Guinea-pig Ileal Longitudinal Smooth Muscle Research Articles

Synthesis and calcium channel antagonist activity of 1,4-dihydropyridine derivatives containing 4-nitroimidazolyl substituents.

Alkyl, cycloalkyl and arylakyl ester analogues of nifedipine (CAS 21829-25-4), in which the ortho-nitro phenyl group at position 4 is replaced by 1-methyl-4-nitro-5-imidazolyl substituent, were synthesized and evaluated as calcium channel antagonists using the high K+ contraction of guinea-pig ileal longitudinal smooth muscle. The results for the symmetrical esters showed that increasing the length of methylene chain in C-3 and C-5 ester substituents for more than two methylene units (n > 1) decreases activity. In the phenylalkyl ester series increasing the length of methylene chain increases activity. In the series of unsymmetrical phenylalkyl esters (R2 = Me or Et) increasing the length of the methylene chain decreases activity. The results demonstrate that most of the compounds had similar activity to the reference drug nifedipine. Among symmetrical diesters (methyl, ethyl and phenylpropyl derivatives) and among unsymmetrical series (benzyl methyl, benzyl ethyl and phenethyl ethyl derivatives) were more active than the reference drug nifedipine. The unsymmetrical phenethyl ethyl derivative was the most potent antagonist tested. The structure-activity data indicate that the 4-(1-methyl-4-nitro-5-imidazolyl) moiety, bioisoester of 2-nitro-phenyl moiety, is as good as other nitro-imidazolyl moieties.

Synthesis and calcium channel antagonist activity of new 1,4-dihydropyridine derivatives containing dichloroimidazolyl substituents.

A group of dialkyl, dicycloalkyl and diaryl ester analogues of nifedipine (CAS 21829-25-4), in which the ortho-nitrophenyl group at position 4 is replaced by a 4,5-dichloroimidazolyl substituent, were synthesized and evaluated as calcium channel antagonists using the high K+ contraction of guinea-pig ileal longitudinal smooth muscle. The results for the symmetrical esters in alkyl esters series showed that increasing the length of the methylene chain in C3 and C5 ester substituents (from n = 0 to n = 2) increased the activity. When increasing of the length was accompanied by increase of the hindrance, the activity decreased. In the unsymmetrical diester series, the results showed when R1 is a small substituent (R1 = Me), increasing of the lipophilic property in R2 substituent increases the activity if this high lipophilicity is not accompanied by steric hindrance. The results demonstrate that in the unsymmetrical series, several compounds (benzyl methyl, benzyl isopropyl and cyclohexyl ethyl) had activity similar to that of the reference drug nifedipine. In symmetrical diesters compounds, the most active compound was the diphenethyl ester derivative being more active than nifedipine. These structure-activity data indicate that the 4-(4,5-dichloroimidazolyl) moiety is the bioisoester of 3-nitrophenyl and 2,3-dichlorophenyl moieties.

Design and synthesis of new 1,4-dihydropyridines containing 4(5)-chloro-5(4)-imidazolyl substituent as a novel calcium channel blocker

New analogues of nifedipine, in which the ortho-nitro phenyl group at position 4 has been replaced by 4(5)-chloro-5(4)-imidazolyl substituent and which are able to interact with the receptor by hydrogen binding were designed, synthesized, and evaluated as calcium channel antagonists. The designed dihydropyridines were synthesized using the Hantzsch condensation and evaluated as calcium channel antagonists using the high K+ contraction of guineapig ileal longitudinal smooth muscle. A docking study was performed using the AutoDock4 program, and QSAR equations were obtained using multilinear regression. Our computational studies indicated that the oxygen of the ester (O10) and the N3' of the imidazole ring form a hydrogen bonding interaction with the NH of HIS 363 and NH of LYS354, respectively, and that the sum of the BEHp5 and RDF075p are the most significant descriptors. The results of calcium channel antagonist evaluation demonstrated that increasing the chain length in C3 and C5 ester substituents increased activity. The most potent compound was the bis-phenylpropyl ester (5l) derivative, in that it was more active than the reference drug nifedipine and that the bis-phenylethyl ester (5k) derivative had comparable activity with nifedipine. The present research revealed that the 4(5)-chloro-5(4)-imidazolyl moiety is a bioisoster of o-nitrophenyl in nifedipine and provided novel dihydropyridines with more activity as calcium channel antagonists.

