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D J Triggle

Publications and source records attributed to D J Triggle.

At least 19 recordsLinked to original sources
PubMed1996

Structure-function relationships of calcium antagonists. Effect on oxidative modification of low density lipoprotein.

Human low density lipoprotein (LDL) incubated with active Ca2+ antagonists from three different chemical groups, 1,4-dihydropyridines that are of reduced activity as Ca2+ antagonists, vitamin E, and probucol, was more resistant than control to copper- or human monocyte-induced oxidation, as assessed by thiobarbituric acid reactive substance (TBARS) content, degradation by J774 macrophages, and relative electrophoretic mobility on agarose gel. In the copper-induced oxidation system, the drugs tested reduced the TBARS levels of LDL in a concentration-dependent manner. The order of potency was vitamin E > felodipine > 2-chloro analog of nifedipine > nifedipine > amlodipine, nitrendipine, verapamil > diltiazem. In agreement with the results of the TBARS assay, felodipine (25 microM) was also the most effective calcium antagonist in the degradation assay, inducing a significant (P<0.05) 97 +/- 2% reduction in the amount of oxidized [125I]LDL degraded by J774 macrophages compared with nifedipine and its 4-nitro analog, amlodipine, and verapamil. The relative mobility of oxidized LDL on agarose gel was reduced significantly (P<0.05) by felodipine (50 microM) and amlodipine (25 and 50 microM) when compared with control, and was similar to that of native LDL, suggesting an effect of these drugs on the net negative charge of oxidized LDL. In the cell-induced oxidation system, both nifedipine and felodipine (25 microM) induced significant (P<0.05) reductions in the TBARS content of LDL (96 +/- 2 and 65 +/- 9%, respectively) compared with amlodipine, verapamil and the 4-nitro analog of nifedipine. However, in this oxidation system nifedipine was a more effective antioxidant than felodipine. Analysis of the structure-function relationships for the effect of 1,4-dihydropyridines on the oxidative modification of LDL suggests an important role for the 2-substitution of the phenyl ring, and an essential role for the dihydropyridine ring. This study clearly shows that Ca2+ antagonists from different chemical groups have a concentration-dependent effect as antioxidants against LDL oxidation. However, the order of potency of the drug depends on the oxidation system and the assay used to measure the antioxidant effect. Our data suggest that such a protective effect of Ca2+ antagonists against LDL oxidation could play a role in the antiatherosclerotic effect of these drugs.

Animals↗
PubMed1995

Short-term regulation of neuronal calcium channels by depolarization.

The 1,4-dihydropyridine-sensitive voltage-gated Ca2+ channel is widely distributed in excitable cells. The channel and its several associated drug binding sites are known to be up- and downregulated by a variety of homologous and heterologous influences including membrane depolarization. The neurosecretory GH4C1 cell line possesses L-type channels. Depolarization of these cells by elevated K+ increases the binding affinity of 1,4-dihydropyridines and decreases the number of 1,4-dihydropyridine binding sites and functional channels. There is a coordinate upregulation of the number of muscarinic receptors. This membrane potential- and Ca(2+)-calmodulin-dependent process of channel downregulation may involve internalization of the channel heteromeric complex or, more plausibly, a dissociation of the complex and a concomitant loss of both binding and permeation functions.

Animals↗
PubMed1995

The binding interactions of Ro 40-5967 at the L-type Ca2+ channel in cardiac tissue.

Ro 40-5967 [(1S,2S)-2-[2[3-(2-benzamidopropyl]- methylamino]ethyl]-6-fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphthyl- methoxyacetate] is a new Ca2+ channel antagonist active at L-type channels. Radioligand binding studies in cardiac tissue show that Ro 40-5967 does not inhibit 1,4-dihydropyridine binding, but does inhibit diltiazem, desmethoxyverapamil and SR 33557 binding with IC50 values of 8 x 10(-9), 10(-8) and 5 x 10(-8) M, respectively. Equilibrium and kinetic binding studies showed that Ro 40-5967 inhibited both desmethoxyverapamil and SR 33557 binding in an apparently competitive manner. Ro 40-5967 defines an additional and possibly unique antagonist binding site on the L-type voltage-gated Ca2+ channel.

