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PubMed2005

Synthesis and characterization of the open-framework barium bisphosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O.

Following the strategy of using polyfunctional phosphonic acids for the synthesis of open-framework metal phosphonates, the phosphonocarboxylic acid (H2O3PCH2)2NCH2C6H4COOH was used in the hydrothermal synthesis of new Ba phosphonates. Its decomposition led to the first open-framework barium phosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O. The synthesis was also successfully performed using iminobis(methylphosphonic acid), (H2O3PCH2)2NH, as a starting material, and the synthesis was optimized to obtain as a pure material. The reaction setup as well as the pH are the dominant parameters, and only a diffusion-controlled reaction led to the desired compound. The crystal structure was solved from single-crystal data: monoclinic; C2/c; a=2328.7(2), b=1359.95(7), and c=718.62(6) pm; beta=98.732(10) degrees ; V=2249.5(3)x10(6) pm3; Z=4; R1=0.036; and wR2=0.072 (all data). The structure of [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O is built up from BaO8 and BaO10 polyhedra forming BaO chains and layers, respectively. These are connected to a three-dimensional metal-oxygen-metal framework with the iminobis(methylphosphonic acid) formally coating the inner walls of the pores. The one-dimensional pores (3.6x4 A) are filled with H2O molecules that can be thermally removed. Thermogravimetric investigations and temperature-dependent X-ray powder diffraction demonstrate the stability of the crystal structure up to 240 degrees C. The uptake of N,N-dimethylformamide and H2O by dehydrated samples is demonstrated. Furthermore, IR, Raman, and 31P magic-angle-spinning NMR data are also presented.

Journal Article↗
PubMed1975

Induction of a myogenic response in tonic airway smooth muscle by tetraethylammonium.

In multi-unit tracheal smooth muscle (TSM), quick stretches applied at a velocity of 5 times the measured maximum velocity of isotonic shortening of the muscle, of a magnitude 3 times the measured extension of the series-elastic component when the muscle contracts maximally, and at optimal muscle length (L-o) were unable to elicit any myogenic response (MR). Experimental conditions such as hypoxia (P-O2 smaller than 60 mmHg) and acidosis (pH equals 6.8) or the presence of Ba2+ (2 mM), acetylcholine (10-6 M), or high (K+)-o (59 mM) were also unable to elicit the MR. However, tetraethylammonium chloride (TEA, 0.4-67 mM) produces 1) spontaneous phasic contractions and 2) a MR to quick stretch. The ionic basis for these changes was then investigated by studying the Ca and Mg dependence of the response to TEA. The dose-response relationship to TEA was shifted to the left by decreasing external Mg2+ from 2.5 to 0.5 mM. The ability of TSM to produce a MR was absolutely dependent on external Ca, but the threshold concentration required shifted from 2.5 times 10-5 M at normal external Mg (2.5 mM) to 5 times 10-4 M at the reduced external Mg (0.5 mM). The effects of TEA on spontaneity and the MR were abolished by D-600. These results suggest that 1) TEA functionally converts multiunit smooth muscle into a single unit one and leads to the development of a MR and 2) the MR results from a depolarization-activated mobilization of Ca and is inhibited by ionic conditions known to increase membrane permeability.

Acetylcholine↗
PubMed1979

Dagnostic imaging of the upper part of the abdomen.

The new diagnostic procedures developed during the last several years present a confusing dilemma. The state of the art of ultrasound, computed tomography and nuclear scintigraphy is progressing so rapidly that what one says today is generally out of date tomorrow. However, certain guidelines should be followed in evaluating various organ systems. Generally, ultrasound is the procedure of choice in the upper part of the abdomen in most patients who are not extremely obese or filled with intestinal gas. A sonogram is less expensive than computed tomography and, at the present time, is considered noninvasive compared with compound tomography, which produces a small, but significant, radiation exposure. The accuracy of the two modalities is quite similar. Using the slight advantage that computed tomography may have in a given organ system does not generally override other factors, such as cost and radiation dose. However, mitigating factors, such as obesity, presence or absence of intestinal gas or barium, should be taken into account when selecting patients for either procedure. In many clinical situations, neither computed tomography nor ultrasound should be used until other modalities, such as conventional radiography or scintigraphy, have first been tried. Should the problem not be resolved by these more conventional techniques, an ultrasound or computer tomographic examination may be indicated to delineate further the pathologic condition of the abdomen.