SYNTHESIS AND CALCIUM-CHANNEL ANTAGONIST ACTIVITY OF NIFEDIPINE ANALOGUES CONTAINING NITROIMIDAZOLYL SUBSTITUENT IN GUINEA-PIG SMOOTH ILEAL MUSCLE

Alkyl, cycloalkyl or aryl ester analogues of nifedipine, in which the ortho-nitrophenyl group at position 4 is replaced by 1-methyl-5-nitro-2-imidazolyl substituent, were synthesized and evaluated as calcium-channel antagonists using the high K+ contraction of guinea-pig ileal longitudinal smooth muscle. The results for the symmetrical esters showed that increasing the length of methylene chain (n > 2) decreases activity. The relative activity profile for asymmetrical esters was cyclopentyl > cyclohexyl > cyclopropyl. Comparison of esters having the same methylene space showed that the cyclohexyl compounds were more active than the corresponding phenyl derivatives. In addition, asymmetrical esters possessing one R2 substituent (methyl > ethyl) indicated that increasing the length of methylene chain in the R1-substituent decreased activity. Our results demonstrate that several compounds were more active than the reference drug nifedipine. The symmetrical cyclohexyl ester (n = 0) and the asymmetrical (R1 = cyclohexyl, R2 = Me, n = 0) derivatives were the most potent antagonists tested.

Synthesis of alkyl 6‐methyl‐4‐(2‐pyridyl)‐1,2,3,4‐tetrahydro‐2H‐pyrimidine‐2‐one‐5‐carboxylates for evaluation as calcium channel antagonists

Abstractmagnified imageThe Bigenelli acid catalyzed condensation of 2‐pyridylcarboxaldehyde (1), urea (2) and an alkyl acetoacetate (3) afforded the respective alkyl (Me, Et, i‐Pr, i‐Bu, t‐Bu) 6‐methyl‐4‐(2‐pyridyl)‐1,2,3,4‐tetrahydro‐2H‐pyrimidine‐2‐one‐5‐carboxylates (4a‐e). The most potent calcium channel antagonist ethyl 6‐methyl‐4‐(2‐pyridyl)‐1,2,3,4‐tetrahydro‐2H‐pyrimidine‐2‐one‐5‐carboxylate (4b, IC50 = 1.67 × 10−5 M) wasa much weaker calcium channel antagonist than the reference drug nifedipine (Adalat®, IC50 = 1.40 × 10−8 M) on guinea pig ileal longitudinal smooth muscle (GPILSM). The alkyl 6‐methyl‐4‐(2‐pyridyl)‐1,2,3,4‐tetrahydro‐2H‐pyrimidine‐2‐one‐5‐carboxylates did not show any inotropic effect on heart since no increase, or decrease, in the contractile force of guinea pig left atrium was observed. These structure activity studies show that the alkyl 6‐methyl‐4‐(2‐pyridyl)‐1,2,3,4‐tetrahydro‐2H‐pyrimidine‐2‐one‐5‐carboxylates (4a‐e) are partial bioisosteres of nifedipine with respect to calcium channel antagonist activity on guinea pig ileal longitudinal smooth muscle (GPILSM).

Synthesis, study of 3D structures, and pharmacological activities of lipophilic nitroimidazolyl-1,4-dihydropyridines as calcium channel antagonist

QSAR studies indicated that the potency of nifedipine analogues was dependent upon lipophilicity, an electronic term and separated terms for each position on the DHP ring. Changes in the substitution pattern at the C 3, C 4, and C 5 positions of DHPs alter potency, tissue selectivity, and the conformation of the 1,4-DHP ring. In this project a group of alkyl ester analogues of new derivatives of nifedipine, in which the ortho-nitrophenyl group at position 4 is replaced by a 1-methyl-5-nitro-2-imidazolyl substituent, and the methyl group at position 6 is replaced by a phenyl substituent, were synthesized and evaluated as calcium channel antagonist using the high K + contraction of guinea-pig ileal longitudinal smooth muscle. The results for asymmetrical esters showed that lengthening of the substituent in C 3 ester substituent increased activity. When increasing of the length is accompanied by increasing the hindrance, the activity decreased. The results demonstrate that all compounds were more active or similar in effect to that of the reference drug nifedipine.

