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PubMed1992

Molecular basis for the inhibition of 1,4-dihydropyridine calcium channel drugs binding to their receptors by a nonspecific site interaction mechanism.

The "membrane bilayer" pathway (Rhodes, D. G., J. G. Sarmiento, and L. G. Herbette. 1985. Mol. Pharmacol. 27:612-623.) for 1,4-dihydropyridine calcium channel drug (DHP) binding to receptor sites in cardiac sarcolemmal membranes has been extended to include the interaction of amphiphiles within the lipid bilayer. These studies focused on the ability of the Class III antiarrhythmic agents bretylium and clofilium to nonspecifically inhibit DHP-receptor binding in canine cardiac sarcolemma. Clofilium was found to inhibit nimodipine binding with an inhibition constant of approximately 5 microM, whereas bretylium had no effect on nimodipine binding. Small angle x-ray diffraction was then used to examine the differential ability of these two Class III agents to inhibit DHP-receptor binding. The time-averaged locations of bretylium, clofilium, and nimodipine in bovine cardiac phosphatidylcholine (BCPC) bilayers (supplemented with 13 mol% cholesterol) were determined to a resolution of 9 A. The location of bretylium as dominated by its phenyl ring in BCPC bilayers was found to be at the hydrocarbon core/water interface, similar to that of the dihydropyridine ring of nimodipine. The location of clofilium as dominated by its phenyl ring was found to be below the hydrocarbon/core water interface within the hydrocarbon chain region of the bilayer, similar to that of the phenyl ring of nimodipine. The location of the dihydropyridine ring portion of nimodipine has previously been shown by neutron diffraction to be located at the hydrocarbon core/water interface of native sarcoplasmic reticulum, consistent with the small angle x-ray data from model membranes in this paper. Therefore, we speculate that the nonspecific inhibition arises from the interaction of clofilium's phenyl ring with the site on the calcium channel receptor where the phenyl ring portion of nimodipine must interact. The DHP-receptor binding pathway would then involve both nonspecific (membrane) and specific (protein) binding components, both of which are necessary for receptor binding.

Animals↗
PubMed1989

Pharmacological characterization of mare uterus motility with special reference to calcium antagonists and beta-2-adrenergic stimulants.

1. Uterine motility was studied in vitro in the myometrial tissue obtained from pregnant and non-pregnant mares. 2. The spontaneous contractions of the preparations were not modified by tetrodotoxin, by anticholinergics, antiadrenergics, histamine H1 and H2 blockers, antiserotoninergic and opioid antagonists; but disappeared in Ca2+ and Na+ free medium. 3. beta 2-adrenergic stimulants like salbutamol and hexoprenaline and the calcium channel blockers nifedipine and verapamil were effective inhibitors of the amplitude of phasic contractions (ID50S for salbutamol and nifedipine were 7.7 nM and 14.6 nM, respectively in oestrus preparations). 4. The above data indicated that the mare myometrium contractility in vitro is very sensitive to the action of beta 2 mimetic compounds and calcium antagonists; nifedipine, in particular, seems to be a very promising alternative to beta 2 stimulants in the tocolytic therapy.

Adrenergic beta-Agonists↗
PubMed2002

Capacitative Ca(2+) entry in vascular endothelial cells is mediated via pathways sensitive to 2 aminoethoxydiphenyl borate and xestospongin C.