Abdomen↗
PubMed2003

Pharmacological effects of (+)-nantenine, an alkaloid isolated from Platycapnos spicata, in several rat isolated tissues.

In this work, the potential activity of (+)-nantenine (a natural aporphin alkaloid) in several rat isolated tissues was studied. In rat isolated intact aorta, (+)-nantenine (0.05 - 0.5 microM) competitively antagonized with almost equal effectiveness the contractions produced by phenylephrine (PE) and 5-hydroxytryptamine (5-HT) in normal Krebs solution. However, at higher concentrations (2 microM), the alkaloid also reduced the maximal effect induced by these two agonists. In depolarizing Ca2+-free high KCl 50 mM solution, (+)-nantenine (1.5 - 6 microM) inhibited, in a non-competitive way, the increase in tension evoked by Ca2+ with depression of the maximum response. On the other hand, (+)-nantenine (3 - 30 microM) did not affect the contractile effect caused by okadaic acid (OA, 1 microM) while, however, this alkaloid totally relaxed, in a concentration-dependent fashion, the contractions produced by phorbol 12-myristate 13-acetate (PMA, 1 microM) in endothelium-containing rat aortic rings. (+)-Nantenine (1 - 30 microM) reversed and competitively antagonized the inhibitory action induced by B-HT 920 in electrically-stimulated rat vas deferens. In isolated rat atria, (+)-nantenine (3 - 10 microM) diminished the contraction frequency. (+)-Nantenine (3 microM) significantly reduced the depolarization (voltage)-activated transient (T-type) and sustained (long-lasting, L-type) barium inward currents [ IBa(T) and IBa(L) ] recorded in whole cell-clamped rat aortic myocytes. These results indicate that the pharmacological effects of (+)-nantenine observed at concentrations lower than 1 microM can be attributed to alpha 1 -adrenergic and 5-HT 2A receptor blocking properties whereas at higher concentrations (> 1 microM) the pharmacological activity of this natural compound may be also due to a decrease of Ca2+ influx through transmembrane calcium channels (calcium antagonist activity), to an inhibition of PKC actions and/or to an alpha 2 -adrenoceptor blockade.

Alkaloids↗
PubMed2003

Tamoxifen derivatives for delivery of the antitumoral (DACH)Pt group: selective synthesis by McMurry coupling, and biochemical behaviour.

The goal of our study was to potentiate the effects of the ((R,R)-trans-1,2-diaminocyclohexane)-platinum(II) fragment [(DACH)Pt], known for its cytotoxic properties, either with tamoxifen (Tam), the most widely used antiestrogen in the treatment of hormone-dependent breast cancers, or with its active metabolite hydroxytamoxifen (hydroxy-Tam). We coupled Tam or hydroxy-Tam derivatives bearing a malonato group at the para position of the beta aromatic ring with the (DACH)Pt fragment. The malonato-Tam and malonato-hydroxy-Tam compounds were prepared through McMurry coupling of the appropriate ketones. The presence of the malonate group resulted in a pronounced stereospecificity in the reaction, since malonato-Tam was obtained only as the Z isomer, while malonato-hydroxy-Tam was obtained as an 80/20 E/Z mixture. Attribution of the isomeric structures was achieved by 2D NMR spectroscopy. The platinum complexes (DACH)Pt-malonato-Tam and (DACH)Pt-malonato-hydroxy-Tam were then prepared by coupling the barium salts derived from the malonato-Tam and malonato-hydroxy-Tam with the nitrate derived from (DACH)PtCl(2). Study of the biochemical properties of these two platinum complexes showed that, while the hydroxy-Tam complex is satisfactorily recognized by the estrogen receptor (relative binding affinity, RBA=6.4 %), the Tam complex is less well recognized (RBA=0.5 %). The effects of these complexes on two hormone-dependent breast cancer cell lines (MCF7 and MVLN) were studied in vitro. Both complexes showed an antiproliferative effect on MCF7 cells, and an antiestrogenic effect on MVLN cells. The observed effects appear to be essentially antihormonal, since incorporation of the (DACH)Pt fragment into the tamoxifen skeleton did not cause an increase in the cytotoxicity of the complexes.

