Responsiveness of cardiac Na+ channels to antiarrhythmic drugs: The role of inactivation

Summary Elementary Na⁺ currents were recorded at 9°C in inside-out patches from cultured neonatal rat heart myocytes. In characterizing the sensitivity of cooled, slowly inactivating cardiac Na⁺ channels to several antiarrhythmic drugs including propafenone, lidocaine and quinidine, the study aimed to define the role of Na⁺ inactivation for open channel blockade.In concentrations (1–10 mol/liter) effective to depressNP _o significantly, propafenone completely failed to influence the open state of slowly inactivating Na⁺ channels. With 1 mol/liter, _open changed insignificantly to 96±7% of the control. Even a small number of ultralong openings of 6 msec or longer exceeding _open of the whole ensemble several-fold and attaining _open (at –45 mV) in cooled, (-)-DPI-modified, noninactivating Na⁺ channels proved to be drug resistant and could not be flicker-blocked by 10 mol/liter propafenone. The same drug concentration induced in(-)-DPI-modified Na⁺ channels a discrete block with association and dissociation rate constants of 16.1 ± 5.3 × 10⁶ mol^–1 sec^–1 and 675 ± 25 sec^–1, respectively. Quinidine, known to have a considerable affinity for activated Na⁺ channels, in lower concentrations (5 mol/liter) left _open unchanged or reduced, in higher concentrations (10 mol/liter) _open only slightly to 81% of the predrug value whereasNP _o declined to 30%, but repetitive blocking events during the conducting state could never be observed. Basically the same drug resistance of the open state was seen in cardiac Na⁺ channels whose open-state kinetics had been modulated by the cytoplasmic presence of F^– ions. But in this case, propafenone reduced reopening and selectively abolished a long-lasting open state. This drug action is unlikely related to the inhibitory effect onNP _o since hyperpolarization and the accompanying block attenuation did not restore the channel kinetics. It is concluded that cardiac Na⁺ channels cannot be flicker-blocked by antiarrhythmic drugs unless Na⁺ inactivation is removed.     

The relation of proton motive force,adenylate energy charge and phosphorylation potential to the specific growth rate and efficiency of energy transduction inBacillus licheniformis under aerobic growth conditions

The magnitude of the proton motive force (p) and its constituents, the electrical () and chemical potential (-ZpH), were established for chemostat cultures of a protease-producing, relaxed (rel ^–) variant and a not protease-producing, stringent (rel ⁺) variant of an industrial strain ofBacillus licheniformis (respectively referred to as the A- and the B-type). For both types, an inverse relation of p with the specific growth rate was found. The calculated intracellular pH (pH_in) was not constant but inversely related to . This change in pH_in might be related to regulatory functions of metabolism but a regulatory role for pH_in itself could not be envisaged. Measurement of the adenylate energy charge (EC) showed a direct relation with for glucose-limited chemostat cultures; in nitrogen-limited chemostat cultures, the EC showed an approximately constant value at low and an increased value at higher . For both limitations, the ATP/ADP ratio was directly related to .The phosphorylation potential (G'p) was invariant with . From the values for G'p and p, a variable H⁺/ATP-stoichiometry was inferred: H⁺/ATP=1.83+0.52µ, so that at a given H⁺/O-ratio of four (4), the apparent P/O-ratio (inferred from regression analysis) showed a decline of 2.16 to 1.87 for =0 to _max (we discuss how more than half of this decline will be independent of any change in internal cell-volume). We propose that the constancy of G'p and the decrease in the efficiency of energy-conservation (P/O-value) with increasing are a way in which the cells try to cope with an apparent less than perfect coordination between anabolism and catabolism to keep up the highest possible with a minimum loss of growth-efficiency. Protease production in nitrogen-limited cultures as compared to glucose-limited cultures, and the difference between the A- and B-type, could not be explained by a different energy-status of the cells.Abbreviations CCCP carbonylcyanide-p-trichloromethoxyphenylhydrazone - DW dry weight of biomass - F Faraday's constant, 96.6 J/(mV × mol) - Fo chemostat outflow-rate (ml/h) - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone - G'p phosphorylation potential, the Gibbs energy change for ATP-synthesis from ADP and P_i - G'⁰p standard Gibbs energy change at specified conditions - H⁺/ATP number of protons translocated through - ATP synthase in synthesis of one ATP - H⁺/O protons translocated during transfer of 2 electrons from substrate to oxygen - specific growth rate (1/h) - _H+ transmembrane electrochemical proton potential, J/mol - M_b molar weight (147.6 g/mol) of bacteria with general cell formula C_6.0H_10.8O_3.0N_1.2 - pH_out,in extracellular, intracellular pH - P_i (intracellular) inorganic phosphate - p proton motive force, mV - pH transmembrane pH-difference - transmembrane electrical potential, mV - P/O number of ADP phosphorylated to ATP upon reduction of one O^2– to H₂O by two electrons transferred through the electron transfer chain - P/O (H⁺/O) × (H⁺/ATP)^–1 - P/O_F, P/O_N P/O with the two electrons donated by resp. (NADH + H⁺) and FADH - q specific rate of consumption or production (mol/g DW × h) - rel ⁺,rel ^– stringent, relaxed genotype - R universal gas constant, 8.36 J/(mol × degree) - T absolute temperature - TPMP⁺ triphenylmethylphosphonium ion - TPP⁺ tetraphenyl phosphonium ion - Y growth yield, g DW/mol - Z conversion constant=61.8 mV for 310 K (37 °C) - ZpH transmembrane proton potential or chemical potential, mV     