1. Agonists increase endothelial cell intracellular Ca(2+), in part, by capacitative entry, which is triggered by the filling state of intracellular Ca(2+) stores. It has been suggested that depletion of endoplasmic reticulum (ER) Ca(2+) stores either leads to a physical coupling between the ER and a plasma membrane channel, or results in production of an intracellular messenger which affects the gating of membrane channels. As an axis involving the IP(3) receptor has been implicated in a physical coupling mechanism the aim of this study was to examine the effects of the putative IP(3) receptor antagonists/modulators, 2 aminoethoxydiphenyl borate (2APB) and xestospongin C, on endothelial cell Ca(2+) entry. 2. Studies were conducted in fura 2 loaded cultured bovine aortic endothelial cells and endothelial cells isolated from rat heart. 3. 2APB (30 - 300 microM) inhibited Ca(2+) entry induced by both agonists (ATP 1 microM, bradykinin 0.1 microM) and receptor-independent mechanisms (thapsigargin 1 microM, ionomycin 0.5 and 5 microM). 2APB did not diminish endothelial cell ATP-induced production of IP(3) nor effect in vitro binding of [(3)H]-IP(3) to an adrenal cortex binding protein. Capacitative Ca(2+) entry was also blocked by disruption of the actin cytoskeleton with cytochalasin (100 nM) while the initial Ca(2+) release phase was unaffected. 4. Similarly to 2APB, xestospongin C (3 - 10 microM) inhibited ATP-induced Ca(2+) release and capacitative Ca(2+) entry. Further, xestospongin C inhibited capacitative Ca(2+) entry induced by thapsigargin (1 microM) and ionomycin (0.5 microM). 5. The data are consistent with a mechanism of capacitative Ca(2+) entry in vascular endothelial cells which requires (a) IP(3) receptor binding and/or an event distal to the activation of the ER receptor and (b) a spatial relationship, dictated by the cytoskeleton, between Ca(2+) release and entry pathways.

Actins↗
PubMed2006

Opposite diastereoselective activation of P2Y1 and P2Y11 nucleotide receptors by adenosine 5'-O-(alpha-boranotriphosphate) analogues.

BACKGROUND AND PURPOSE: We explored the stereoselective activation of the P2Y11 receptor, stably expressed and tagged with GFP, in 1321N1 cells, in comparison to its closest homologue, the P2Y1 receptor. EXPERIMENTAL APPROACH: The potency of several chiral ATP analogues was determined by measuring increases in intracellular calcium concentration ([Ca2+]i). In a series of ATP-alpha-B and ATP-alpha-S analogues, a non-bridging oxygen atom of Palpha was substituted by BH3 or sulphur, respectively, introducing a chiral center at Palpha. The pairs of diastereoisomers (A and B isomers) were each applied as purified compounds. KEY RESULTS: The (B) isomers (ATP-alpha-B Sp isomers and ATP-alpha-S Rp isomers) of all derivatives tested were more potent at the P2Y11 receptor than the corresponding (A) isomers (ATP-alpha-B Rp isomers and ATP-alpha-S Sp isomers) and the parent compounds. This characteristic of the P2Y11 receptor is opposite to the behaviour of the same diastereoisomers at the P2Y1 receptor, at which the (A) isomers are more active. CONCLUSIONS AND IMPLICATIONS: The distinctly opposite diastereoselective activity of ATP derivatives at the P2Y11 and the P2Y1 receptor will allow the deciphering of structural differences of the ligand recognition sites between these receptor subtypes and may aid in the development of subtype-selective agonists. Moreover, ATP-alpha-B diastereoisomers are not active at the P2Y2 receptor. Thus, they are compounds suitable for distinguishing the functional contribution of the two ATP-activated P2Y receptors, the P2Y2 and P2Y11 receptor, in physiological or pathophysiological responses of cells.

Adenosine Triphosphate↗
PubMed2006

Tilted angle CZT detector for photon counting/energy weighting x-ray and CT imaging.