Antineoplastic Agents, Hormonal↗
PubMed1997

Mammalian retinal glial (Müller) cells express large-conductance Ca(2+)-activated K+ channels that are modulated by Mg2+ and pH and activated by protein kinase A.

The cell-attached and excised patch configurations of the patch clamp technique were used to characterize Ca(2+)-activated maxi-K+ channels in freshly-isolated Müller glial cells. The cells were dissociated from postmortem adult human and porcine retinas. The maxi-K+ channels in Müller cells of both species display a single channel conductance of 175 pS in cell-attached and inside-out patches (125/110 mM K+). The channels are activated by membrane depolarization and by elevation of intracellular Ca2+. In the presence of 10(-5), 10(-4), and 10(-3) M intracellular free Ca2+, the half-activation voltages are +7.2, -26.6, and -47.5 mV, respectively. The half-activation-[Ca2+] at +10 mV is 8.1 microM, and the Hill coefficient of Ca2+ binding is 1.7, Ba2+ exerts a voltage-dependent block of the open-state probability. The maxi-K+ channels of Müller cells are activated by raising of the intracellular pH as well as by Mg2- ions at the cytosolic face of the channels. Phosphorylation of the channel after cytosolic addition of the catalytic subunit of a cAMP dependent protein kinase in the presence of Mg-ATP caused a shift of the activation curve to negative membrane potentials. Between -40 and -80 mV membrane potentials, the open-state probability rose to 190.3% of the control value (100%) after phosphorylation of the channel. Therefore, phosphorylation enhances sensitivity of the channels to Ca2+ and voltage. The maxi-K+ channels may provide a link between second messenger systems and membrane conductance of retinal Müller cells and may have an important function in repolarization of the Müller cell membrane and, therefore, in the maintainance of the retinal spatial K+ buffering mechanisms.

Adenosine Triphosphate↗
PubMed1993

Potassium channel antagonists and vascular reactivity in stroke-prone spontaneously hypertensive rats.

The goal of this study was to characterize differences in contractile responsiveness to several potassium channel antagonists in vascular smooth muscle from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto normotensive rats (WKY). Helically-cut strips of carotid arteries (endothelium removed) from SHRSP and WKY were mounted in muscle baths for measurement of isometric force generation. Contractile responses to tetraethylammonium (10(-4) to 3 x 10(-2) mol/L) and barium (3 x 10(-5) mol/L), blockers of the voltage-dependent and large conductance, calcium activated potassium channels, were greater in carotid arteries from SHRSP than in those from WKY. In contrast, contractile responses to the voltage-dependent potassium channel blockers 3,4-diamino-pyridine (10(-6) to 3 x 10(-3) mol/L) and sparteine (10(-6) to 3 x 10(-2) mol/L) in arteries from SHRSP did not differ from WKY values. Carotid arteries from SHRSP and WKY did not contract to apamin (10(-9) to 10(-6) mol/L), an antagonist of the small conductance, calcium activated potassium channel. Furthermore, relaxation responses to diazoxide (3 x 10(-4) mol/L), an activator of the ATP-sensitive potassium channel, and subsequent contractions to the ATP-sensitive potassium channel blocker glyburide (10(-8) to 3 x 10(-6) mol/L) in arteries from SHRSP did not differ from WKY values. Carotid artery segments from SHRSP were more sensitive to the contractile effects of elevated potassium than those from WKY. We conclude that altered activity of the large conductance, calcium activated potassium channel may play a role in the increased responsiveness observed in arteries from SHRSP.

4-Aminopyridine↗
PubMed1989

Characterization of cellular transport, subcellular distribution, and secretion of the neurotoxicant 1-methyl-4-phenylpyridinium in bovine adrenomedullary cell cultures.

