Channel Opening Activity Research Articles

The discovery of a new class of large-conductance Ca2+-activated K+ channel opener targeted for overactive bladder: synthesis and structure-activity relationships of 2-amino-4-azaindoles.

2-Amino-4-azaindoles have been identified as a structurally novel class of BK(Ca) channel openers. Their synthesis from 2-chloro-3-nitropyridine is described together with their in vitro properties assessed by 86Rb(+) efflux and whole-cell patch-clamp assays using HEK293 cells stably transfected with the BK(Ca) alpha subunit. In vitro functional characterization of BK(Ca) channel opening activity was also assessed by measurement of relaxation of smooth muscle tissue strips obtained from Landrace pig bladders. The preliminary SAR data indicate the importance of steric bulk around the 2-amino substituent.

N-Arylated pyrrolidin-2-ones and morpholin-3-ones as potassium channel openers

Based on the most stable conformation of ZD6169, a series of N-arylated derivatives of oxazolidindione ( 2), morpholin-3-one ( 3– 5), piperidin-2-one ( 6), and pyrrolidin-2-one ( 7– 13) was synthesized and evaluated for potassium channel opening activity. In the in-vitro assays, N-(4-benzoylphenyl)-piperidin-2-one ( 6) and N-(4-benzoylphenyl)-3,3-dimethyl-pyrrolidin-2-one ( 9) demonstrated potent and selective relaxant activity at the bladder detrusor muscle [IC 50, bladder=7.4 and 6.7 μM, respectively; IC 50 ratio (portal vein/bladder)=41 and 51, respectively].

KMUP 880708: A vanyllilamide‐based β1‐adrenoceptor antagonist with α‐adrenoceptor blocking and potassium channel opening activities

AbstractA vanillylamide‐based propanolamine derivative, KMUP 880708, was first investigated both in vivo and in vitro. KMUP 880708 (0.1, 0.5, 1.0, and 2.0 mg kg–1, iv) produced dose‐dependent hypotensive and bradycardia responses in pentobarbital‐anesthetized Wistar rats. KMUP 880708 (0.1, 0.5, and 1.0 mg kg–1, iv) also markedly inhibited both the tachycardia effects induced by (–)isoproterenol and arterial pressor responses induced by phenylephrine. KMUP 880708 competitively antagonized (–)isoproterenol‐induced positive inotropic and chronotropic effects of the atria and tracheal relaxation responses on isolated guinea pig tissues. The apparent pA2 values for KMUP 880708 was 7.82 ± 0.06 in the right atria, 7.51 ± 0.13 in the left atria, and 6.31 ± 0.07 in the trachea, respectively, indicating that KMUP 880708 was selective β1‐adrenoceptor blocker. In thoracic aorta experiments, KMUP 880708 also produced a competitive antagonism of norepinephrine‐induced contraction with pA2 value of 7.92 ± 0.52, indicating that KMUP 880708 was α‐adrenoceptor antagonist. In isolated rat thoracic aorta, KMUP 880708 more potently relaxed the contractions induced by phenylephrine (10–5 M) than those by high K+ (75 mM). KMUP 880708‐induced relaxation was significantly reduced by endothelium removal and by exposure to L‐NG‐nitro arginine methyl ester (L‐NAME, 1 and 3 × 10–4 M), indomethacin (3 × 10–5 M), methylene blue (10–5 M) and 1H‐[1,2,4]oxadiazolol[4,3,‐a]quinoxalin‐1‐one (ODQ, 10–6 M). The vasorelaxant effect of KMUP 880708 on phenylephrine‐induced contraction was attenuated by the pretreatment with tetraethylammonium (TEA), glibenclamide, charybdotoxin, and apamin, but not by 4‐aminopyridine (4‐AP). In addition, KMUP 880708 inhibited phenylephrine‐induced biphasic contraction and affected the fast‐twitch phase more significantly than the slow tonic phase. In the radioligand‐binding assay, the Ki values of [3H]CGP‐12177 binding to rat ventricle and lung membranes were 15.14 and 524.81 nM, respectively, and the value of [3H]prazosin binding to rat brain membrane was 3.89 nM. The ranking order of inhibition for [3H]CGP‐12177 binding on β‐adrenoceptor was propranolol > labetalol > KMUP 880708 > atenolol, and that for [3H]prazosin binding to α‐adrenoceptor was KMUP 880708 > labetalol. In conclusion, KMUP 880708 was found to be a new generation α/β‐adrenoceptor blocker with selective β1‐adrenoceptor blocking and vascular smooth muscle relaxation activities. Furthermore, the vasodilator effect of KMUP 880708 is attributed to the release of NO or NO‐related substance from vascular endothelium. While the endothelium‐independent mechanism involved in the relaxation of KMUP 880708 is probably linked to K+ channel activation in these vessels. Drug Dev. Res. 55:104–117, 2002. © 2002 Wiley‐Liss, Inc.