Lipophilic 4-imidazoly-1,4-dihydropyridines: synthesis, calcium channel antagonist activity and protection against pentylenetetrazole-induced seizure

A group of alkyl, cycloalkyl and aryl ester analogs of nifedipine, in which the o-nitrophenyl group at position 4 is replaced by a 2-phenyl-4(5)-imidazolyl substituent, were synthesized and evaluated as calcium channel antagonist using the high K + contraction of guinea-pig ileal longitudinal smooth muscle, and the activity of 5a–d, 8b and 8f against pentylenetetrazole (PTZ)-induced seizure was assessed. The results for symmetrical esters showed that lengthening of the methylene chain in C 3 and C 5 ester substituents increased activity. When increasing of the length is accompanied by increasing the hindrance, the activity decreased. In contrast to symmetrical derivatives, comparison of the activities of asymmetrical esters showed that increasing the length of the methylene chain was accompanied by a decrease in their activity. The results demonstrate that 8a was more active, and 5c and 8f were similar in effect to that of the reference drug nifedipine. The time-course of anticonvulsant effect on PTZ-induced seizure threshold of said compounds was assessed and showed that increasing the lipophilicity decreases the time needed for maximum effect. Mice treated with intraperitoneal injection of 25 mg/kg of these derivatives all exhibited increase seizure threshold as compared with control.

Synthesis and Calcium Antagonist Activity of 1,4‐Dihydropyridines Containing Phenylaminoimidazolyl Substituents.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and calcium antagonist activity of 1,4-dihydropyridines containing phenylaminoimidazolyl substituents

Alkyl ester analogues of nifedipine, in which the ortho-nitrophenyl group at position 4 is replaced by 2-methylthio-1-phenylamino-5-imidazolyl substituent, were synthesized and evaluated as calcium-channel antagonists using the high K + contraction of guinea-pig ileal longitudinal smooth muscle. The results for the symmetrical esters showed that in the series of alkyl esters increasing the length of methylene chain in C-3 and C-5 ester substituents for more than two methylene units decreases activity. In the phenylalkyl ester series increasing the length of methylene chain also decreases activity. The results demonstrate that most of the compounds had similar activity to the reference drug nifedipine. In addition, two compounds, 5b and 5f were more active than the nifedipine.

Effects of G-protein-specific antibodies and G beta gamma subunits on the muscarinic receptor-operated cation current in guinea-pig ileal smooth muscle cells.

(1) The effects on the whole-cell carbachol-induced muscarinic cationic current (mIcat) of antibodies against the alpha-subunits of various G proteins, as well as the effect of a Gbetagamma subunit, were studied in single guinea-pig ileal smooth muscle cells voltage-clamped at -50 mV. Ionized intracellular calcium concentration, [Ca(2+)](i), was clamped at 100 nM using a 1,2-bis(2-aminophenoxyl-ethane-N,N,N',N'-tetraacetic acid)/Ca(2+) mixture. (2) Application of ascending concentrations of carbachol (1-300 micro M) activated mIcat (mean amplitude 0.83 nA at 300 micro M carbachol; EC(50) 8 micro M; Hill slope 1.0). A 20 min or longer intracellular application via the pipette solution of G(i3)/G(o) or G(o) antibodies resulted in about a 70% depression of the maximum response without change in the EC(50) value. In contrast, antibodies against alpha-subunits of G(i1), G(i1)/G(i2), G(i3), G(q)/G(11) or G(s) protein over a similar or longer period did not significantly reduce mIcat. Antibodies to common Gbeta or infusion of the Gbetagamma subunit itself had no effect on mIcat. (3) If cells were exposed briefly to carbachol (50 or 100 micro M) at early times (<3 min) after infusion of antibodies to Galpha(i3)/Galpha(o) or to Galpha(o) had begun, carbachol responses remained unchanged even after 20-60 min; that is, the depression of mIcat by these antibodies was prevented. (4) These data show that Galpha(o) protein couples the muscarinic receptor to the cationic channel in guinea-pig ileal longitudinal smooth muscle and that Gbetagamma is not involved. They also show that prior activation of the muscarinic receptor presumably causes a long-lasting postactivation change of the G protein, which is not reflected in mIcat, but acts to hinder antibody binding.

