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D J Triggle

Publications and source records attributed to D J Triggle.

At least 145 records · Page 8Linked to original sources
PubMed1984

Distinction between high-affinity [3H]phencyclidine binding sites and muscarinic receptors in guinea-pig ileum muscle.

[3H]Phencyclidine ([3H]PCP) binding was studied in guinea-pig ileum muscle membranes. Specific binding of [3H]PCP was time dependent, reversible and saturable, with an equilibrium dissociation constant of 154 nM and maximum binding of 12.9 pmol/mg of protein at pH 9. Its pH dependency suggests that the unionized PCP is the pharmacologically active form. The binding site was on a protein which was sensitive to heat, proteolytic enzymes and the carboxylic group reagent dicyclohexylcarbodiimide, but insensitive to phospholipase A and C, concanavalin A, dithiothreitol and N-ethylmaleimide. Specific [3H]PCP binding was displaced effectively by several PCP analogs and Ca++ channel antagonists including verapamil, to which these sites had a high affinity. These high-affinity PCP-binding sites were found at a much higher concentration in the same membrane preparation than muscarinic receptor sites identified by their specific binding of [3H]quinuclidinyl benzilate. PCP bound to both sites, but with a lower affinity to the muscarinic receptor sites. The PCP and muscarinic receptor sites differed in their sensitivities to pH and drug specifities .

Animals↗
PubMed1984

Interactions of phencyclidine with crayfish muscle membranes. Sensitivity to calcium channel antagonists and other drugs.

[3H]Phencyclidine ( [3H]PCP) bound to crayfish abdominal muscle membranes at pH 7.4 with two affinities (Kd of 0.96 nM for 0.38 pmole/mg of protein, and 18.9 nM for 7.6 pmoles/mg of protein). Binding affinities increased at higher pH, suggesting that binding may be due mostly to the un-ionized form of [3H]PCP. This high-affinity [3H]PCP binding was sensitive to the actions of trypsin, protease, and dicyclohexylcarbodiimide, but insensitive to phospholipase A, concanavalin A,N-ethylmaleimide, and dithiothreitol. Calcium channel antagonists were most potent in inhibiting the high-affinity [3H]PCP binding with the following descending order of potencies: bepridil greater than nicardipine = diltiazem = verapamil greater than cinnarizine greater than (+)-D-600 greater than (-)-D-600 greater than 4-NO2-nifedipine greater than 2-NO2-nifedipine. The binding was also highly sensitive to several PCP analogues, antipsychotics, piperocaine , and tilorone, and moderately sensitive to d-tubocurarine, atropine, imipramine, nortryptyline , and tetracaine. Although verapamil and nifedipine inhibited the action potential of crayfish muscle, PCP did not and actually prolonged slightly the falling phase of the action potential. Although it is unlikely that the [3H]PCP binding protein in crayfish muscles is a Ca2+ channel, it is possible that it may be a K+ channel.

Action Potentials↗
PubMed1984

Effects of metal cations and calmodulin antagonists on [3H] nitrendipine binding in smooth and cardiac muscle.

It was previously reported that [3H]nitrendipine binding to a microsomal fraction from intestinal smooth muscle was dependent upon the presence of divalent metal cations (Bolger et al., J. Pharmacol. Exp. Ther. 225: 291-309, 1983). The effects of cations and calmodulin antagonists on [3H]nitrendipine binding in smooth and cardiac muscle have been studied further. Treatment of ileal and aortic smooth muscle and cardiac muscle with EDTA reduced specific [3H]nitrendipine binding by 70 to 95%. Microsomes from rabbit ventricle were more resistant to EDTA treatment than were those from ileal smooth muscle, but low concentrations of Ca++ (less than 10(-5) M) produced half-maximal restoration of binding in both tissues. The ability of cations at a concentration of 10(-3) M to restore binding to membranes from guinea-pig ileum was in the sequence, Ca++ = Sr++ greater than Mg++ = Mn++ = Co++ greater than Ba++ = Ni++ greater than Zn++ = Cd++ greater than La = Sm = Tm . In contrast to the activation of calmodulin-dependent processes, the ability of these cations to restore [3H]nitrendipine binding did not correlate linearly with ionic radius. However, calmodulin antagonists were found to inhibit [3H]nitrendipine binding with the order of potency: pimozide greater than less than calmidazolium (R 24571) greater than trifluoperazine greater than chlorpromazine greater than promethazine greater than chlorpromazine sulfoxide, that correlates quite well with the potency of these drugs as inhibitors of calmodulin-dependent processes. The results suggest that calmodulin antagonists bind to a protein associated with the [3H]nitrendipine binding site that has a hydrophobic domain similar to that exposed on calmodulin by Ca++, but that this protein is not calmodulin itself.