Animals↗
PubMed1995

Age-dependent changes in voltage-gated calcium channels and ATP-dependent potassium channels in Fischer 344 rats.

1. Radioligand binding and 45Ca2+ uptake measurements quantitated ion channel numbers and properties in brain membranes from Fischer 344 rats at 6, 12, 18 and 30 months of age. 2. Decreases in 1,4-dihydropyridine density occurred in striatum, hippocampus and cortex with a decreased affinity. 3. Decreases in w-conotoxin binding occurred in hippocampus and striatum with an increase in affinity. 4. K+ depolarization-mediated 45Ca2+ uptake decreased only in striatum at 18 months. 5. Decreases in glibenclamide binding occurred in cortex and cerebellum at 12-30 months. 6. No changes in 1,4-dihydropyridine binding occurred with age in heart, but glibenclamide binding density was significantly decreased at 30 months.

Adenosine Triphosphate↗
PubMed1995

Decreased dihydropyridine receptor number in hypertensive rat vascular muscle cells.

To further investigate the altered function of Ca2+ channels in vascular muscle cells in hypertension, a novel fluorescently labeled dihydropyridine was used with ultrahigh-sensitivity photometry to study dihydropyridine binding sites on the surface membrane of living vascular muscle cells from stroke-prone spontaneously hypertensive rats and their normotensive controls. Fluorescent nitrobenzoxadiazol-6-dihydropyridine in concentrations of 1 to 100 nmol/L bound specifically to vascular muscle cells' Ca2+ channels, and was displaced by the unlabeled dihydropyridine analogue or nisoldipine (10 mumol/L). Stroke-prone spontaneously hypertensive rat vascular muscle cells showed significantly decreased binding of nitrobenzoxadiazol-6-dihydropyridine compared with normotensive National Institutes of Health rats. Decreased binding of dihydropyridine by vascular muscle cells from stroke-prone spontaneously hypertensive rats (cells that in other studies show increased Ca2+ channel function) indicates a change in channel regulation that is possibly due to a deficiency in the inactivation mechanism, consistent with our earlier electrophysiological studies reporting deficiencies in Ca(2+)-dependent inactivation in genetic hypertension. These data demonstrate decreased numbers of localized sites of dihydropyridine binding on the sarcolemma of living vascular muscle cells, and support the hypothesis that Ca2+ channel alterations may significantly contribute to the molecular etiology of genetic hypertension.

4-Chloro-7-nitrobenzofurazan↗
PubMed1995

Calcium channel antagonists: cardiovascular selectivity of action.

The activities of a series of calcium antagonists including nifedipine, verapamil, diltiazem and second-generation 1,4-dihydropyridines were determined in isolated vascular and cardiac preparations by tissue pharmacology and radioligand binding methods. The inhibitory effects against responses induced by 80 mM K+ depolarization in rat tail artery and against contractions evoked in electrically paced rat papillary muscle were determined. Comparison of these IC50 values defines a vascular/cardiac ratio as an index of relative activities in these tissues. Competition studies of the 1,4-dihydropyridines with [3H]PN 200,110 binding in neonatal rat myocytes under polarized (5.8 mM K+) and depolarized (50 mM K+) states yields an index of voltage-dependent binding. The 1,4-dihydropyridine calcium antagonists exhibit significantly higher vascular/cardiac ratios (31-877) than do the nondihydropyridines (1.9-2.1); with the exception of amlodipine, the second-generation 1,4-dihydropyridines have a higher vascular selectivity than the first-generation nifedipine. The ratios of voltage-dependent binding and vascular selectivity correlate well, consistent with a relationship between the two processes. A similar relationship is also observed in a small series of amlodipine derivatives bearing heterocyclic substituents at the 2-position of the 1,4-dihydropyridine ring. These results suggest that calcium antagonists, especially the 1,4-dihydropyridines do show different degrees of vascular selectivity and that voltage-dependent binding, influenced by chemical structure, is a major, but probably not exclusive, determinant of this selectivity.