Synthesis and Calcium Channel Antagonist Activity of 1,4‐Dihydropyridine Derivatives Containing 4‐Nitroimidazolyl Substituents.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The novel heteromeric bivalent ligand SB9 potently antagonizes P2Y 1 receptor-mediated responses

Effects of 6-[(4,6,8-trisulfo-1-naphthyl)iminocarbonyl-1,3-(4-methylphenylene)iminocarbonyl-1,3-phenylene-azo]-pyridoxal-5′-phosphate (SB9), a heterodimeric bivalent ligand consisting of pyridoxal-5′-phosphate and the suramin monomer, were studied on contractions of the rat vas deferens elicited by αβ-methylene ATP (αβmeATP; mediated by P2X 1-like receptors), contractions of the guinea-pig ileal longitudinal smooth muscle elicited by adenosine 5′- O-(2-thiodiphosphate) (ADPβS; mediated by P2Y 1-like receptors), and the degradation of ATP by ecto-nucleotidases in folliculated Xenopus laevis oocytes. SB9 (0.1–10 μM) antagonized contractile responses produced by αβmeATP or ADPβS in a concentration-dependent manner. Schild analysis yielded linear regression lines of unit slope, indicating competitive antagonism. From the rightward shifts of the agonist concentration–response curves p A 2 values of 6.05±0.13 (vas deferens) and 6.98±0.07 (ileum) were derived. In both preparations, SB9 behaved as a slow onset, slow offset antagonist. Incubation of three oocytes in the presence of ATP produced an increase in inorganic phosphate (P i) over a 30-min period, which amounted to 35.1±1.9 μM P i from 100 μM ATP. SB9 (10–1000 μM) reduced this degradation (pIC 50=4.33±0.10). The results illustrate that SB9 is a high-affinity P2Y 1 receptor antagonist with a remarkable selectivity for P2Y 1 vs. P2X 1 receptors (about 10-fold) and ecto-nucleotidases (447-fold). These properties make it unique among the pyridoxal-5′-phosphate and suramin derivatives reported to date.

Design and syntheses of C‐4 4‐(1‐methoxycarbonyl‐1,2‐dihydropyridyl)‐, and 3‐[1‐methoxycarbonyl‐1,2‐(and 1,6‐)dihydropyridyl]‐, derivatives of alkyl 1,4‐dihydro‐2,6‐dimethyl‐3‐nitro‐5‐pyridinecarboxylates with cardiospecific calcium channel agonist activity

