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PubMed1988

Electrogenic ATP-dependent Cl- transport by plasma membrane vesicles from Aplysia intestine.

A Cl--stimulated adenosinetriphosphatase (ATPase) activity and an ATP-dependent Cl- transport process were found in Aplysia enterocyte plasma membranes. In an attempt to further elucidate this transport process plasma membrane vesicles from Aplysia enterocytes were prepared utilizing differential centrifugation and sucrose density gradient techniques. Electrogenicity of the ATP-dependent Cl- transport was confirmed in three ways. First, an inwardly directed valinomycin-induced K+ diffusion potential, making the vesicle interior electrically positive, enhanced ATP-driven Cl- uptake compared with vesicles lacking the ionophore. Second, ATP plus Cl- increased intravesicular negativity measured by lipophilic triphenylmethylphosphonium distribution across the vesicular membrane. Third, both vanadate and thiocyanate inhibited the ATP plus Cl--dependent intravesicular negativity. These results are consistent with the hypothesis that the active electrogenic Cl- transport mechanism in Aplysia intestine could be a Cl--stimulated ATPase found in the enterocyte plasma membrane.

Adenosine Triphosphate↗
PubMedDate not supplied

Defective function of membrane potential (psi) on sperm of infertile men.

Membrane potential across the plasma membrane (psi) of human sperm was determined by measuring the accumulation of triphenylmethylphosphonium (TPMP+). Washed sperm of fertile or infertile men were suspended, incubated in low-K+ and high-Na+ or high-K+ and low-Na+ medium, and allowed to take up the cation TPMP+ to a steady state (20 min at 37 degrees C). Under these conditions a psi of -75 +/- 6 mV was observed in sperm cells of fertile men, while in spermatozoa of idiopathic and asthenozoospermic infertile men, the psi was of 35 +/- 5 mV and 32 +/- 5 mV, respectively. Upon depolarization of the sperm membrane by K+, the transport system Na(+)-K+ in spermatozoa of idiopathic infertile men decreased 53 +/- 3.5%, while that in sperm cells asthenozoospermic men decreased 57 +/- 3% with respect to spermatozoa of fertile men. The results of these studies indicate their possible application to the diagnosis of male infertility.

Humans↗
PubMed1983

Triphenylmethylphosphonium (TPMP+) as a probe for peritubular membrane potential in the kidney slice.

The present work was undertaken to assess the validity of the use of TPMP+, a lipophilic cation, as a basolateral membrane-potential probe in the rabbit kidney slice. Cortical slices incubated in media containing 3H-TPMP+ reached an equilibrium slice/medium concentration ratio (S/M) for TPMP+ after 90 min. The equilibrium S/M TPMP+ was approximately 20 at TPMP+ concentrations between 30 and 50 microM. Concentrations of TPMP+ above 50 microM resulted in changes in tissue electrolytes and O2 consumption. Anaerobic incubation of slices in the presence of iodoacetamide decreased the S/M TPMP to approximately 3. When medium K+ was progressively increased, the S/M TPMP+ decreased continuously. There was a linear correlation between cell water/medium concentration ratios (C/M) for TPMP+ and K+ (r = 0.629, P less than 0.01). However, the C/M TPMP+ was 29.0 even at C/M K+ of 1.0, strongly suggesting the presence of a tissue binding component for TPMP+. When corrections are made for the above binding, the average C/M TPMP+ in slices incubated in the normal medium was approximately 13, equivalent to a Nernst potential of -64 mV. This value compared favorably to -54.3 mV obtained by microelectrodes in slices treated in the same fashion. It is concluded that the C/M TPMP+ corrected for binding may be used as a measure of the basolateral membrane potential in the steady state.

Animals↗
PubMedDate not supplied

Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study.

