ii) the meta-methoxy group in ring B accepts an H-bond from a PAA-sensing Tyr_IVS6; (iii) the ammonium group is stabilized at the focus of P-helices; and (iv) the nitrile group binds to a Ca²⁺ ion coordinated by the selectivity filter glutamates in repeats III and IV. The latter feature can explain Ca²⁺ potentiation of PAA action and the presence of an electronegative atom at a similar position of potent PAA analogs. Tyr substitution of a Thr in IIIS5 is known to enhance action of devapamil and verapamil. Our models predict that the para-methoxy group in ring A of devapamil and verapamil accepts an H-bond from this engineered Tyr. The model explains structure-activity relationships of PAAs, effects of LTCC mutations on PAA potency, data on PAA access to LTCC, and Ca²⁺ potentiation of PAA action. Common and class-specific aspects of action of PAAs, dihydropyridines, and benzothiazepines are discussed in view of the repeat interface concept.L-type calcium channels (LTCCs)² are targets for different drugs. Benzo(thi)azepines (BTZs), dihydropyridines (DHPs), and phenylalkylamines (PAAs) constitute the three major classes of the LTCC ligands (for reviews, see Refs. 1 and 2). All of these ligands bind to overlapping binding sites in the pore-forming domain of the α₁ subunit, but each class demonstrates unique characteristics of action. Depending on their chemical structure, DHPs act as agonists or antagonists (3). All known PAAs and BTZs are antagonists, but they have different access pathways to their binding sites: external for BTZs (4, 5) and predominantly internal for PAAs (6). Clinical use of verapamil in treatments of hypertension and arrhythmias (7) had stimulated intensive electrophysiological, mutational, and pharmacological studies involving PAAs.The pore-forming domain of LTCC includes the pore-lining inner helices S6, the outer helices S5, and the P-loops from all four repeats of the α₁ subunit. According to mutational analyses, the PAA-binding site is located in the interface between repeats III and IV. In particular, residues in transmembrane helices IIIS5, IIIS6, and IVS6 and P-loops of repeats III and IV contribute to binding of PAAs (8–14).Structure-activity relationships of PAAs were intensively studied (15–17). A common feature of potent PAAs is the presence of two methoxylated aromatic rings (named A and B). The rings are connected by a flexible alkylamine chain with a nitrile and an isopropyl group at the chiral tetrasubstituted carbon atom, which is proximal to ring A. Ring B is proximal to the amino group (see Fig. 1).Open in a separate windowFIGURE 1.Structural formulae of PAAs.Despite the fact that some specific contacts between functional groups of PAAs and PAA-sensing residues (residues that, when mutated, affect action of PAAs) have been proposed (10, 14), the flexibility of the ligands did not allow the characterization of the binding mode and the general pattern of ligand-channel interactions. In the absence of such knowledge, it is hardly possible to provide a molecular basis for structure-activity relationships. The problem is further complicated by the dependence of PAA action on the functional state of the channel, the ionic environment, the transmembrane voltage, and other factors. For example, it is generally believed that PAAs bind to the open/inactivated channels with higher affinities than to the closed state (for review, see Ref 1). However, the molecular basis for this state dependence is unclear.Lipkind and Fozzard (18) docked devapamil in a KcsA-based homology model of the L-type Ca²⁺ channel. They suggested an angular conformation of the drug, with ring B extended into the III/IV repeat interface and ring A in the central cavity. They also suggested that the protonated amino group of devapamil interacts directly with the selectivity filter glutamates. This model explains the effect of some mutations, particularly those in the P-loops and IVS6. However, other important aspects of PAA action such as the role of the nitrile group, the Ca²⁺ potentiation effect, and the effects of mutations in IIIS6 and IIIS5 remain unexplained.The gap between the amount of experimental data on PAA action and the level of understanding of the atomic level mechanisms necessitates further studies. In the absence of x-ray structures of Ca²⁺ channels, molecular modeling is the only available approach to address the structural aspects of PAA-LTCC interactions. Recently, we proposed molecular models for the action of other classes of L-type channel ligands. In the BTZ-LTCC models (19), the main body of the ligands binds in the repeat interface, whereas the amino group protrudes into the inner pore, where it is stabilized by nucleophilic C-terminal ends of the pore helices. In the DHP-LTCC models (20), the ligands also bind in the interface between repeats III and IV, whereas the moieties that differ between agonist and antagonists extend to the pore. Both models suggest direct interactions between the ligands and a Ca²⁺ ion bound to the selectivity filter glutamates in repeats III and IV.In this work, we elaborate molecular models for PAA·LTCC complexes that agree with a large body of experimental data. We further discuss common and different aspects of action of different ligands on LTCC and propose that certain aspects of the ligand action may be relevant to other P-loop channels.