Control of basidiospore production by a nuclear gene in the fungus Coprinus congregatus

Summary The genetical control of basidiospore production by sporophores of the fungus Coprinus congregatus was studied. This species is characterized by a bipolar compatibility control, and homokaryons with complementary alleles A1 and A2 can be distinguished apart. We confirmed that the pale mushroom phenotype of the fungus is determined by a nuclear gene symbolized pal. This gene also controls a sporeless character and segregates independently of the mating-type locus. Dikaryons homoallelic for the pal ^– allele produce typical pale and sporeless sporophores, while heteroallelic (pal ⁺, pal ^–) and homoallelic (pal ⁺, pal ⁺) dikaryons produce normal or almost normal sporulating sporophores. In order to segregate homokaryons homoallelic for the pal gene (A1, pal ^–; A1, pal ⁺, A2, pal ^–; A2, pal ⁺), the following protocols were used: (a) the dikaryotization of stock homokaryons containing the pal ⁺ allele and of each mating type, A1 or A2, by dikaryotic mycelia homoallelic for the pal ^– allele; (b) the culturing of homokaryotic mycelia issuing from the germination of basidiospores from sporophores produced by dikaryotic mycelia heterokaryotic for the pal gene; (c) the culturing of mycelia grown from protoplasts obtained from dikaryons homoallelic for the pal ^– allele (D6 strain), and from homokaryons heteroallelic for the pal gene (H8), or homoallelic for pal ^#x002B;+ allele (H7). These techniques enabled us to segregate homokaryons of the four types defined above and were indispensable in the segregation of the pal ^– homoallelic homokaryons as no basidiospores were produced by typical pale mushrooms.     

Effects of the growth regulator 4PU-30 on growth,K+ content,and alkaloid production in tobacco callus cultures

Growth, K⁺ content, and alkaloid production were compared in nonorganogenetic callus cultures ofNicotiana tabacum cv. Burley 21 grown at 25°C in the dark on two different media: a basal medium with 1 M -naphthaleneacetic acid and 1 M kinetin, and one with 1 M -naphthaleneacetic acid and 1 M 4PU-30 (N-(2-chloro-4-pyridyl)-N-phenylurea). These callus tissues behaved differently not only in growth and K⁺ content but also in alkaloid production. In comparison to cultures grown with kinetin, those grown with 4PU-30 showed a significantly higher fresh weight and dry weight and K⁺ content during the growth period studied. The data clearly indicate a positive correlation between K⁺ uptake rate stimulated by 4PU-30 and cell enlargement rate. However, the alkaloid biosynthesis in the callus tissues was activated by the supply of kinetin and diminished by that of 4PU-30. It thus appears that cellular enlargement of meristematic tissue stimulated by 4PU-30 limited alkaloid production.     