PURPOSE: The purpose of this study was to determine the fracture resistance of three-unit fixed partial dentures (FPD) made of new core ceramics. MATERIALS AND METHODS: A base metal three-unit master FPD model with a maxillary premolar and molar abutment was made. Tooth preparation showed 0.8-mm circumferential and 1.5-mm occlusal reduction and a chamfer margin design. FPDs were constructed with a uniform 0.8-mm-thick core ceramic and a porcelain veneer layer. In-Ceram Alumina, In-Ceram Zirconia, and DC-Zirkon core ceramics were machined by a computer-aided design/manufacturing system, whereas IPS Empress 2 core ceramic was indirectly built up using the fabrication technology of waxing and heat pressing. FPDs of IPS Empress were heat pressed as complete restorations without core material. To ensure standardized dimensions, the FPDs were controlled at different points. All FPDs were cemented with ZnPO4 on the master model and loaded on a universal testing machine until failure. The failure load and mode of failure were recorded. RESULTS: The highest failure loads, exceeding 2,000 N, were associated with FPDs of DC-Zirkon. FPDs of IPS Empress and In-Ceram Alumina showed the lowest failure loads, below 1,000 N, whereas intermediate values were observed for FPDs of IPS Empress 2 and In-Ceram Zirconia. Differences in mean values were statistically significant. CONCLUSION: The high fracture resistance evaluated for FPDs made of DC-Zirkon underscores the remarkable mechanical properties of high-performance ceramic, which could be useful for highly loaded all-ceramic restorations, especially in the molar region.

Aluminum Oxide↗
PubMed2001

Carbonates, thiocarbonates, and the corresponding monoalkyl derivatives. 1. Their preparation and isotropic (13)C NMR chemical shifts.

Three series of potassium carbonate and thiocarbonate salts were synthesized, and the corresponding (13)C isotropic solid-state NMR and the aqueous solution (13)C and (1)H NMR data were collected. The series of compounds that were studied consists of (1) the parent compounds, i.e., potassium carbonate, K(2)CO(3), potassium hydrogen carbonate, KHCO(3), potassium monothiocarbonate, K(2)CO(2)S, potassium dithiocarbonate, K(2)COS(2), and potassium trithiocarbonate, K(2)CS(3), (2) the oxygen monoalkyl substituted derivatives of the parent compounds (OR series), i.e., three potassium O-alkylcarbonates, KO(2)COR, three potassium O-alkylmonothiocarbonates, KOSCOR, and three potassium O-alkyldithiocarbonates, KS(2)COR, all with R = CH(3), CH(2)CH(3), CH(CH(3))(2), and (3) the sulfur monoalkyl substituted derivatives of the parent compounds (SR series), i.e., two potassium S-alkylmonothiocarbonates, KO(2)CSR; two potassium S-alkyldithiocarbonates, KOSCSR, and two potassium S-alkyltrithiocarbonates, KS(2)CSR, all with R = CH(3) or CH(2)CH(3). The preparation and proper characterization of KO(2)CSR and KOSCSR with R = CH(3) and CH(2)CH(3) along with new IR and X-ray powder diffraction data for several other compounds in the series are reported for the first time in this study. Solution NMR data for KO(2)CSR (R = CH(3), CH(2)CH(3)) and KOSCSR (R = CH(3)) and solid-state NMR data for K(2)CO(2)S and K(2)COS(2) could not be obtained because they are unstable under the corresponding measurement conditions. The isotropic chemical shift values of the central carbon atoms obtained from solid-state MAS (magic angle spinning) NMR experiments deviate at most by 3 ppm from the corresponding solution values. Two major trends in the (13)C chemical shift values of the central carbon atoms were found. First, if an oxygen atom in a parent compound or in an alkyl-substituted derivative is replaced by a sulfur atom, a significantly higher chemical shift value is observed. This trend is discussed in terms of the paramagnetic contribution to the chemical shielding constant. Second, the size of the alkyl group in the monoalkyl derivatives has a very small effect on the chemical shift values of the central carbon atoms. This observation is explained using the concept of varying inductive effects produced by alkyl groups. The trends observed for the (13)C and (1)H chemical shift values of the alkyl groups follow common concepts on the structure dependency of chemical shifts.

Journal Article↗
PubMed1984

Cellular membrane contrast and contrast differentiation with osmium triazole and tetrazole complexes.