ChemInform Abstract: Synthesis and Potassium Channel Opening Activity of Substituted 10H‐Benzo[4,5]furo[3,2‐b]indole‐ and 5,10‐Dihydro‐indeno[1,2‐b]indole‐1‐carboxylic Acids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Levosimendan is a mitochondrial K ATP channel opener

Levosimendan, a new inodilator developed for the treatment of heart failure has been shown to have a vasodilatory effect via opening of K ATP channels in the plasma membrane of vascular smooth muscle cells. In this study, we investigated the effects of levosimendan on the mitochondrial K ATP channel. This compound did not influence mitochondrial transmembrane potential (Δ Ψ), and at up to 2.2 μM had no effect on the respiration rate of rat liver mitochondria, respiring on 5 mM succinate (+5 μM rotenone). A sensitive method was developed for assessing K ATP channel opening activity employing rat liver mitochondria, respiring only on endogenous substrates in the presence of 400 μM ATP and 1 μg oligomycin/mg mitochondrial protein. In this model, levosimendan (0.7–2.6 μM) decreased Δ Ψ by 6.5–40.4% ( n=3, incubation time 15 min). This effect was dependent on the K + concentration in the incubation medium and was abolished by the selective blocker of the mitochondrial K ATP channel-5-hydroxydecanoate (200 μM). Our results indicate that levosimendan opens mitochondrial K ATP channels.

Synthesis and potassium channel opening activity of substituted 10 H-Benzo [4,5]furo[3,2- b]indole- and 5,10-Dihydro-indeno[1,2- b]indole-1-carboxylic acids

Compounds in a structurally novel series of substituted 10 H-benzo[4,5]furo[3,2- b]indole-1-carboxylic acids and related 5,10-dihydro-indeno[1,2- b]indole-1-carboxylic acids were prepared and shown to possess potent, bladder-selective smooth muscle relaxant properties and thus are potentially useful for the treatment of urge urinary incontinence. Electrophysiological studies using rat detrusor myocytes have demonstrated that prototype compound 7 produces a significant increase in hyperpolarizing current, which is iberiotoxin (IbTx)-reversed, thus consistent with activation of the large-conductance Ca 2+-activated potassium channel (BK Ca).

Studies on the chemistry of thienoannelated O,N- and S,N-containing heterocycles. Part 19: thieno[2,3-b][1,4]thiazines with calcium antagonistic and potassium opening activities.

In this study novel substituted 6-benzyl-thieno[2,3-b][1,4]thiazines with an urea moiety were synthesized. Structural modifications of the amino side chain were carried out with the aim of finding tissue specific compounds. The effects on papillary muscles, right atria, aortic strips, and terminal ilea were investigated. Compounds 10c and 10d showed the most potent negative inotropic effect. The calcium antagonism of all derivatives occurred in a non-competitive manner, which may indicate that they also have potassium channel opening activities.

Effects of an ATP-sensitive potassium channel opener, YM934, on hypoxia/reoxygenation injury of isolated canine cardiac cells

The cardioprotective effects of YM934, an ATP-sensitive potassium channel opener (KCO), on isolated canine cardiomyocytes were examined. Exposure of isolated canine cardiomyocytes to YM934 (10 μM) resulted in an increase of potassium channel opening activity in whole cell patch clamp technique. Glibenclamide (1 μM) reversed the channel opening activity induced by YM934. Pretreatment of the cardiomyocytes with YM934 caused a potent inhibition KCL (20 mM)-induced increase in [Ca2+]i. Cromakalim also inhibited the KCL-induced increase in [Ca2+]i under the same experimental conditions. The ratio of alive to dead cells and the release of creatine kinase from isolated cardiomyocytes during a 120-min hypoxia / 15-min reoxygenation period were dose-dependently (YM934; 0.1–10 μM) attenuated; 71–93% of the preischemic value for the ratio of alive/dead cells and 76–58% of the nontreated hearts for the release of creatine kinase. These results suggest that YM934 has a direct cardioprotective effect against ischemia/reperfusion injury of canine cardiac myocytes, possibly through opening ATP-sensitive potassium channels. Drug Dev. Res. 48:113–120, 1999. © 1999 Wiley-Liss, Inc.