Animals↗
PubMed1983

Molecular properties of the slow inward calcium channel. Molecular weight determinations by radiation inactivation and covalent affinity labeling.

The slow inward calcium channel, identified by physiologic and pharmacologic responses and [3H]nitrendipine-specific binding, has been characterized by radiation inactivation and covalent affinity labeling. Target size analysis of guinea pig ileum longitudinal smooth muscle membranes indicates a molecular weight of 278,000 for the calcium channel. An affinity label analog of nifedipine and nitrendipine, 2,6-dimethyl-3,5-dicarbomethoxy-4-(2-isothiocyanatophenyl)-1,4-dihydropyridine, was found to inhibit the calcium channel by a covalent interaction with a protein subunit (Mr = 45,000) of the calcium channel.

Affinity Labels↗
PubMed1983

Actions of Ca2+ antagonists on the guinea-pig ileal myenteric plexus preparation.

The guinea-pig ileal myenteric plexus preparation has been used to compare the actions of three Ca2+ channel antagonists, D 600 (methoxyverapamil), nicardipine and diltiazem, on smooth muscle contractions and acetylcholine release in response to electrical stimulation. Acetylcholine release was not affected by these agents at concentrations of 10(-6)-10(-5)M. In confirmation of previous work, however, the smooth muscle contractile responses were effectively inhibited at these concentrations. Quercetin, a non-Ca2+ channel antagonist, was approximately equieffective in blocking both acetylcholine release and smooth muscle contractions. These data suggest that differences may exist in the antagonist sensitivity of voltage-dependent Ca2+ channels.

Animals↗
PubMed1983

Binding of the calcium channel blocker nitrendipine to its receptor in purified sarcolemma from canine cardiac ventricle.

High affinity binding of the 1,4-dihydropyridine calcium channel blocker [3H]nitrendipine was found in cardiac sarcolemma but not cardiac sarcoplasmic reticulum or mitochondria. Sarcolemmal binding of [3H]nitrendipine was saturable and reversible, with a maximum (Bmax) of approximately 1 pmol/mg protein and a Kd of approximately 0.14 nM. Displacement of sarcolemma-bound [3H]nitrendipine by other nifedipine analogs was stereospecific. The Kd for nitrendipine binding was approximately three orders of magnitude lower than the IC50 for the negative inotropic effect of this drug on isolated cat myocardium.

Animals↗
PubMed1983

The effects of erythrosin B(FD & C Red No. 3) on the guinea-pig ileum myenteric plexus-longitudinal muscle preparation.

The responses of the guinea-pig ileum myenteric plexus-longitudinal muscle to the food, drug and cosmetic dye erythrosin B (FD & C Red No. 3) were examined in acetylcholine- and electrically-stimulated preparations. Erythrosin B (10(-6)-10(-4)) reduced the amplitude of the mechanical responses produced by both stimuli. The effects were not simply concentration- and time-dependent. Responses to field stimulation were more sensitive to inhibition by erythrosin B, inhibition increasing with both concentration of dye and time of exposure. Responses to acetylcholine were generally less sensitive to erythrosin B and inhibition at 90 min exposure was more evident at lower concentrations of the dye. Many preparations contracted briefly upon exposure to low concentrations of the dye. Erythrosin B did not significantly affect the specific binding of [3H]QNB to muscarinic receptors. Erythrosin B reduced resting K+ levels in the longitudinal muscle but Na+ concentrations were essentially unaffected. Muscarinic agonist-stimulated uptake of Na+ and release of K+ were inhibited by erythrosin B (10(-6)-10(-4)M); this effect was enhanced with increased time of exposure to the dye. The effects of erythrosin B on cellular ion concentrations were more evident at low than at high concentrations of the dye. Erythrosin B reduced the efflux of [3H]acetylcholine induced by field stimulation from the myenteric plexus longitudinal muscle preparation.