Addition of heterocyclic nitrogen compounds to the classical osmium tetroxide postfixation medium, applied after glutaraldehyde fixation, results in enhanced membrane contrast in ultrathin sections of liver tissue. The addition of similar compounds to potassium osmate solutions, results in contrast differences in some cellular membranes. The membranes of the rough endoplasmic reticulum, the nuclear envelope and the plasma membrane acquire contrast, while the mitochondrial membranes do not. The apolar regions of membranes are contrasted when osmium tetroxide is combined with heterocyclic nitrogen compounds, whereas the polar regions are contrasted by combinations of potassium osmate with these compounds. This polar membrane contrast is probably due to the presence of an amino-group in the heterocyclic nitrogen compounds. Compounds without the amino-group do not contrast membranes, although the glycogen is contrasted. X-ray microanalysis served to establish the relative osmium content in contrasted glycogen, and showed that such nitrogen compounds play a role in complexation of cations in aldehyde-fixed tissues. Electron spectroscopy for chemical analysis (ESCA) measurements of isolated muscle glycogen show that after treatment with various osmium tetroxide or potassium osmate solutions, hexavalent and quadrivalent osmium species are present in the glycogen. The presence of (heterocyclic) nitrogen compounds in such solutions stabilizes certain osmium valency species, and this may account for the contrast observed.

Amitrole↗
PubMed1989

[Synthesis of 3-cyano-6-methyl-4-pyridyl-2(1H)-pyridinethiones as well as 2-substituted 6-methyl-4-pyridyl-pyridine-3-carbonitriles and 3-carbonic acid amides, respectively, and testing their cardiovascular activity].

By the base catalyzed reaction of our previously described 3-cyano-6-methyl-4-pyridyl-2(1H)-pyridinethiones 1 and 2, respectively, with branched and unbranched, respectively, alkyl, aralkyl-, alkinyl-, hydroxyalkyl-, ethoxycarbonyl- and carbamoylalkylhalides the new in 2-position substituted 6-methyl-4-pyridyl-pyridine-3-carbonitriles 15-30 were formed. By means of oxidation of the 2-methylthio-substituted pyridine-3-carbonitriles 3 and 4 with potassium periodate and potassium permanganate in diluted acetic acid, respectively, the sulfinyl compounds 5 and 6, respectively, and the sulfonyl compounds 7 and 8, respectively, were prepared. By heating of 3 and 4, respectively, with concentrated sulphuric acid the 2-methylthio-pyridine-3-carboxamides 9 and 10 were obtained. The oxidation of these compounds with potassium periodate and potassium permanganate, respectively, had yield the pyridines 11 and 12, respectively, as well as 13 and 14, respectively.

Amides↗
PubMed2007

Discovering potassium channel blockers from synthetic compound database by using structure-based virtual screening in conjunction with electrophysiological assay.

Potassium ion (K+) channels are attractive targets for drug discovery because of the essential roles played in biological systems. However, high-throughput screening (HTS) cannot be used to screen K+ channel blockers. To overcome this disadvantage of HTS, we have developed a virtual screening approach for discovering novel blockers of K+ channels. On the basis of a three-dimensional model of the eukaryotic K+ channels, molecular docking-based virtual screening was employed to search the chemical database MDL Available Chemicals Directory (ACD). Compounds were ranked according to their relative binding energy, favorable shape complementarity, and potential to form hydrogen bonds with the outer mouth of the K+ channel model. Twenty candidate compounds selected from the virtual screening were examined using the whole-cell voltage-clamp recording in rat dissociated hippocampal neurons. Among them, six compounds (5, 6, 8, 18-20) potently blocked both the delayed rectifier (IK) and fast transient K+ currents (IA). When applied externally, these six compounds preferentially blocked IK with potencies 2- to 500-fold higher than that of tetraethylammonium chloride. Intracellular application of the six compounds had no effect on both K+ currents. In addition, the interaction models and binding free energy calculations demonstrated that hydrophobic interaction and solvent effects play important roles in the inhibitory activities of these compounds. The results demonstrated that structure-based computer screening strategy could be used to identify novel, structurally diverse compounds targeting the pore binding pocket of the outer mouth of voltage-gated K+ channels. This study provides an alternative way of finding new blockers of voltage-gated K+ channels, while the techniques for high-throughput screening of K+ channel drugs remain in development.

Animals↗