Animals↗
PubMed1994

On the other hand: the stereoselectivity of drug action at ion channels.

Ion channels are pharmacological receptors with specific drug binding sites. These binding sites define specific structure-function relationships for the actions of drug classes. Interpretation of these structure-function relationships may be complex because of state-dependent drug-channel interactions. These state-dependent interactions determine affinity and access of drug to binding sites and may result in both quantitative and qualitative changes in structure-function relationships including stereoselectivity. A channel-active drug may exhibit antagonist or activator properties according to membrane potential and the stereoselectivity of interaction may also change with channel state.

Animals↗
PubMed1994

L-type calcium channels: asymmetrical intramembrane binding domain revealed by variable length, permanently charged 1,4-dihydropyridines.

We have used an homologous series of dihydropyridine (DHP) derivatives to determine the location of the binding domain for DHPs on cardiac L-type calcium channels, relative to the extracellular and intracellular membrane surfaces. The series of test molecules consisted of DHP analogs in which the DHP moiety was linked to either a neutral (-CH2CH3) or permanently charged [(-)+N(CH3)3] headgroup and the distance between the headgroup and the active moiety was systematically varied with alkyl spacer chains containing 2, 6, 8, 10, 12, or 16 methylene (-CH2) groups. These compounds were previously shown, by radioligand binding experiments, to interact with the high affinity DHP binding site in intact neonatal rat heart cells. In the present experiments, access to the DHP binding site was assayed by inhibition of L-type calcium channel currents using whole-cell patch-clamp procedures in guinea pig ventricular myocytes. Intracellular application was achieved by dialysis via charged DHP-containing whole-cell patch pipettes, and cell dialysis was monitored by using a charged DHP labeled with a rhodamine fluorophore. Our results show that access of extracellularly applied charged, but not neutral, DHPs to the DHP binding domain depends markedly on the alkyl spacer chain, with the optimal length being near 10 methylene groups. Intracellular application failed to inhibit channel activity for spacer chain lengths up to 16 methylene groups. From our results, we conclude that the DHP binding domain of cardiac L-type calcium channels is not on the extracellular membrane surface but is probably within the lipid bilayer, approximately 11-14 A from the extracellular surface.

Animals↗
PubMed1994

Modulation of L-type Ca2+ channels in clonal rat pituitary cells by membrane depolarization.

The modulation of L-type Ca2+ channels by membrane depolarization, in terms of channel number, function, and interaction with 1,4-dihydropyridine ligands, has been characterized in clonal rat pituitary cells (GH4C1) and rat cerebellar granule cells. Membrane depolarization by 50 mM extracellular K+ for 120 min caused an approximately 90% reduction in the total number of [3H]PN200-110 binding sites (Bmax) and an approximately 20-fold increase in binding affinity in a whole-cell binding assay. Similar results were obtained in a primary culture of rat cerebellar granule cells. In GH4C1 cells the dissociation constant (Kd) and Bmax were changed from 2.15 nM and 214 fmol/mg at 5 mM K+ to 110 pM and 24 fmol/mg at 50 mM K+, respectively. The changes in affinity and Bmax were both dependent on the extracellular K+ concentration. The affinity change resulted from an increased association rate constant (increased from 0.17 to 3.11 x 10(8) M-1 min-1 after depolarization) and an unchanged dissociation rate constant (0.032 min-1). Depolarization for 2 hr reduced the number of [3H]PN200-110 binding sites in the membrane fraction by approximately 50%, but no significant change was detected in total cell homogenates, suggesting removal of L-type Ca2+ channels from the cell surface after depolarization. Blockade of the internalization process by concanavalin A and phenylarsine oxide inhibited the depolarization-induced reduction of L-type Ca2+ channels on the cell surface. A decrease in the number of functional channels on the cell surface, as revealed by stimulated 45Ca2+ uptake, accompanied the change in [3H]PN200-110 binding. Reduction of 45Ca2+ uptake had two exponential components, i.e., rapid (with a time constant of about 2.5 min), with a rapid rate of recovery, and slow (with a time constant of 54 min), with a correspondingly slow rate of recovery. Depolarization of the cells with veratridine (50 microM) or treatment of the cells with the Ca2+ ionophore A23187 (10 microM) had effects similar to those of K+ depolarization on [3H]PN200-110 binding sites and stimulated 45Ca2+ uptake. The change in [3H]PN200-110 binding sites in whole-cell and membrane preparations occurred rapidly, becoming prominent within 45 min, and largely recovered when the cells were repolarized. The down-regulation of L-type Ca2+ channels is dependent on Ca2+ entry via a calmodulin-dependent process.