Effect of Extracellular pH on Presteady-State and Steady-State Current Mediated bythe Na<Superscript>+</Superscript>/K<Superscript>+</Superscript> Pump

A ouabain sensitive inward current occurs in Xenopus oocytes in Na⁺ and K⁺ -free solutions. Several laboratories have investigated the properties of this current and suggested that acidic extracellular pH (pH_o) produces a conducting pathway through the Na⁺/K⁺ pump that is permeable to H⁺ and blocked by [Na⁺]_o. An alternative suggestion is that the current is mediated by an electrogenic H⁺-ATPase. Here we investigate the effect of pH_o and [Na⁺]_o on both transient and steady-state ouabain-sensitive current. At alkaline or neutral pH_o the relaxation rate of pre-steady-state current is an exponential function of voltage. Its U-shaped voltage dependence becomes apparent at acidic pH_o, as predicted by a model in which protonation of the Na⁺/K⁺ pump reduces the energy barrier between the internal solution and the Na⁺ occluded state. The model also predicts that acidic pH_o increases steady-state current leak through the pump. The apparent pK of the titratable group(s) is 6, suggesting that histidine is involved in induction of the conductance pathway. ²²Na efflux experiments in squid giant axon and current measurements in oocytes at acidic pH_o suggest that both Na⁺ and H⁺ are permeant. The acid-induced inward current is reduced by high [Na⁺]_o, consistent with block by Na⁺. A least squares analysis predicts that H⁺ is four orders of magnitude more permeant than Na⁺, and that block occurs when 3 Na⁺ ions occupy a low affinity binding site (K _0.5=130±30 mM) with a dielectric coefficient of 0.23±0.03. These data support the conclusion that the ouabain-sensitive conducting pathway is a result of passive leak of both Na⁺ and H⁺ through the Na⁺/K⁺ pump.     

Regulation of rRNA gene number in Drosophila melanogaster: new aspects resulting from the use of free duplications

Summary We have isolated a bobbed (bb) mutant on the free duplication Dp(1; f)122bb ⁺ and we have measured the rDNA content of the bb ⁺ and the bb loci in genetic combinations in which none of the phenomena involved in the change of the rDNA redundancy occurs. We have also measured the rDNA content of the two bb loci carried by the free duplications in two different genetic combinations: (1) and females in which there are two attached X chromosomes completely deleted for the nucleolus organizer (NO) regions and there-fore the only rDNA is contributed by the free duplication; (2) X/Dp122bb ⁺ and X/Dp122bb males, in which there are two bb loci, one on the X chromosome and the other on the X free duplication.The bb ⁺ and the bb duplications produced an overall increase of the rDNA content in the two genetic conditions tested.These results are not in favour of both a cis and trans effect of the regulator locus (cr ⁺ locus) hypothesised as being involved in the disproportionate replication of rRNA genes.     

Solution conformations of proline rings in proteins studied by NMR spectroscopy

Summary Three different conformations of proline rings in a protein in solution, Up, Down and Twist, have been distinguished, and stereospecific assignments of the pyrrolidine -, - and -hydrogens have been made on the basis of ¹H-¹H vicinal coupling constant patterns and intraresidue NOEs. For all three conformations, interhydrogen distances in the pairs -³, ³-³, ²-², ²-², and ³-³ (2.3 Å) are shorter than those in the pairs -², ²-³, ³-², ²-³, and ³-² (2.7–3.0 Å), resulting in stronger NOESY cross peaks. For the Up conformation, the ³-² and ²-³ spin-spin coupling constants are small (<3 Hz), and weak cross peaks are obtained in a short-mixing-time (10 ms) TOCSY spectrum; all other vicinal coupling constants are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. For the Down form, the -², ²-³, and ³-² vicinal coupling constants are small, leading to weak TOCSY cross peaks; all other couplings again are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. In the case of a Twist conformation, dynamically averaged coupling constants are anticipated. The procedure has been applied to bovine pancreatic trypsin inhibitor and Cucurbita maxima trypsin inhibitor-V, and ring conformations of all prolines in the two proteins have been determined.     