Cultures of bovine adrenomedullary chromaffin cells accumulated 1-[methyl-3H]methyl-4-phenylpyridinium ([3H]MPP+) in a time- and concentration-dependent manner with an apparent Km of 0.7 microM and a Vmax of 3 pmol/min/10(6) cells. The uptake was sodium dependent and sensitive to inhibitors of the cell-surface catecholamine transporter. At low concentrations of MPP+, the subcellular distribution was identical to that of endogenous catecholamines in the catecholamine-containing chromaffin vesicles. However, at a higher concentration of MPP+, a larger proportion of the toxicant was recovered in the cytosolic fraction, with less in the chromaffin vesicle fractions. When cells were prelabeled with [3H]MPP+, at 1 and 300 microM, and then permeabilized with digitonin in the absence of Ca2+, there was a proportionally greater release of MPP+ from the cells labeled at the higher concentration of the toxicant. In the presence of Ca2+, cell permeabilization induced a time-dependent secretion of catecholamines and a parallel secretion of MPP+. Under these conditions, the secretion of endogenous catecholamines was unaffected by the presence of MPP+. When the permeabilization studies were carried out in the presence of tetrabenazine, a massive release of MPP+ was observed in the absence of Ca2+ and was not further increased by Ca2+. In intact cells prelabeled with 300 microM [3H]MPP+, the secretagogues nicotine and veratridine elicited a Ca2+ -dependent secretion of catecholamines and MPP+ from the cells in similar proportions to their cellular contents. Barium-induced release of both species was independent of external Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗
PubMed1996

Characterization of inwardly rectifying potassium currents from dissociated rat taste receptor cells.

Inwardly rectifying potassium currents were recorded from taste receptor cells dissociated from the rat tongue with the use of patch-clamp techniques in the whole cell configuration. These currents displayed strong inward rectification at potentials negative to the potassium reversal potential and little outward current at potentials positive to it. With elevations of external potassium concentration, the slope and chord conductance increased, activation shifted toward more depolarized potentials, and the reversal potential varied in a predicted Nernst relationship. These currents were insensitive to 4-aminopyridine and partially blocked by tetraethylammonium. Both barium and cesium gave more complete blocks with characteristic relief at more negative potentials. Inhibition with barium was more voltage sensitive than with cesium. These currents were unaffected by changes in external sodium. The high conductance at negative membrane potentials suggests these currents may contribute with other conductances to the resting potential of taste cells. They may also participate in yet unidentified processes of taste transduction, resulting in the early depolarization of the resting potential.

4-Aminopyridine↗
PubMed1996

Muscarinic activation of a voltage-dependent cation nonselective current in rat association cortex.

The ionic mechanism underlying the acetylcholine-induced depolarization of layer V pyramidal neurons of rat prefrontal cortex was examined using whole-cell recording in in vitro rat brain slices. Consistent with previous results, pressure application of acetylcholine to layer V pyramidal neurons elicited a strong depolarization. Pharmacological analysis of this response indicated that it was mediated by the stimulation of muscarinic receptors as it was mimicked by muscarinic agonists, but not by nicotine, and was blocked by atropine. The inward current responsible for the depolarization resulted from the activation of a voltage-dependent, cation nonselective current. Thus, the amplitude of the current was critically dependent on extracellular sodium concentration but not on extracellular potassium or chloride concentration. Examination of the I-V relationship for the muscarinic current using voltage clamp revealed that the current reversed near -15 mV and exhibited a strong voltage dependence, turning off rapidly in the subthreshold range. The voltage dependence of the current led to the appearance of a current associated with a conductance decrease when examined using steady-state voltage- or current-clamp measurements. This might have led to earlier misidentification of this response as mediated by a decrease in potassium conductance. These results question the traditional interpretation that muscarinic depolarization in cortex is mediated by a decrease in potassium conductance. They indicate that the fundamental mechanism responsible for muscarinic depolarization in prefrontal cortex involves the activation of a voltage-dependent, cation nonselective current. This current might represent a previously unsuspected mechanism capable of mediating slow depolarization in the central nervous system.

Acetylcholine↗
PubMed1995

Blockade by sigma site ligands of high voltage-activated Ca2+ channels in rat and mouse cultured hippocampal pyramidal neurones.