X-ray imaging with a photon counting/energy weighting detector can provide the highest signal to noise ratio (SNR). Scanning slit/multi-slit x-ray image acquisition can provide a dose-efficient scatter rejection, which increases SNR. Use of a photon counting/energy weighting detector in a scanning slit/multi-slit acquisition geometry could provide highest possible dose efficiency in x-ray and CT imaging. Currently, the most advanced photon counting detector is the cadmium zinc telluride (CZT) detector, which, however, is suboptimal for energy resolved x-ray imaging. A tilted angle CZT detector is proposed in this work for applications in photon counting/energy weighting x-ray and CT imaging. In tilted angle configuration, the x-ray beam hits the surface of the linear array of CZT crystals at a small angle. This allows the use of CZT crystals of a small thickness while maintaining the high photon absorption. Small thickness CZT detectors allow for a significant decrease in the polarization effect in the CZT volume and an increase in count rate. The tilted angle CZT with a small thickness also provides higher spatial and energy resolution, and shorter charge collection time, which potentially enables fast energy resolving x-ray image acquisition. In this work, the major performance parameters of the tilted angle CZT detector, including its count rate, spatial resolution and energy resolution, were evaluated. It was shown that for a CZT detector with a 0.7 mm thickness and 13 degrees tilting angle, the maximum count rate can be increased by 10.7 times, while photon absorption remains >90% at photon energies up to 120 keV. Photon counting/energy weighting x-ray imaging using a tilted angle CZT detector was simulated. SNR improvement due to optimal photon energy weighting was 23% and 14% when adipose contrast element, inserted in soft tissue with 10 cm and 20 cm thickness, respectively, was imaged using 5 energy bins and weighting factors optimized for the adipose. SNR improvement was 42% and 31% when CaCO(3) contrast element, inserted in soft tissue with 10 cm and 20 cm thickness, respectively, was imaged using 5 energy bins and weighting factors optimized for CaCO(3). The SNRs of the photon counting single-kVp dual-energy subtracted images of CaCO(3) and adipose were higher by 2.04 and 2.74 times, respectively, as compared to currently used dual-kVp dual-energy subtracted images. Experiments with a CZT crystal with 2 mm thickness have shown significant decrease in the tailing effect of the CZT pulse spectrum at 59 keV and 122 keV photon energies, when the tilting angle configuration was used. Finally, feasibility of the tilted angle CZT detector for photon counting cone beam breast CT imaging was demonstrated.

Artifacts↗
PubMed1997

Photodynamic triggering of calcium oscillation in the isolated rat pancreatic acini.

1. Photodynamic agents, due to their photon-dependent selective activation, can selectively activate a number of physiological processes and may directly modulate signal transduction in a number of cells including pancreatic acinar cells. 2. Activation of the photodynamic agent sulphonated aluminium phthalocyanine (SALPC) triggered recurrent cytosolic calcium ([Ca2+]i) spiking in pancreatic acinar cells. 3. The photodynamically triggered calcium spiking could be blocked by phosphatidylinositol-specific phospholipase C (PI-PLC) inhibitor U73122, but not by phosphatidylcholine-specific phospholipase C inhibitor D609. 4. Removal of extracellular Ca2+ abolished spiking, as did 2-aminoethoxydiphenylborate (2-APB), an inhibitory modulator of IP3-mediated Ca2+ release from intracellular stores. 5. These data suggest that SALPC photodynamic action may permanently fix PI-PLC in an active conformation, and this produced recurrent [Ca2+]i spiking.

Animals↗
PubMed1990

Intracellular recording from neurones of the guinea-pig gall-bladder.

1. Intracellular recordings were made from neurones of the guinea-pig gall-bladder in vitro. Intracellular injection of horseradish peroxidase revealed a simple structure, consisting of a soma and a single process, but no discernible dendritic arborization. 2. The resting membrane potential was -50.5 +/- 0.4 mV and the input resistance was 80 M omega. 3. Gall-bladder neurones spiked only once at the onset of depolarizing current pulses. Action potentials were blocked by tetrodotoxin, but a Ca2(+)-dependent spike could be elicited in the presence of tetrodotoxin and tetraethylammonium. 4. Action potential after-hyperpolarizations had a duration of 172 +/- 3.7 ms and reversed at a membrane potential of -93 mV; this reversal potential was linearly related to the logarithm of the external potassium concentration. The initial phase of the after-hyperpolarization was inhibited by tetraethylammonium (1-10 mM) and was not affected by 3,4-diaminopyridine. The late phase of the after-hyperpolarization was blocked by apamin (10 nM) or curare (500 microM). Both the early and late phases of the after-hyperpolarization were inhibited when the preparation was perfused with a calcium-free, high-magnesium solution. The calcium-free, high-magnesium solution had no effect on the membrane potential or input resistance of these cells. 5. Fast excitatory synaptic responses and antidromic responses were elicited in gall-bladder neurones by focal stimulation of fibre tracts. High-frequency fibre tract stimulation often resulted in prolonged, calcium-dependent, depolarizations that were associated with a decrease in input resistance. 6. 5-Hydroxytryptamine and substance P caused depolarizations that were associated with a decrease in input resistance. Bethanechol caused hyperpolarizations that were associated with a decrease in input resistance and which were blocked by atropine.