Structure–activity relationships of new thienothiazine derivatives in isolated heart and smooth muscle preparations of guinea pigs

New thienothiazine derivatives that differ in their side chains on the nitrogen atom of the thienothiazine ring were investigated regarding structure–activity relationships and calcium antagonistic and/or potassium channel opening properties. Isometric contraction force was measured in guinea pig papillary muscles, aortic strips, and terminal ilea. Chronotropic activity was studied in right atria of guinea pigs. The derivatives with a dimethylaminoethylcarboxamide side chain (HO 4) and with a dimethoxyphenylethyl-N-methylaminoethylcarboxamide side chain (HO 7) had the most potent negative inotropic effects on papillary muscles and spontaneously beating right atria. The negative inotropic and chronotropic effects of the compounds with a methylpiperazinylcarbonyl side chain (HO 5) or a diethylaminopropylcarboxamide side chain (HO 6) were less pronounced. The negative inotropic action was reversed by increasing the extracellular calcium concentration. It was also reversed by glibenclamide, for concentrations of the compounds up to the EC 50, but not at higher compound concentrations. Among all the compounds studied, HO 7 had the strongest relaxing effect on aortic strips and terminal ilea. The effects of the derivatives on the smooth muscles could not be reversed by glibenclamide. The calcium antagonistic effect of the thienothiazine derivatives is more pronounced than the potassium channel opening activity, at least in high drug concentrations. Compounds with an aromatic or heterocyclic ring in the side chain have the weakest negative inotropic and negative chronotropic effects on papillary muscles and right atria. However, HO 7 showed a tissue specifity with the most potent relaxing effect on aortic strips and terminal ilea.

Effect of K+ Channel Openers, KRN2391 and Ki1769, and Nitroglycerin on the Urinary Tract of Rats In Vivo

The effects of KRN2391 (N-cyano-N’-(nitroxyethyl)-3-pyridine carboximidamide methanesulfonate), which possesses ATP-sensitive potassium (K+) channel opening (KCO) activity and nitrate activity; Ki1769 (N-cyano-N′-(phenylethyl)-3-pyridinecarboximidamide methanesulfonate), which possesses only KCO activity; and nitroglycerin (NG) were determined on the motility of the ureter, urinary bladder and urethra of rats. Bladder contraction was induced by infusion of fluid into the bladder of conscious rats and recorded on a cystometrogram. KRN2391 and Ki1769 (both 0.3 mg/kg, i.v.) prolonged the micturition interval immediately after the injection, but NG (5 mg/kg, i.v.) did not. Peristaltic movement of the ureter, recorded in anesthetized rats, was inhibited by i.v. injection of KRN2391 and Ki1769 (both 0.03 mg/kg). However, when NG, NaN02, N-nitro L-arginine methylester and methylene blue were applied directly to the ureter, no change in movement of the ureter was detected. KRN2391 (0.03 mg/kg, i.v.) and Ki1769 (0.3 mg/kg, i.v.) reduced the resistance to fluid infusion through the urethral lumen in anesthetized rats, whereas NG (0.5 mg/kg, i.v.) only reduced this resistance transiently. These results indicate that KCO activity had an inhibitory effect on the motility of the ureter, bladder and urethra. On the other hand, nitrate activity had an inhibitory effect on urethral tonus, corresponding to that induced by KCO activity.

Studies of the KATP Channel Opening Activity of the New Dihydropyridine Compound 9-(3-Cyanophenyl)-3,4,6,7,9,10-Hexahydro-1,8-(2H, 5H)-Acridinedione in Bladder Detrusor In Vitro

Studies of the KATP Channel Opening Activity of the New Dihydropyridine Compound 9-(3-Cyanophenyl)-3,4,6,7,9,10-Hexahydro-1,8-(2H, 5H)-Acridinedione in Bladder Detrusor In Vitro

Studies of the KATP Channel Opening Activity of the New Dihydropyridine Compound 9-(3-Cyanophenyl)-3,4,6,7,9,10-Hexahydro-1,8-(2H, 5H)-Acridinedione in Bladder Detrusor In Vitro

The potassium (K+) channel opening activity of ZM244085 (9-(3-cyanophenyl)-3,4,6,7,9,10-hexahydro-1,8-(2H,5H)-acridined ione, CAS 149398-59-4), a novel dihydropyridine (DHP), was ascertained. In a set of functional assays, its mechanoinhibitory effect on myogenic activity of guinea pig bladder detrusor muscles, either mildly or highly depolarized with 15 or 80 mmol/l KCl, was measured. ZM244085 had negligible effect on the tone of the detrusor contracted with 80 mmol/l KCl but reduced the myogenic activity induced with 15 mmol/l KCl (IC50=4.2 +/- 0.4 mumol/l). Glibenclamide, an ATP-sensitive K+ (KATP) channel blocker, competitively antagonized this action of ZM244085 with a pA2 value of 7.6. This functional profile of ZM244085 is similar to that of the prototypic K+ channel opener cromakalim but stands in contrast to that of typical DHP Ca2+ channel blockers such as nifedipine and nimodipine. The membrane potential of the guinea pig detrusor, recorded with intracellular microelectrodes, was hyperpolarized 6.8 +/- 3.1 mV by ZM244085 (10 mumol/l). This hyperpolarization was completely blocked by glibenclamide but not affected by apamin (10 mumol/l), a toxin blocking specifically small conductance and Ca2+ dependent K+ (SKCa) channels. ZM244085 (10 mumol/l) increased the whole cell KATP current in isolated guinea pig detrusor cells by 8.8 +/- 2.5 pA, but failed to activate large conductance and Ca2+ dependent K+ (BKCa) channels in excised inside-out membrane patches from those cells. The results from these studies showed that ZM244085 is a K+ channel opener which activates predominantly KATP channels in vitro to relax bladder detrusors.