Peripheral Pool of CD8+ T-Cells Contains Lymphocytes with Antigen-Specific Receptors That Recognize Syngeneic MHC Class II Molecules

The capacity of T-lymphocytes to recognize nonself and tolerating self is formed as a result of positive and negative selection in the thymus. While obtaining and testing specificity of T-hybridomas, we demonstrated that the major part of peripheral pool of CD⁸⁺ T-lymphocytes carried receptors specific to self MHC class II molecules. Such an unexpected specificity of receptors has been found in some T-cell hybridomas produced by fusion of activated peripheral CD8⁺ T-lymphocytes with a tumor partner transfected by the coreceptor CD4 gene. The reactivity to self is not an experimental artifact due to an increased avidity of interaction of the hybridoma cells with antigen-presenting cells. Also, it is not an expression of reactivity of T-cells to superantigens, products of endogenous viruses of mouse breast cancer. The formation of a pool of such T-cells involves both cells with double receptor specificity and cells coexpressing two -chains of T-cell receptor. Their appearance in the periphery can be due to the capacity of thymocytes differentiating in the direction of CD4⁺ cells to avoid negative selection via change of expression of coreceptor CD4 to CD8.     

A K+-selective,three-state channel from fragmented sarcoplasmic reticulum of frog leg muscle

Summary Sarcoplasmic reticulum (SR) vesicles from frog leg muscle were fused with a planar phospholipid bilayer by a method described previously for rabbit SR. As a result of the fusion, K⁺-selective conduction channels are inserted into the bilayer. Unlike the two-state rabbit channel, the frog channel displays three states: a nonconducting (closed) state and two conducting states and . In 0.1m K⁺ the single-channel conductances are 50 and 150 pS for and , respectively. The probabilities of appearearance of the three states are voltage-dependent, and transitions between the closed and states proceed through the state. Both open states follow a quantitatively identical selectivity sequence in channel conductance: K⁺>NH ₄ ⁺ >Rb⁺>Na⁺>Li⁺>Cs⁺. Both open states are blocked by Cs⁺ asymmetrically in a voltage-dependent manner. The zero-voltage dissociation constant for blocking is the same for both open states, but the voltage-dependences of the Cs⁺ block for the two states differ in a way suggesting that the Cs⁺ blocking site is located more deeply inside the membrane in the than in the state.     

Relationship of the Donnan potential to the transmembrane pH gradient in tracheal apical membrane vesicles

Summary Experiments were performed to determine the factors which contribute to the transmembrane pH gradient (pH) and the potential gradient () in apical plasma membrane vesicles isolated from bovine tracheal epithelium. As indicated by the accumulation of¹⁴C-methylamine, the vesicles maintained a pH (inside acidic) which was dependent upon the external pH. The pH was also proportional to the ionic strength of the suspending medium, suggesting that the H⁺ distribution was dictated by a Donnan potential. Measurements of the distribution of⁸⁶Rb⁺ demonstrated an electrical potential gradient across the vesicle membrane, inside negative which was proportional to the medium ionic strength. pH changed in parallel with in response to a variety of imposed conditions. These results are compatible with the existence of a H⁺ conductance in the vesicle membrane. Thus the endogenous electrical and proton gradients may be manipulated and used as a general experimental tool to complement kinetic analysis in investigations of transport mechanism using isolated vesicle preparations.     