4-Aminopyridine↗
PubMed2006

An extremely stable host-guest complex that functions as a fluorescence probe for calcium ions.

Herein, we report a crown ether based molecular cage that forms extremely stable supramolecular complexes with dimethyldiazapyrenium (DMDAP) ions in CD(3)CN through the collaboration of multiple weak C-HO hydrogen bonds. The very strong binding affinity in this host-guest system allows the molecular cage to bleach the fluorescence signal of DMDAP substantially in equimolar solutions at concentrations as low as 1 x 10(-5) M. Remarkably, a 1x10(-5) M equimolar solution of the molecular cage and DMDAP is highly selective toward Ca(2+) ions-relative to other biologically important Li(+), Na(+), K(+), and Mg(2+) ions-and causes a substantial increase in the fluorescence intensity of the solution. As a result, this molecular cage/DMDAP complex behaves as a supramolecular fluorescence probe for the detection of Ca(2+) ions in solution.

Aza Compounds↗
PubMedDate not supplied

Sevoflurane degradation product concentrations with soda lime during prolonged anesthesia.

STUDY OBJECTIVES: To evaluate the decomposition of sevoflurane in soda lime during prolonged sevoflurane anesthesia in humans. To evaluate for evidence of renal or hepatotoxicity as a result of exposure to these sevoflurane degradation compounds. DESIGN: Prospective evaluation in healthy volunteers. SETTING: Clinical research unit and postanesthesia care unit of a university hospital. PATIENTS: Six healthy male volunteers. INTERVENTIONS: Subjects were anesthetized with sevoflurane 1 to 1.2 minimum alveolar concentration for greater than 9 hours with a semiclosed circuit anesthetic technique (5-liter total flow) with fresh soda lime as the absorbent. MEASUREMENTS AND MAIN RESULTS: Laboratory tests of renal and hepatic function were performed before anesthesia and 1 and 5 days after anesthesia. During sevoflurane anesthesia, inhalation and exhalation circuit limb gas samples were obtained for degradation compound analysis. Only one degradation product, fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether (compound A), was detected. Inhalation concentration was maximal (7.6 +/- 1.0 ppm) at 2 hours and did not increase further after this time point. There were no differences in preanesthesia and postanesthesia tests of hepatic and renal function. CONCLUSIONS: Levels of the degradation compound (compound A) produced in semiclosed circuit sevoflurane anesthesia with soda lime are well below potential toxic levels and thus appear safe. When sevoflurane is administered under these conditions for prolonged anesthesia, concentrations of compound A do not continue to increase throughout anesthesia.

Adsorption↗
PubMed1999

Effects of veratrine and paeoniflorin on the isolated rat aorta.