Animals↗
PubMed1993

New synthetic ligands for L-type voltage-gated calcium channels.

The pharmacology of the L-type Ca2+ channel has been the subject of considerable basic and clinical investigation over the past two decades primarily because of the clinical activities of nifedipine, verapamil and diltiazem. However, it is quite clear that this Ca2+ channel is, in common with other pharmacologic receptors, a multiple drug receptor. There are probably as many as six or more discrete drug binding sites associated with this Ca2+ channel. Continued investigation of these sites may yield both new therapeutic agents, structural clues to ligands active at other classes of Ca2+ channel and structures active at other classes of ion channel.

Animals↗
PubMed1993

Continuous versus intermittent nitroglycerin administration in experimental heart failure: vascular relaxation and radioligand binding to adrenoceptors and ion channels.

Continuous nitroglycerin (NTG) administration causes pharmacologic tolerance in humans and animals, whereas intermittent dosing is capable of avoiding or reducing tolerance development. The mechanism of NTG-induced hemodynamic tolerance may involve specific vascular desensitization and/or neurohormonal compensation. We compared effects of long-term (10 days) NTG administration (continuous or intermittent 12 h on/12 h off transdermal dosing, 10 micrograms/min) to rats with congestive heart failure (CHF) on radioligand binding from selected tissues. Tension responses in isolated blood vessels, plasma renin activity (PRA), plasma Na+ and K+ concentrations were also determined. The maximal binding values (Bmax) for [3H]glyburide and [3H]PN 200 110 in homogenates of left ventricle, right ventricle, and brain were not significantly different after NTG administration (continuous or intermittent), as compared with control. Intermittent, but not continuous, NTG caused significant increases in beta-adrenoceptor densities in the left ventricle, as judged by [3H]dihydroalprenolol binding (Bmax values: intermittent NTG 34.5 +/- 4.8, continuous NTG 24.4 +/- 2.6, placebo control 20.9 +/- 2.9 fmol/mg protein); Kd values for all ligands were not significantly altered by NTG administration. Both intermittent and continuous NTG increased the vascular contractile response to phenylephrine in isolated rat thoracic aorta. Slight reductions (two- to four-fold shifts in EC50 values) in thoracic aorta relaxant response to NTG were observed in both treatment groups as compared with control. Intermittent and continuous NTG administration caused selective changes in beta-adrenoceptor density and vascular response. These changes may contribute partly to the phenomenon of pharmacologic tolerance after chronic nitrate administration.

Administration, Cutaneous↗
PubMed1992

Effect of an homologous series of aliphatic alcohols on neuronal and smooth muscle voltage-dependent Ca2+ channels.

