Photomodification of Cardiac Membrane: Chaotic Currents and High Conductance States in Isolated Patches

We have demonstrated previously that photomodification permeabilizes cardiac cells as evidenced by activation of a whole-cell leak current. In this paper we report that photomodification induces in cell-attached and inside-out cardiac membrane patches a chaotic current. Unlike current recordings from many protein ion channels that show stepwise amplitude changes associated with open and closed states of the channel, the chaotic current consists of variable amplitude spike-like transitions. The amplitudes of these spikes can vary from tenths to tens of picoamperes at a constant transmembrane potential. We provide evidence that the chaotic current is transmembrane rather than trans-seal and has a voltage dependency expected for current flow through nonspecific conductance pathways. Photomodification can also induce high conductance states (greater than 500 pS) in cell-attached and inside-out patches. We present evidence that the high conductance state is also not related to seal breakdown. Our results suggest that both the chaotic current activity in and high conductance state of photo-modified cardiac membrane patches result from the opening of many small conductance, nonspecific pathways through the membrane.     

The structure and chemistry of ethylene adsorbed on platinum (111): CFSO-BEBO calculations and experimental studies

The structure and chemistry of ethylene adsorbed on a platinum (111) surface has been studied. Ethylene adsorbs irreversibly and dissociatively with unity sticking coefficient in the first monolayer, which is ordered in a (2 × 2) array. A second monolayer in registry with the first is adsorbed reversibly. Self-hydrogenation takes place during dynamic adsorption-desorption which poisons the reversible adsorptivity. The reversibly-held ethylene desorbs at the lowest temperatures (E_d = 25 kcal) followed by dissociated hydrogen (E_d = 30 kcal) and the decomposition of hydrogen in the acetylenic first monolayer (E_d = 38 kcal). Residual carbon coalesces to graphite at temperatures in excess of 500°C. CFSO-BEBO calculations qualitatively predict all of the binding states observed. Treating PtC valency as a single adjustable parameter, all four binding energies and four of the five activation energies are in quantitative agreement with experiment.     

On functions that are trivial cocycles for a set of irrationals. II

Two results are obtained about the topological size of the set of irrationals for which a given function is a trivial cocycle. An example of a continuous function which is a coboundary with non- cobounding function is constructed.

     

Chemistry of thienopyridines. XIX. Further studies on chlorination and S-oxidation in the thieno[2,3-b] pyridine system

Treatment of thieno [2,3-b] pyridine (1a) with chlorine gas in chloroform (plus water) gave a mixture of two 2,3-dichloro-2,3-dihydrothieno[2,3-b] pyridine 1-oxides [trans-syn (IIa), and cis-anti (IIb)) [and 2,3,3-trichloro-2,3-dihydrothieno[2,3-b]pyridine syn-1-oxide (IVa), as well as a non-isolated fourth product (prohably the anti isomer of IVa) and sometimes a small amount of thieno[2,3-b]pyridine 1,1-dioxide (III). Treatment of Ia in a solvent (water, chloroform-water, or THF-water) with sulfuric acid and sodium hypochlorite gave a mixture of IIb and III. Effects of variations of reaction conditions on the composition of the product mixture were ascertained through chemical isolation and/or pmr analysis. Products formed were rationalized in terms of the chlorine-water-hypochlorous acid equilibrium, plus attack of chlorine variously at positions 1 (S-atom), 2, and 3 of 1a, but of hypochlorous acid only at position 1. Thermal and chromatographic limitations on isolation procedures for some of the products were established. Stereochemistries of IIa, IIb, and IVa were assigned by means of pmr spectrometry with the aid of the shift reagent Eu(fod)₃. Spin-spin couplings between the proton at position 2 and those at positions 4 and 6 were observed at high resolution. In exploratory runs, 5-ethyl-la was converted into isolable 2,3-dichloro-5-ethyl-2,3-dihydrothieno[2,3-b]pyridine 1-oxide, and 5-acetyl-Ia yielded 3-chloro-5-acetylthieno] 2,3-b]pyridine. Mass spectral fragmentation patterns for the various products are presented.     