The interactions and mechanisms between veratrine and paeoniflorin on the isolated rat aorta were studied. Veratrine (1x10(-6) to 1x10(-4) g/ml) could induce contraction on the isolated rat aorta in a concentration-related manner. Paeoniflorin had no effect on the isolated rat aorta. Pretreatment with prazosin (1x10(-6) M) and nifedipine (1x10(-6) M) but not yohimbine (1x10(-5) M) could decrease the tension of contraction induced by veratrine (1x10(-4) g/ml). Sodium nitroprusside (1x10(-4) M) could inhibit the contraction induced by veratrine (1x10(-4) g/ml) with or without endothelium, whereas methylene blue (5x10(-5) M) could increase the contraction induced by veratrine (1x10(-4) g/ml). Treatment with veratrine (1x10(-4) g/ml) could decrease the tension of contraction induced by norepinephrine (1x10(-6) M) or phenylephrine (1x10(-4) M). The inhibition of veratrine on norepinephrine-induced contraction was potentiated by L-arginine (1x10(-4) M) and reversed by L-NAME (1x10(-5) M). Paeoniflorin (1x10(-4) M) could decrease the tension of contraction induced by veratrine (1x10(-4) g/ml) and methylene blue (5x10(-5) M). The inhibition of paeoniflorin on veratrine was more potent on rat isolated aorta with endothelium than without endothelium. Ryanodine (1x10(-5) M) and Ca2+ -free medium could inhibit methylene blue-induced contraction. From the above results, the relaxation of veratrine on the norepinephrine-induced contraction might be related to the increase of NO and cGMP. The contraction of veratrine on the isolated rat aorta was via the increase of intracellular calcium which was inhibited by paeoniflorin.

Animals↗
PubMed2004

Multiple pathways regulate the induction of genes during zoosporogenesis in Phytophthora infestans.

Zoospores are a critical component of the disease cycles of most oomycete pathogens. To better understand this stage, genes induced during zoosporogenesis were identified from Phytophthora infestans, the potato late blight pathogen. Using cDNA arrays representing 2,600 genes expressed during zoosporogenesis, 69 genes showing >fourfold increases in mRNA levels were identified, of which 22 exhibited >100-fold induction. Included were putative protein kinases, transcription factors, ion channels, and other regulators. The expression of 15 genes was characterized in detail using zoosporogenesis time courses, other developmental stages, different temperature regimes, and tissue treated with signaling inhibitors. The latter were of interest because zoosporogenesis is known to be cold induced and inhibited by calcium channel blockers such as verapamil; moreover, in this study, inhibitors of phospholipase C (U-73122) and inositol trisphosphate receptor-gated calcium channels (2-aminoethoxydiphenyl borate) also were shown to block zoosporogenesis. The results indicated that the cytoplasmic and transcriptional changes occurring during zoosporogenesis are regulated by several pathways. For example, verapamil inhibited zoosporogenesis but not the up-regulation of most genes; the induction of some genes required while others were independent of calcium or phospholipid signaling; and, although most genes were induced in sporangia at 10 degrees C but not 24 degrees C, one was induced at both temperatures.

Boron Compounds↗
PubMed1984

Motor disorders of the esophagus: diagnosis and treatment.

Esophageal motor disorders may be clearly primary, as in achalasia or diffuse esophageal spasm (DES), or clearly secondary, as in scleroderma or intrathoracic malignancy. In patients with gastroesophageal reflux, abnormal motility of the esophageal body and stomach, and lower esophageal spasm (LES) appear to predispose patients to reflux. It is possible that esophagitis caused by refluxed gastric material then further impairs motility, propagating the injury. Therapeutically, appropriate use of recently available medications, such as calcium channel blockers and metoclopramide, and new applications of previously available agents, such as hydralazine and bethanechol, have improved our ability to relieve symptoms and at times restore more normal motility.

Bethanechol Compounds↗
PubMed2002

Bretylium or 6-OHDA-resistant, action potential-evoked Ca2+ transients in varicosities of the mouse vas deferens.

Action potential-evoked calcium transients in varicosities in mouse vas deferens were monitored using laser scanning confocal microscopy. Their significance was examined by comparison with excitatory junction potentials (EJPs) and neurogenic contractions, both indirect measurements of transmitter release. Bretylium abolished EJPs, as well as the ATP and NA-mediated phases of contraction. However, bretylium revealed a prominent late component of contraction that was atropine-sensitive. Bretylium abolished calcium transients in 21%, enhanced in 16% and had no effect in 63% of varicosities examined. Pre-treatment with 6-OHDA reduced NA levels to below detectable levels but many strings of varicosities still responded to nerve impulses with 'normal' calcium transients. Varicosities in which calcium transients were abolished by these agents were sympathetic. The identity of those varicosities in which calcium transients were resistant to bretylium (sympathetic but no uptake-1 sites, parasympathetic, sensory) remains to be established.