1. The effects of a series of structurally-dissimilar sigma site ligands were examined on high voltage-activated Ca2+ channel activity in two preparations of cultured hippocampal pyramidal neurones. 2. In mouse hippocampal neurones under whole-cell voltage-clamp, voltage-activated Ca2+ channel currents carried by barium ions (IBa) were reduced with the rank order (IC50 values in microM): 1S,2R-(-)-cis-N-methyl-N-[2-(3,4-dichlorophenyl)ethyl]- 2-(1-pyrrolidinyl)cyclohexylamine (7.8) > rimcazole (13) > haloperidol (16) > ifenprodil (18) > opipramol (32) > carbetapentane (40) = 1-benzylspiro[1,2,3,4-tetrahydronaphthalene-1,4-piperidine] (42) > caramiphen (47) > dextromethorphan (73). At the highest concentrations tested, the compounds almost abolished IBa in the absence of any other pharmacological agent. 3. The current-voltage characteristics of the whole-cell IBa were unaffected by the test compounds. The drug-induced block was rapid in onset and offset, with the exceptions of carbetapentane and caramiphen where full block was achieved only after two to three voltage-activated currents and was associated with an apparent increase in the rate of inactivation of IBa. 4. In rat hippocampal neurones loaded with the Ca(2+)-sensitive dye Fura-2, rises in intracellular free Ca2+ concentration evoked by transient exposure to 50 mM K(+)-containing medium, either in the absence or in the presence of 10 microM nifedipine (to block L-type high voltage-activated Ca2+ channels), were also reversibly attenuated by the sigma ligands. The rank order potencies for the compounds in these experimental paradigms were similar to that observed for blockade of IBa in the electrophysiological studies. 5. These results indicate that, at micromolar concentrations, the compounds tested block multiple subtypes of high voltage-activated Ca2+ channels. These actions, which do not appear to be mediated by high-affinity sigma binding sites, may play a role in some of the functional effects previously described for the compounds.

Animals↗
PubMed1995

[MR imaging of colonic cancer with retrograde administration of contrast material containing ferric ammonium citrate].

MR imaging was performed with the retrograde administration of ferro-magnetic contrast material and air in 10 patients with rectosigmoid colon cancer. The border of the lesions was well demonstrated in spin echo images, and MR imaging yielded additional diagnostic information to that provided by barium enemas and CT scans in all cases. In conclusion, this type of contrast material seemed promising in the MRI diagnosis of rectal lesions.

Administration, Rectal↗
PubMed1983

Sample preparation by salts precipitation and quantitation by high-performance liquid chromatography with UV detection of selected drugs in biological fluids.

A quantitative clean-up procedure for drugs in plasma and urine in preparation for high-performance liquid chromatographic analysis is discussed. Samples are mixed with zinc sulfate, barium hydroxide, and acetonitrile (or methanol). Resultant solutions are clear and free of visible residue. Injections of over 420 samples of treated urine and 120 samples of treated plasma had no noticeable effect on pressure drop and column performance. An examination of the column head indicated no damage or discoloration to the packing. Baselines of the controls show no interference from endogenous compounds for the drugs studied. Precision study using cyclobenzeprine . HCl in plasma and urine by internal standard and external standard methods has within-run and day-to-day variations of under 5%. Drugs studied in urine and plasma are amiloride . HCl, cyclobenzeprine . HCl, cyproheptadine . HCl, diflunisal, indomethacin, phenylbutazone and sulindac. These drugs are selected for the various functional groups, their binding by proteins and their natural UV absorptivity. Conditions to improve recovery, advantages and limitations are discussed.

Chemical Precipitation↗
PubMed1992

Functional expression of a probable Arabidopsis thaliana potassium channel in Saccharomyces cerevisiae.

We report the isolation of a cDNA (KAT1) from Arabidopsis thaliana that encodes a probable K+ channel. KAT1 was cloned by its ability to suppress a K+ transport-defective phenotype in mutant Saccharomyces cerevisiae cells. This suppression is sensitive to known K+ channel blockers, including tetraethylammonium and Ba2+ ions. The KAT1 cDNA contains an open reading frame capable of encoding a 78-kDa protein that shares structural features found in the Shaker superfamily of K+ channels. These include a cluster of six putative membrane-spanning helices (S1-S6) at the amino terminus of the protein, a presumed voltage-sensing region containing Arg/Lys-Xaa-Xaa-Arg/Lys repeats within S4, and the highly conserved pore-forming region (known as H5 or SS1-SS2). Our results suggest that the structural motif for K+ channels has been conserved between plants and animals.