Acetylcholine↗
PubMed1983

New developments in Ca2+ channel antagonists.

Toward the beginning of this Perspective we posed a number of questions to be answered concerning the Ca2+ channel antagonists. Biochemical, chemical, clinical, pharmacological, and physiological studies collectively support the conclusion that this important group of molecules does function in specific fashion to inhibit Ca2+ channel function. Major questions of mechanisms and sites of action remain, however, to be resolved. The recent radioligand binding assay supports the conclusion, drawn earlier from the chemical and pharmacological heterogeneity of these agents, that there exists multiple sites and mechanisms of action for the Ca2+ channel antagonists. This is a satisfying conclusion, since, although it makes high demands on future experimentation designed to delineate these sites and mechanisms, it indicates the very real possibility for the development of tissue-selective Ca2+ channel antagonists. Elsewhere in this review we have already addressed the question of tissue selectivity as observed for existing compounds. In our opinion, the structural and pharmacological clues available should bring us closer to the goal of second- and third-generation Ca2+ antagonists with defined tissue selectivity.

Animals↗
PubMed1983

Calcium, the control of smooth muscle function and bronchial hyperreactivity.

The Ca2+ requirements for excitation-contraction coupling in smooth muscle may be satisfied from both intracellular and extracellular sources, the relative extent of use of which is both tissue- and stimulant-dependent. Extracellular Ca2+ is apparently mobilized through two separate pathways, receptor operated (ROC) and potential dependent (PDC) Ca2+ channels. The latter process is sensitive to the Ca2+-channel antagonists, a heterogeneous group of compounds including verapamil, nifedipine and diltiazem. Ca2+ mobilization in respiratory smooth muscle is reviewed. The available evidence for this multiple stimulant-sensitive system indicates that both intra- and extracellular sources of Ca2+ are used. Data from bovine, canine and guinea pig tracheal muscle indicate, from studies of Ca2+-dependence of response and Ca2+ channel antagonist sensitivity, that the extent of use of extracellular Ca2+ lies in the order K+ greater than histamine greater than or equal to 5-hydroxytryptamine greater than acetylcholine. The bronchodilator activity of the Ca2+ channel antagonists is noted. Bronchial hyperreactivity is characterized by an increased sensitivity to a variety of stimulants including cold air, exercise, histamine and acetylcholine. The possible origins of this defect are noted. It is suggested that a defect in Ca2+ mobilization or in the receptor - Ca2+ mobilization coupling process at the level of the smooth muscle may constitute an important underlying cause of bronchial hyperreactivity. Potential analogies to reactivity changes seen in hypertensive vascular smooth muscle are noted.

Animals↗
PubMed1983

Demonstration of central nervous system tolerance to ethanol in mice: consequent effects on smooth muscle in vitro.

Mice were given ethanol (9 g/kg) or saline (57 ml/kg) daily in three divided doses for periods of 1 and 4 days to study the effects of such ethanol (ETOH) exposure on central nervous system (CNS) and peripheral smooth muscle (vasa deferentia) function. After 1 day, ETOH-treated mice were functionally tolerant to the hypothermic (3 g/kg, intraperitoneal), but not to the hypnotic (3.25 g/kg, intraperitoneal) effect of ETOH. Functional tolerance to both CNS effects of ETOH was demonstrated in mice after the 4-day ETOH exposure. Norepinephrine (NE) and high K+-depolarizing solutions each elicited dose-dependent contractions in the mouse vasa deferens preparation in vitro that consisted of a phasic and tonic component. The tonic components of the NE and K+ responses were more dependent upon extracellular Ca2+ (Ca2+ext) than the phasic components. Addition of ETOH (120 to 480 mM) or the Ca2+ channel-antagonist nifedipine (1 X 10(-9) to 3 X 10(-7) M) to the preparation selectively inhibited the tonic component of the NE and K+ responses, suggesting that both agents acted to inhibit the responses by interfering with the translocation of Ca2+ext. Vasa deferentia isolated from ETOH-treated mice did not exhibit altered reactivity to NE in the phasic or tonic component of the response. The isolated smooth muscle from mice centrally tolerant to ETOH did not appear to be tolerant to inhibitory effect of ETOH or cross-tolerant to the inhibitory effect of nifedipine on stimulant-induced contractions.