A group of hitherto unknown alkyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(dihydropyridyl)-5-pyridinecarboxylates possessing 4-[4-(1-methoxycarbonyl-1,2--dihydropyridyl)]- (6-10), or 4-[3-(1-methoxycarbonyl-1,2-(and 1,6-)dihydropyridyl)]- (16-20), moieties were synthesized by reaction of the 4-(4-pyridyl)- (1-5), or 4-(3-pyridyl)- (11-15), precursors with methyl chloroformate in the presence of sodium borohydride. In vitro calcium channel (CC) antagonist activities were determined using a muscarinic-receptor-mediated Ca 2+ -dependent contraction of guinea pig ileal longitudinal smooth muscle (GPILSM) assay. Elaboration of the 4-pyridyl (1-5), or 3-pyridyl (11-16), substituent to the corresponding 1,2-(1,6)dihydropyridyl moiety abolished the CC agonist effect produced by 1-5 and 11-15 on GPILSM. In addition, all alkyl esters possessing a 4-[4- or 3-(1-methoxycarbonyl-1,2--(1,6-)dihydropyridyl)]- moiety (6-10, 17, 19-20) were inactive CC antagonists on GPILSM with the exception of the ethyl (16) and isobutyl (18) ester derivatives, which exhibited weak CC antagonist activity. All of the 4-[4- or 3-(1-methoxycarbonyl-1,2-(1,6-)dihydropyridyl)] compounds evaluated (6-10, 16-19) exhibited in vitro CC agonist (positive inotropes) activity on guinea pig left atria (GPLA). In general, the 4-[3-(1-methoxycarbonyl-1,2-(and 1,6)dihydropyridyl)] compounds (16-19) were more potent CC agonists (EC 50 = 2.91 × 10 -6 to 7.51 x 10 -6 M range) than the corresponding 4-[4-(1-methoxycarbonyl-1,2-dihydropyridyl)] compounds (6-9, EC 50 = 1.42 x 10 -5 to 2.65 x 10 -5 M range). These 4-[4- or 3-(1-methoxycarbonyl-1,2-(1,6)dihydropyridyl)] compounds, which exhibit cardiospecific CC agonist activity (6-10, 17, 19) will serve as valuable model compounds to study the structure-function relationships of CC modulation, and provide a new drug design concept directed toward the treatment of congestive heart failure.

SYNTHESIS AND CALCIUM-CHANNEL ANTAGONIST ACTIVITY OF 4- IMIDAZOLYL-1,4-DIHYDROPYRIDINES

The o-nitrophenyl group at position 4 of dihydropyridine of nifedipine analogues was replaced by 1-methylimidazole. These compounds were evaluated as calcium-channel antagonists using the high K+ contraction of guinea-pig ileal longitudinal smooth muscle. The results for the symmetrical esters showed that increasing the length of methylene chain of ester more than 3 units decreases activity. For cyclic esters, cyclopropylmethyl ester was more active than cyclohexylmethyl ester. Our results revealed two compounds with activities similar to the reference drug nifedipine; the symmetrical cyclopropylmethyl ester, and the asymmetrical phenethyl ethyl derivatives were the most potent antagonists tested.

Characterization of the interaction between muscarinic M2 receptors and β‐adrenoceptor subtypes in guinea‐pig isolated ileum