Action Potentials↗
PubMed1997

Short-term inhibition of parathyroid hormone secretion by a calcium-receptor agonist in patients with primary hyperparathyroidism.

BACKGROUND: Surgery is the usual therapy for patients with primary hyperparathyroidism. We investigated the ability of a calcimimetic drug that inhibits parathyroid hormone secretion in vitro to decrease serum parathyroid hormone and calcium concentrations in patients with this disorder. METHODS: We performed a randomized, placebo-controlled study of single oral doses of 4 to 160 mg of the calcium-receptor agonist drug R-568 in 20 postmenopausal women with mild primary hyperparathyroidism. At base line, the mean (+/-SE) serum calcium concentration was 10.7+/-0.2 mg per deciliter (2.67+/-0.05 mmol per liter). Serum parathyroid hormone and calcium were measured repeatedly after each dose, and safety was assessed. RESULTS: Administration of R-568 resulted in a dose-dependent inhibition of parathyroid hormone secretion. The mean serum parathyroid hormone concentration, which was 77+/-11 pg per milliliter (18.8+/-2.7 pmol per liter; normal range, 16 to 65 pg per milliliter [3.9 to 15.9 pmol per liter) at base line, fell by 26+/-8 percent after 20 mg of R-568 (P=0.03), by 42+/-7 percent after 80 mg (P = 0.01), and by 51+/-5 percent after 160 mg (P=0.005). Serum ionized calcium concentrations fell only after the 160-mg dose, with the decrease closely following the decrease in the serum parathyroid hormone concentration. CONCLUSIONS: The calcimimetic drug R-568 reduces serum parathyroid hormone and ionized calcium concentrations in postmenopausal women with primary hyperparathyroidism.

Aged↗
PubMed1976

Membrane perturbation: studies employing a calcium-sensitive dye, arsenazo III, in liposomes.

A metallochromic dye, arsenazo III [2,7-bis-(2-arsonophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid], has been incorporated into the aquenous interspaces of multilamellar liposomes. multilamellar liposomes. Addition of Ca produced no shift in the absorbance spectrum of dye captured by liposomes, whereas disruption of liposomes by Triton X-100, followed by Ca, produced the spectrum chracteristic of the dye-Ca complex: evidence of latency. Addition of excess ethyleneglycol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) reversed the spectal shift. Differences between spectra obtained in this sequence yielded dye efflus. To measure Ca efflux, difference spectra (+/-EGTA) were obtained from cationic liposomes containing Ca after detergent lysis (sensitivity less than 10 mmol/ml). Since liposomes were impermeable either to dye or Ca until perturbed, it was possible to test a variety of membrane-active steroids (diethylstilbesterol, deoxycorticosterone, etiocholanolone) for their capacity to provoke dye efflux from liposomes; preincorporation of cortisol stablized liposomes against dye leak. Immunoglobulin-coated liposomes containing dye were taken up by phagocytes of Mustelus canis, and phagocytic vacuoles stained red-purple after ingestions. Liposomes containing the calcium-sensitive dye constitute a simple, accurate means for determining membrane perturbation and Ca fluxes; their uptake by cells or organelles remains to be exploited further.

Animals↗
PubMed1999

Lipophilic 4-isoxazolyl-1,4-dihydropyridines: synthesis and structure-activity relationships.

A series of 4-isoxazolyl-1,4-dihydropyridines bearing lipophilic side chains at the C-5 position of the isoxazole ring have been prepared. The calcium channel antagonistic activity of these compounds has been evaluated. A hypothetical model for binding of these compounds in the calcium channel is proposed, and the validity of this model is evaluated based on the SAR of this series of calcium binding, especially for the two most active derivatives, 1a, g. The solid-state structure for the most active compound, 1a, has also been determined, and its important features are reported.

Animals↗