Animals↗
PubMed1983

The action of the ionophore ionomycin in guinea-pig intestinal smooth muscle.

The ionophore ionomycin produced concentration-dependent (5 X 10(-9) to 5 X 10(-6) M) contractions in guinea-pig ileal longitudinal smooth muscle. Responses were dependent on extracellular Ca2+, consistent with the known role of this Ca2+ source in supporting excitation-contraction coupling to a variety of stimulants in this tissue. Responses were insensitive to atropine (10(-6) M) but were dependent upon extracellular Na+ and were completely blocked by low concentrations of the Ca2+-channel antagonists nicardipine, YC-93 (5 X 10(-7) M), and D-600 (5 X 10(-6) M). The behaviour of ionomycin is very similar to that shown by A 23187 in this tissue. Ionomycin, like A 23187, can apparently activate D-600 sensitive Ca2+ channels in the guinea-pig intestinal smooth muscle rather than simply translocating Ca2+EXT.

Animals↗
PubMed1983

Inhibition by cinnarizine of the responses of smooth muscle from spontaneously hypertensive and normotensive rats.

A comparison was made of the inhibition by cinnarizine, a calcium antagonist, of the contractile responses of aortic, carotid, and iliac arterial strips and vasa deferentia from 15- to 17-week-old spontaneously hypertensive rats (SHR) and their normotensive counterparts, Wistar Kyoto (WKY) rats. KCl-induced responses of the aorta from both strains of rats and carotid arteries from WKY only were more sensitive to inhibition than were responses to norepinephrine. No significant differences were observed in the inhibition of tissue responses from the two strains of rats with the exception of the K+-induced responses of carotid arterial strips from SHR which were significantly less sensitive to inhibition when compared with carotid strips from WKY.

Animals↗
PubMed1983

Calcium antagonists. Some chemical-pharmacologic aspects.

Ca++ serves multiple roles as a regulator and initiator of cellular events. A variety of mechanisms serve to control cellular Ca++ levels and there exists a corresponding diversity of drugs which possess, with varying degrees of potency and selectivity, Ca++-antagonistic properties. Particular interest attaches to a group of agents designated as Ca++-channel or Ca++-entry blockers and includes verapamil, nifedipine, diltiazem, cinnarizine, and prenylamine. These agents function by blockade of the potential dependent Ca++-channel. However, their obvious chemical heterogeneity suggests that several sites and mechanisms of action may exist. A review of some basic questions concerning the action of the Ca++ channel antagonists is presented. The existence of discrete structure-activity relationships is consistent with the concept that these agents have specific sites of action, rather than serving, for example, as, nonspecific membrane-stabilizing agents. This view is further supported by their selectivity of action seen both in tissue selectivity and selectivity of antagonism of agonist responses. Studies of the relationship of these compounds to Ca++ show that they appear to function competitively against Ca++ and to block cellular Ca++ uptake. Moreover, both contractile responses and cellular Ca++ uptake appear equisensitive to these antagonists, providing further evidence that inhibition of Ca++ uptake underlies their inhibition of mechanical response. Of particular importance is the question of selectivity of action. It is quite clear that the Ca++ channel antagonists do not show equal activity toward all Ca++ channels and that major differences in selectivity occur between cardiac and smooth muscle. It is possible that selectivity of antagonism may occur between different vascular beds. Furthermore, Ca++ channels controlling stimulus-secretion coupling appear to be less sensitive to these antagonists than the channels involved in excitation-contraction coupling. Finally, the actions of Ca++ antagonists on non-Ca++-mediated processes, including Na+-dependent and receptor-binding events, are noted. These actions are seen at higher concentrations than those needed to inhibit Ca++ channel events, and their contribution to the therapeutic actions exerted by these antagonists is unknown.