The acute inhibitory actions of alcohol on K(+)-stimulated 45Ca2+ uptake into synaptosomes shows regional variation in sensitivity throughout the brain, suggesting the possibility of a selective action on a specific Ca2+ channel subtype. This was examined by comparing the effects of a homologous series of aliphatic alcohols on synaptosomal Ca2+ channels with their actions on K(+)-stimulated Ca2+ channels in guinea-pig intestinal longitudinal muscle, which have been demonstrated to be of the L-type. K(+)-stimulated contraction of and [3H]nitrendipine binding to smooth muscle were both inhibited by the alcohols at similar concentrations, with the potency increasing with chain length. In synaptosomes, however, K(+)-stimulated 45Ca2+ uptake was 5-30 times more sensitive to the inhibitory actions of alcohol than were [3H]nitrendipine and [125I]omega-conotoxin binding. These observations suggest that K(+)-stimulated 45Ca2+ uptake is mediated by a non-L non-N type channel which is more sensitive to the acute effects of alcohols. This is supported by the observation that K(+)-stimulated 45Ca2+ uptake which is insensitive to L- and N-channel antagonists was inhibited by funnel web spider venom.

Alcohols↗
PubMed1992

Regulation of ATP-sensitive K+ channels by chronic glyburide and pinacidil administration.

Treatment of rats with the K(ATP)+ channel antagonist sulfonylurea, glyburide (3 mg/kg/day, i.p., every 12 hr for 9 days), increased the Bmax value of [3H]glyburide binding to heart and whole brain total membranes by 30 and 24%, respectively. The ligand affinity was unaltered. Treatment with the K+ channel activator, pinacidil (20 mg/kg/day, i.p., every 12 hr for 9 days), did not alter the Bmax value for cardiac [3H]glyburide binding sites, but decreased the Bmax value in the brain by 21%. Chronic administration of hydralazine, which caused an acute reduction in systolic blood pressure equivalent to that of pinacidil, did not alter [3H]glyburide binding in either heart or brain. Treatment with glyburide, pinacidil or hydralazine did not alter L-type calcium channels, assessed by [3H]PN 200 110 binding, in cardiac and brain membranes or small size Ca(2+)-activated K+ channels in brain assessed by [125I]apamin binding. These studies show that the ATP-sensitive class of K+ channels can be regulated following chronic drug treatment in similar fashion to other receptor and channel systems.

Adenosine Triphosphate↗
PubMed1992

Synthesis and muscarinic receptor activity of ester derivatives of 2-substituted 2-azabicyclo[2.2.1]heptan-5-ol and -6-ol.

Radioligand binding affinities of four new muscarinic antagonists and six potential muscarinic agonists which possess the 2-alkyl-2-azabicyclo[2.2.1]heptane ring system have been determined in rat heart, rat brain, and m1- or m3-transfected CHO cell membrane preparations to examine the selectivity for subtypes of muscarinic receptor. The efficacies of the potential muscarinic agonists were determined by the ratio of binding affinities against [3H]QNB and [3H]Oxo-M. Four muscarinic antagonists which have the 2,2-diphenylpropionate side chain at either the C5 (5-endo or 5-exo) or the C6 (6-endo or 6-exo) positions did not discriminate between the subtypes of muscarinic receptors. The 2,2-diphenylpropionate 5-endo substituted compound was the most potent, showing affinities between 4.23 x 10(-10) and 1.18 x 10(-9) M in rat heart, rat brain, and m1- or m3-transfected CHO cell membrane preparations. The rank order of ester potency was 5-endo greater than 5-exo greater than 6-endo greater than 6-exo. A molecular modeling study based on the pharmacophore developed for azaprophen was used to account for the relative potency of these antagonists. Six potential muscarinic agonists which have acetoxy groups in the C5 or C6 position with an N-methyl or N-benzyl substituent did not discriminate subtypes of muscarinic receptors and had affinities between 6.63 x 10(-6) and 4.76 x 10(-5) M in rat heart, rat brain, and m1- or m3-transfected CHO cell membrane preparations. exo-2-Methyl-5-acetoxy-2-azabicyclo[2.2.1]heptane was the most efficacious partial agonist.

Animals↗