GH3 Cells, Ionic Currents and Cell Killing: Photomodification Sensitized by Rose Bengal

Photosensitization using Rose Bengal (RB) modifies membrane ionic currents and kills cultured mouse pituitary, GH₃, cells. Here we investigate the dose-response relationship for ionic current modification and for cell killing to assess a possible causal link. When exposed to 0.5 μM RB and 6.5 mW/cm² of visible light, calcium current was blocked in 1.9 ± 0.2 min (meanSEM; 0.74 ± 0.08 J/ cm²; n = 18), a transient component of potassium current, tentatively identified as a delayed-rectifier potassium current, disappeared in 52 ± 8 s (0.34 ± 0.05 J/cm²; n = 10) and a steady-state component of potassium current, largely a calcium-activated potassium current, disappeared in 3.5 ± 0.4 min (1.37 ± 0.16 J/cm²; n = 11). Conversely, the background leak current increased in magnitude. At 5 min of illumination, the longest time studied here, it continued to increase nearly linearly, making it the only current component studied that is still changing after 5 min of light. Under the conditions used, cell killing increased to 100% in the exposure range of4–10 min of illumination (1.6 J/cm² to 3.9 J/cm²) when assessed using fluorescent markers, ethidium homodimer and calcein and required slightly longer exposure times when assessed using trypan blue. Thus, it is difficult to ascribe a causal role in cell killing by photosensitization to alterations of standard ion channels and known ionic currents. However, the increase in leak current has the correct dose-response characteristics to be involved.     

Modification of an epichlorohydrin polymerization

The acid-catalyzed polymerization of epichlorohydrin was modified by the addition of 1,4-butanediol diglycidyl ether to the reaction. The amount of diepoxide added and the method of addition were varied to produce a series of polymers with increased molecular weight, broad molecular weight distributions, and variations in hydroxyl functionality. Polyurethane networks were prepared from these polyols for the evaluation of elastomeric properties. The most obvious result was the lack of elastomeric network formation in the unmodified material when modified polyols produced elastomeric properties under the same conditions. Differences in properties between samples with more diepoxide added in the original polymerization generally showed trends to lower elongation and higher modulus. Changes in the method of addition of the diepoxide produced great differences in the toughness of the elastomers formed in the cure process.     

Equilibration studies of an inorganic ion exchange material with liquid nuclear waste simulant using radiotracer techniques

Ion exchange distribution coefficients of zirconium, ruthenium, europium, and strontium, elements found in high level nuclear waste, were determined for a new titanium hydrous oxide-type inorganic ion exchange compound. Coefficients were determined at ambient temperatures and at 85°C. The equilibrations were done in solutions simulating the composition of nuclear waste expected from the Allied-General Nuclear services, Barnwell. South Carolina plant. The progress of each reaction was monitored by adding a radiotracer of the element investigated to the simulated waste solution. Ambient temperature distribution coefficients ranging from a high of 1.2·10⁶ for Zr to a low of 58 for Eu were obtained when equal weights of ion exchange material were used. Significantly higher distribution coefficients were found at 85°C than at ambient temperatures. This work was supported by the U. S. Energy Research Development Administration.     

Chemistry of thienopyridines. XIII. Selective formation of sulfones in Bi- and tricyclic Systems. Thieno[2,3-b]pyridine 1,1-dioxide as a dienophile

Bicyclic and tricyclic thienopyridines are converted into sulfones in 13-73% yield by means of acid-hypochlorite. The sulfone thieno[2,3-b]pyridine 1,1-oxide (Ib) undergoes Diels-Alder condensation with furan (both exo and endo products formed), anthracene, and naphthacene. Self-condensation of Ib occurs with elimination of sulfur dioxide to give 8-(3-pyridyl)quinoline (XV). The structure of XV was established by means of pmr and a europium shift reagent. Ultraviolet, pmr, and mass spectral data for various compounds are presented and discussed.     

Chemistry of thienopyridines. XII. Selective formation of N-oxides,sulfoxides, and sulfones in some tricyclic systems

Direct conversion of [1]benzothieno[3,2-b]pyridine (IVa), thieno[3,2-b:4,5-b']dipyridine (Va), and thieno[2,3-b:4,5-b']dipyridine (VIa) into their sulfoxides was effected by means of an equimolar quantity of iodobenzene dichloride in aqueous acetonitrile. Treatment of IVa-VIa with excess chlorine gas in carbon tetrachloride and then with water gave the corresponding sulfones, IVc-VIc. Hydrogen peroxide in glacial acetic acid converted Va and VIa into di-N-oxides, thieno[3,2-b]pyridine into its N-oxide, and sulfone VIc into an N-oxide sulfone (X). Spectral and chemical means of distinguishing amongst the oxide functions are noted, and rationalizations for selectivity in the oxidations are discussed.