A re-examination of the Na+-independent binding of [3H]β-alanine to rat brain stem-spinal cord

The Na⁺-independent binding of [³H]-alanine to rat brain stem plus spinal cord was reinvestigated, in order to study in more detail the characteristics of previously described -alanine binding processes. Binding was absent when amino acid-free postnuclear supernatants or crude synaptic membranes were used. Experiments performed with several other Na⁺-free preparations showed a sole binding component, irrespective of the preparation used. Biochemical characterization of this Na⁺-independent binding, using frozen/thawed/washed synaptosomal-mitochodrial fractions, showed that binding reached a plateau between 7 min and 13 min, increasing thereafter. Binding was linear with fraction protein over a range of 200–415 g/ml incubation medium. Binding was completely inhibited by glycine, alanine, -aminobutyric acid, -aminoisobutyric acid, hypotaurine and strychnine, and to a lesser extent by 2,2-dimethyl--alanine, brucine and gelsemine. It was insensitive to taurine, -aminobutyric acid (GABA), 2-guanidinoethanesulfonic acid (GES), carnosine, and bicuculline methiodide. Binding was reversible, saturable (K _D 20 M), and heat sensitive.     

Mutants in yeast affecting ethidium bromide induced rho- formation and their effects on transmission and recombination of mitochondrial genes.

Summary A series of mutants called ebi, less inducible by ethidium bromide than the parental strain for the ^+– mutation have been isolated after E.M.S. mutagenesis. Some of the ebi mutants also show an important accumulation of ^– cells, in the absence of ethidium bromide. Ebi mutations are nuclearly inherited as shown by meiotic segregation. The effects of these mutants on the transmission and recombination of mitochondrial genes among the diploid progeny of crosses have been studied. Some of the ebi mutants show a non coordinated transmission of the oli1 mitochondrial marker with respect to other mitochondrial markers unexpected for homosexual crosses. This bias which is independent from will be discussed in relation to the segregation and recombination. No significant decrease of the frequency of recombinants has been detected.Abbreviations E.B. Ethidium bromide - E.M.S. Ethyl méthane sulfonate - C^S/C^R Allelic forms of the rib 1 locus conferring chloramphenicol sensitivity/resistance - E^S/E^R Allelic forms of the rib 3 locus conferring erythromycine sensitivity/resistance - O^R/O^R Allelic forms of the oli 1 locus conferring oligomycin sensitivity/resistance - P^S/P^R Allelic forms of the par 1 locus conferring paromomycine sensitivity/resistance - D^S/D^R Allelic forms of the diu 1 or diu 2 loci conferring diuron sensitivity/resistance - C^S/C^R Allelic forms of the mitochondrial locus - ⁺ grande or respiratory competent cells - ^– petite or cytoplasmic respiratory deficient cells     

Significance of the β-Subunit in the Biogenesis of Na+/K+-ATPase

This review summarizes our experiments on the significance of the -subunit in the functional expression of Na⁺/K⁺-ATPase. The -subunit acts like a receptor for the -subunit in the biogenesis of Na⁺/K⁺-ATPase and facilitates the correct folding of the -subunit in the membrane. The -subunit synthesized in the absence of the -subunit is subjected to rapid degradation in the endoplasmic reticulum. Several assembly sites are assigned in the sequence of the -subunit from the cytoplasmic NH₂-terminal domain to the extracellular COOH-terminus: the NH₂-terminal region of the extracellular domain, the conservative proline in the third disulfide loop, the hydrophobic amino acid residues near the COOH-terminus and the cysteine residues forming the second and the third disulfide bridges. Upon assembly, the -subunit confers a resistance to trypsin on the -subunit. The conformations induced in the -subunit of Na⁺/K⁺-ATPase by Na⁺/K⁺- and H⁺/K⁺-ATPase -subunits are somehow different from each other and are named the NK-type and KH-type, respectively. The extracellular domain of the -subunit is involved in the folding of the -subunit leading to trypsin-resistant conformations. The sequences from Cys150 to the COOH-terminus of the Na⁺/K⁺-ATPase -subunit and from Ile89 to the COOH–terminus of the H⁺/K⁺-ATPase -subunit are necessary to form trypsin-resistant conformations of the NK- and HK-type. respectively. The first disulfide loop of the extracellular domain of the -subunits is critical in the expression of functional Na⁺/K⁺-ATPase.     