Animals↗
PubMed1983

Characterization of binding of the Ca++ channel antagonist, [3H]nitrendipine, to guinea-pig ileal smooth muscle.

A chemically heterogeneous group of compounds, the Ca++ channel antagonists, which includes verapamil, diltiazem and nifedipine inhibits excitation-contraction coupling in smooth and cardiac muscle by blocking Ca+ entry at a specific class of Ca++ channels. The binding of the nifedipine analog, [3H]nitrendipine, to a microsomal fraction from guinea-pig longitudinal smooth muscle has been characterized. Specific binding was saturable, linear with protein concentration and reversible. The apparent equilibrium dissociation constant was 1.63 +/- 0.06 X 10(-10)M and the maximum site density was 1.13 +/- 0.03 pmol/mg of protein determined from Scatchard analysis of equilibrium binding at 25 degrees C. Inhibition of binding was specific and stereoselective for Ca++ channel antagonist drugs and was unaffected by a variety of receptor active ligands. Correlations between binding and inhibition of mechanical response to methylfurmethide- and K+-stimulation in a series of nifedipine analogs were determined. A 1:1 correlation was found for the K+ tonic response, but for the phasic component of the K+ response and for both components of the methylfurmethide response the antagonists were more active as inhibitors of [3H]nitrendipine binding than as inhibitors of mechanical response. [3H]Nitrendipine binding was sensitive to other Ca++ channel antagonists including verapamil, D-600, diltiazem, flunarizine, lidoflazine and bepridil. Interaction with these agents suggests, consistent with previous reports, that more than one binding site for Ca++ antagonists exists. A variety of inorganic divalent and trivalent cations (Mn++, Co++, Ni++, Pb++, UO2++, Zn++, Cd++, Cu++, Tm+++ and La+++) inhibit specific [3H]nitrendipine binding. The data suggest that [3H]nitrendipine binding in smooth muscle is to a site which mediates the pharmacologic response.

Animals↗
PubMed1983

Inhibition by concanavalin A, dansylcadaverine and bacitracin of muscarinic receptor-mediated desensitization in guinea-pig Ileal smooth muscle.

The muscarinic agonist, cis-2-methyl-4-dimethylaminomethyl-1,3-dioxolane methiodide (CD), and histamine desensitize the responses of guinea-pig ileal longitudinal smooth muscle to subsequently administered CD or histamine, respectively. Desensitization by CD, but not by histamine, was inhibited by concanavalin A (Con A) and this protection was prevented by co-administration of succinyl-Con A or by cytochalasin B or colchicine at concentrations which alone did not affect desensitization. Dansylcadaverine and bacitracin, inhibitors of transglutaminase, both protected against CD desensitization but were without effect on desensitization mediated by histamine. Benzilylcholine mustard, which reduced muscarinic receptor density, significantly reduced CD-induced desensitization. The effects of Con A and the transglutaminase inhibitors suggest that agonist-induced changes in muscarinic receptor distribution or receptor-effector coupling, via cytoskeletal and transglutaminase-sensitive mechanisms, are a component of CD-induced desensitization. These processes do not appear to be involved in histamine receptor-mediated desensitization. Although desensitization by CD or histamine is nonspecific in this preparation, both agonists cross-desensitizing, the effects of Con A, dansylcadaverine and bacitracin clearly indicate differences in the desensitization process elicited by these two stimulants.

Animals↗
PubMed1982

Binding of [3H]nimodipine to cardiac and smooth muscle membranes.

Specific binding of [3H]nimodipine to membranes from rat ventricle and guinea pig ileal longitudinal smooth muscle was studied. Dissociation constants were 0.24 and 0.12 nM, and the maximal number of binding sites were 0.4 and 0.75 pmol/mg protein for cardiac and smooth muscle, respectively. The values obtained for both types of muscle were similar to those obtained for [3H]nitrendipine binding, as were the potencies of a series of dihydropyridines for competing with [3H]nimodipine. These results support the hypothesis that the binding site characterized is that mediating the pharmacological effects of these compounds.

Animals↗