1. Contraction of guinea-pig ileum to muscarinic agonists is mediated by M3 receptors, even though they account for only 30% of the total muscarinic receptor population. The aim of this study was to characterize the biochemical and functional effects of stimulation of the predominant M2 muscarinic receptor (70%) and to investigate the hypothesis that M2 receptors specifically oppose beta-adrenoceptor-mediated effects in the ileum. 2. In guinea-pig ileal longitudinal smooth muscle slices, isoprenaline, a non-selective beta-adrenoceptor agonist, and BRL 37344 (sodium-4-[2-[2-hydroxy-2-(3- chlorophenyl)ethylamino]propyl]-phenoxyacetate sesquihydrate), a beta 3-adrenoceptor selective agonist, increased cyclic AMP accumulation with -log EC50 values of 6.6 +/- 0.1 and 5.8 +/- 0.1 respectively. Maximal stimulation by BRL 37344 (10 microM) was 26.4 +/- 5.2% of that observed with isoprenaline (10 microM). Isoprenaline (10 microM)-stimulated cyclic AMP accumulation was significantly, but not completely, inhibited by propranolol (5 microM), with a propranolol-resistant component of 28.2 +/- 6.8% of the maximal stimulation to isoprenaline. In contrast, basal and BRL 37344 responses were resistant to this antagonist. These data provide evidence that both beta 1- and beta 3-adrenoceptors activate adenylyl cyclase in guinea-pig ileum. 3. Isoprenaline (10 microM)-stimulated cyclic AMP accumulation was inhibited (67.4 +/- 0.9%) by the muscarinic agonist (+)-cis-dioxolane (-log EC50 = 7.3 +/- 0.1). The rank order of antagonist affinities against the (+)-cis-dioxolane response was (-log KB values in parentheses): atropine (9.0 +/- 0.2)>methoctramine (7.1 +/- 0.1) >p-fluoro-hexa-hydrosilaphenidol (p-F-HHSiD; 6.5 +/- 0.2) ) pirenzepine(6.3 +/- 0.2). (+)-cis-dioxolane also significantly inhibited BRL 37344 (10 IM; 56.5 +/-2.4%) stimulated cyclic AMP accumulation. These data suggest that M2 receptors mediate inhibition of cyclic AMP accumulation in response to both beta l- and beta 3-adrenoceptor stimulation in guinea-pig ileum.4. 5-Hydroxytryptamine (5-HT), vasoactive intestinal peptide, prostaglandins E2 and E1, all at 10 micro M,significantly increased cyclic AMP accumulation. (+)-cis-Dioxolane (10 micro M) inhibited both basal and agonist-induced cyclic AMP accumulation. Thus the inhibitory effect of M2 receptor agonism does not appear to be restricted to beta-adrenoceptor-stimulated cyclic AMP accumulation.5. The potential for involvement of activation of M2 receptors on responses to beta-adrenoceptor agonists was also studied functionally. Selective M3 receptor alkylation was achieved by pretreatment of tissues with 4-DAMP mustard (40 nM), in the presence of methoctramine (1 micro M; to protect M2 receptors). After washing, tissues were pre-contracted with histamine (0.3 micro M) and relaxed with isoprenaline (0.6 micro M).Under these conditions, oxotremorine M caused concentration-dependent contractions (-log EC50 of 7.8 +/- 0.1), that were surmountably antagonized by methoctramine (1 microM) with a - log KB estimate of 7.4 +/- 0.1. Similar observations were seen versus relaxation produced by BRL 37344 (1 micro M), where the-log KB value for methoctramine was 7.8 +/- 0.2. These data suggest that M2 receptors mediate a functional inhibition of relaxant responses to isoprenaline and BRL 37344.6. These findings are consistent with beta l- and beta 3-adrenoceptors coupling to stimulation of a denylylcyclase in guinea-pig ileum; a response that is inhibited by M2 receptor stimulation. Concordantly, M2 receptor stimulation also inhibits relaxation to both beta l- and beta 3-adrenoceptor stimulation. These results implicate M2 receptors in the modulation of sympathetic control of ileal motility.

Effect of hydrogen peroxide on guinea-pig ileal longitudinal smooth muscle contractility

Effect of hydrogen peroxide on guinea-pig ileal longitudinal smooth muscle contractility

Evidence for the presence of two types of P 2 purinoceptor in the guinea-pig ileal longitudinal smooth muscle preparation

The effects of some agonists acting at P 2 purinoceptors on guinea-pig isolated ileum longitudinal smooth muscle have been examined. The preparation contracted in response to ATP, α,β-methylene ATP and 2-methylthio ATP, but not UTP. In this respect, α,β-methylene ATP and 2-methylthio ATP were approximately equipotent and both were 10–50 times more active than ATP. Responses to α,β-methylene ATP, but not 2-methylthio ATP or ATP, were antagonised by atropine and tetrodotoxin, suggesting that α,β-methylene ATP activates cholinergic nerves in the ileum, whilst the other two compounds act on the smooth muscle. Two other purine nucleotide analogues, β,γ-methylene ATP and β,γ-imido ATP, did not cause contraction. However, both compounds antagonised responses to α,β-methylene ATP, but not those to 2-methylthio ATP. Suramin antagonised responses to both α,β-methylene ATP and 2-methylthio ATP, whilst Cibacron blue was without effect on responses to either agonist. We conclude that the purinoceptor on cholinergic nerves has some of the characteristics of the P 2x purinoceptor, whilst the purinoceptor on ileal smooth muscle has some of the characteristics of the P 2Y purinoceptor. However, further work will be necessary before definitive classification is possible.

Characterization of intestinal smooth muscle responses and binding sites for endothelin.