Conformational transmission in ATP synthase during catalysis: Search for large structural changes

Escherichia coli ATP synthase has eight subunits and functions through transmission of conformational changes between subunits. Defective mutation at Gly-149 was suppressed by the second mutations at the outer surface of the subunit, indicating that the defect by the first mutation was suppressed by the second mutation through long range conformation transmission. Extensive mutant/pseudorevertant studies revealed that / and / subunits interactions are important for the energy coupling between catalysis and H⁺ translocation. In addition, long range interaction between amino and carboxyl terminal regions of the subunit has a critical role(s) for energy coupling. These results suggest that the dynamic conformation change and its transmission are essential for ATP synthase.     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

13Cα and 13Cβ chemical shifts as a tool to delineate β-hairpin structures in peptides

Unravelling the factors that contribute to the formation and the stability of -sheet structure in peptides is a subject of great current interest. A -hairpin, the smallest -sheet motif, consists of two antiparallel hydrogen-bonded -strands linked by a loop region. We have performed a statistical analysis on protein -hairpins showing that the most abundant types of -hairpins, 2:2, 3:5 and 4:4, have characteristic patterns of ¹³C and ¹³C conformational shifts, as expected on the basis of their and angles. This fact strongly supports the potential value of ¹³C and ¹³C conformational shifts as a means to identify -hairpin motifs in peptides. Their usefulness was confirmed by analysing the patterns of ¹³C and ¹³C conformational shifts in 13 short peptides, 10–15 residues long, that adopt -hairpin structures in aqueous solution. Furthermore, we have investigated their potential as a method to quantify -hairpin populations in peptides.     

Active transport in phototrophic bacteria

Phototrophic bacteria utilize light-driven, cyclic electron flow to pump protons out of their cytoplasm, creating an electrochemical proton gradient, _H+, outside acid and positive. These bacteria exchange external protons for internal cations (Na⁺, K⁺ and Ca⁺²), allowing the cells to maintain a nearly constant internal pH while maintaining the electrical component of _H+. Na⁺/H⁺ exchange also establishes an electrochemical Na⁺ gradient. Phototrophic bacteria are able to utilize these electrochemical gradients as energy sources for the uptake of a wide variety of metabolites (e.g., sugars, organic acids and amino acids) via metabolite/cation symports.     

Ibf-1 (Iodine binding factor), a highly variable marker system in the Triticeae

Summary Isoelectric focusing of extracts from the endosperm of mature grains of hexaploid wheat and related species was used to study the genetic control of Iodine binding factor (IBF). Ten IBF bands were present in Chinese Spring (CS) and analysis of the nullisomictetrasomic and ditelosomic lines of CS showed nine of them to be controlled by genes on the long arms of the homoeologous group 5 chromosomes. Five alleles were detected at Ibf-A1 locus, four at Ibf-B1 and four at Ibf-D1 among a sample of 46 wheat genotypes. Homoeoloci were found on chromosome 5R of Secale cereale, 5E of Agropyron elongatum, 5U of Aegilops umbellulata, 5Agⁱ of Agropyron intermedium, 5S¹ and 4S¹ of Aegilops sharonensis and 4H of Hordeum vulgare.     

Axillary shoot induction and plant regeneration in Plantago ovata Forssk

Axillary shoot induction and plant regeneration were obtained in Plantago ovata. The optimum medium for inducing axillary shoots was Murashige & Skoog (MS) medium [5] supplemented with 4.6 M kinetin and 0.05 M NAA. Rooting of shoots was best on half-strength MS medium containing 5.0 M IBA and 0.05 M kinetin. The regenerated plants were similar to the control plants in karyotypic and phenotypic details.