Amino Acid Sequence↗
PubMed1994

Na(+)-activated K+ channels localized in the nodal region of myelinated axons of Xenopus.

1. A potassium channel activated by internal Na+ ions (K+Na channel) was identified in peripheral myelinated axons of Xenopus laevis using the cell-attached and excised configurations of the patch clamp technique. 2. The single-channel conductance for the main open state was 88 pS with [K+]o = 105 mM and pS with [K+]o = 2.5 mM ([K+]i = 105 mM). The channel was selectively permeable to K+ over Na+ ions. A characteristic feature of the K+Na channel was the frequent occurrence of subconductance states. 3. The open probability of the channel was strongly dependent on the concentration of Na+ ions at the inner side of the membrane. The half-maximal activating Na+ concentration and the Hill coefficient were 33 mM and 2.9, respectively. The open probability of the channel showed only weak potential dependence. 4. The K+Na channel was relatively insensitive to external tetraethylammonium (TEA+) in comparison with voltage-dependent axonal K+ channels; the half-maximal inhibitory concentration (IC50) was 21.3 mM (at -90 mV). In contrast, the channel was blocked by low concentrations of external Ba2+ and Cs+ ions, with IC50 values of 0.7 and 1.1 mM, respectively (at -90 mV). The block by Ba2+ and Cs+ was more pronounced at negative than at positive membrane potentials. 5. A comparison of the number of K+Na channels in nodal and paranodal patches from the same axon revealed that the channel density was about 10-fold higher at the node of Ranvier than at the paranode. Moreover, a correlation between the number of K+Na channels and voltage-dependent Na+ channels in the same patches was found, suggesting co-localization of both channel types. 6. As weakly potential-dependent ('leakage') channels, axonal K+Na channels may be involved in setting the resting potential of vertebrate axons. Simulations of Na+ ion diffusion suggest two possible mechanisms of activation of K+Na channels: the local increase of Na+ concentration in a cluster of Na+ channels during a single action potential or the accumulation in the intracellular axonal compartment during a train of action potentials.

Animals↗
PubMed1994

Atrial natriuretic peptide enhances activity of potassium conductance in adrenal glomerulosa cells.

Aldosterone secretion from the adrenal glomerulosa (AG) cells is inhibited by atrial natriuretic peptide (ANP). Inasmuch as alterations in K+ conductance can modulate aldosterone secretion, the effect of ANP on intracellular K+ homeostasis was investigated. Intracellular K+ concentration ([K+]i) of AG cells was assessed by spectrofluorometry using the K(+)-sensitive dye, K(+)-binding benzofuran isophthalate. The resting value of [K+]i in AG cells was determined to be 120 +/- 1.2 mM (n = 37) in a HCO3-free, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium. Exposure of AG cells to ANP led to a dose-dependent, transient decrease in [K+]i, from 21 +/- 3.2% (n = 7) at 100 pM to 31 +/- 2.3% at 1 microM (n = 7). In the continued presence of ANP, a rapid recovery to near basal values of [K+]i was attained within 90 s. Measurements of membrane voltage using the potential sensitive dye 1-3(-sulfonatopropyl)-4-[beta-(-(di-n-butylamino)-6-naphthyl)vinyl ]- pyridinium betaine documented an accompanying change in membrane potential. Pretreatment of AG cells with barium (0.5 mM), tetraethylammonium (0.1 mM), charybdotoxin (100 nM), or ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid (0.5 mM) blunted the ANP-induced decrease in [K+]i. ANP-(7-23), the ANP-C-receptor selective agonist, which does not elevate guanosine 3',5'-cyclic monophosphate (cGMP) did not alter [K+]i in contrast to cGMP (50 microM), which did. We conclude that ANP via the activation of the ANP A receptor alters K+ homeostasis through a Ca(2+)-activatable K(+)-conductive pathway likely to be the maxi-K channel.

Animals↗