The contractile activity of and binding sites for endothelin-1 (ET-1) were investigated in isolated guinea-pig ileal longitudinal smooth muscle (GPILM). ET-1 produced concentration-dependent contractions of GPILM that either slowly subsided in the continued presence of ET-1 or rapidly subsided following washing of the tissue. The ED50 value for ET-1 contractions was 4.2 +/- 1.3 x 10(-9) M. The removal of extracellular calcium or pretreatment with nifedipine produced a complete inhibition of the contractions to ET-1. The IC50 value of nifedipine for inhibition of ET-1 mediated contractions was 3.0 +/- 0.8 x 10(-8) M. ET-1 produced a marked prolonged homologous desensitization of its contractile response but did not affect the responses mediated by carbachol, histamine, serotonin, substance P, and PLA2. High-affinity binding sites for 125I-labelled ET-1 were identified on microsomal membranes prepared from GPILM with Kd and Bmax values obtained by Scatchard analysis of 3.5 +/- 0.6 x 10(-10) M and 2138 +/- 159 fmol/mg protein, respectively. The binding of 125I-labelled ET-1 to GPILM microsomes was characterized by a rapid association (kob value of 0.077 min-1 at a radioligand concentration of 0.45 nM and an extremely slow dissociation (k1 value of 0.011 min-1; t1/2 value of 793 min). The binding was unaffected by the calcium channel antagonists nifedipine, verapamil, and diltiazem (10(-6) M); the receptor antagonists phenoxybenzamine, atropine, and naloxone (10(-6) M) and propranolol; and the peripheral benzodiazepine receptor antagonists Ro 5-4864 and PK 11195 and psychotomimetic drug phencyclidine (10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)

P-293 - Inhibition of contraction and glucose utility of the guinea-pig ileal longitudinal smooth muscle in high K+, Na+ deficient solution

P-293 - Inhibition of contraction and glucose utility of the guinea-pig ileal longitudinal smooth muscle in high K+, Na+ deficient solution

Characterization of the effects of AHN 086, an irreversible ligand of "peripheral" benzodiazepine receptors, on contraction in guinea-pig atria and ileal longitudinal smooth muscle

The effects of AHN 086 and its reversibly acting structural analogue Ro 5-4864 were studied in the spontaneously beating guinea-pig atria and field-stimulated guinea-pig ileal longitudinal smooth muscle in the presence and absence of dihydropyridine calcium channel modulators. The treatment of guinea-pig atria with AHN 086 followed by extensive washing did not alter contraction. However, AHN 086 (0.5 microM) potentiated (88%) the positive inotropic responses by BAY K 8644, an effect that was not reversed by extensive washing of the tissue. Higher concentrations of AHN 086 (greater than 2 microM) irreversibly inhibited the intropic, but not the chronotropic responses to BAY K 8644, nifedipine, and isoproterenol. Ro 5-4864 (10 microM) produced a reversible enhancement of the inotropic responses and block of the chronotropic responses to BAY K 8644. In guinea-pig ileal longitudinal smooth muscle, both AHN 086 and Ro 5-4864 reversibly inhibited field-stimulated contractions. Neither Ro 5-4864 nor AHN 086 affected the ability of nifedipine to inhibit field-stimulated contractions of ileal longitudinal smooth muscle. Treatment of intact atrial with 5 microM AHN 086 followed by extensive washing resulted in a significant inhibition (30-50%) of [3H]Ro 5-4864 binding to peripheral benzodiazepine receptors and of [3H]nitrendipine binding to voltage-operated calcium channels, but did not affect [3H]dihydroalprenolol binding to beta-adrenergic receptors on atrial membranes. The same treatment applied to intact ileal longitudinal smooth muscle affected neither [3H] (-)-quinuclidinyl benzilate binding to muscarine receptors nor [3H]nitrendipine binding, but did result in a significant inhibition (30-50%) of [3H]Ro 5-4864 binding to ileal longitudinal smooth muscle membranes.(ABSTRACT TRUNCATED AT 250 WORDS)