Interrelationship of cardiovascular effects, plasma levels of nicorandil, and vascular cGMP formation in conscious rats.

The relationship between the dual activity of nicorandil (KATP channel-opening activity and nitrate-like action), plasma levels, and changes in vascular cGMP levels and cardiovascular parameters was investigated in conscious rats. Nicorandil (3 mg kg(-1), p.o.) was rapidly absorbed and caused a significant reduction in blood pressure, lasting for at least 1 h, increases in heart rate and femoral blood flow, and decreases in femoral vascular resistance. These were entirely abolished by intravenous glibenclamide (20 mg kg(-1)). The plasma concentration of nicorandil reached a maximum 30 min after dosing. After administration of nicorandil, a correlation was observed between blood pressure and plasma nicorandil level or femoral vascular resistance. A significant increase (P < 0.05) in the cGMP content of the thoracic aorta occurred 15 min after administration of nicorandil, and persisted for at least 2 h. These results imply that nicorandil induces vasodilatation by opening KATP channels in peripheral resistance vessels, leading to overt reduction of blood pressure, but acts on conductance vessels mainly through nitrate-like activity.

Synthesis of 2,3,4a,11b-tetrahydro-oxazino[2,3-c]benzopyran-9-carbonitriles as ATP-sensitive potassium channel openers

A series of optically active tetrahydro-oxazino[2,3-c]benzopyran derivatives have been synthesized and evaluated for potassium channel opening activity. (4aR,11bR)-1-Benzoyl- 5,5-dimethyl-2,3,4a,11b-tetrahydro-oxazino[2,3-c]benzopyran-9-carb onitrile ((-)-11e) was identified as a bladder-selective potassium channel opener (IC50, bladder = 8.15 microM, IC50, portal vein = 34.5 microM).

Contribution of calcium-sensitive potassium channels to NS1619-induced relaxation in human pregnant myometrium.

Large-conductance, calcium-sensitive potassium channels (BK(Ca)) are found at high density in the pregnant human myometrium. We have investigated, using isolated myometrial strips and freshly dispersed human myometrial cells, the action of a novel drug (NS1619) which has potassium channel opening activity. Isometric tension experiments demonstrated that NS1619 has a potent, relaxant effect on the pregnant human myometrium. Using both the inside-out and outside-out configurations of the patch-clamp technique, NS1619 appears to act directly on myometrial BK(Ca) channels to stimulate channel activity by increasing the time spent in the open state by this group of potassium channels. Consequently, the myometrial BK(Ca) channel may be a novel target site for drug intervention in clinical conditions, e.g. failure to labour, preterm labour or dysmenorrhoea, which may require either the augmentation or inhibition of uterine K+ channel activity.

ChemInform Abstract: Discovery of a Novel Class of BK Channel Openers: Enantiospecific Synthesis and BK Channel Opening Activity of 3‐(5‐Chloro‐2‐ hydroxyphenyl)‐1,3‐dihydro‐3‐hydroxy‐6‐trifluoromethyl‐2H‐indol‐2‐one.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

DISCOVERY OF A NOVEL CLASS OF BK CHANNEL OPENERS: ENANTIOSPECIFIC SYNTHESIS AND BK CHANNEL OPENING ACTIVITY OF 3-(5-CHLORO-2-HYDROXYPHENYL)-1,3-DIHYDRO-3-HYDROXY-6-(TRIFLUOROMETHYL)-2H-INDOL-2-ONE

Abstract 3-Aryl-3-hydroxyindol-2-ones have been identified as a novel class of BK channel openers. Synthesis of both racemic and chiral 3-aryl-3-hydroxyindolones is described along with their electrophysiological evaluation as activators of the cloned BK channel mSlo expressed in Xenopus laevis oocytes. The preliminary SAR data indicate the importance of both an electron-withdrawing substituent on the oxindole nucleus and the phenolic hydroxyl for expression of BK channel opening properties. Moreover, the dependence of BK channel opening activity on the absolute configuration of the chiral center in this pharmacophore has been demonstrated. © 1997 Elsevier Science Ltd.

Effects of levcromakalim and nucleoside diphosphates on glibenclamide-sensitive K+ channels in pig urethral myocytes.

1. Effects of levcromakalim and nucleoside diphosphates (NDPs) on both membrane currents and unitary currents in pig proximal urethra were investigated by use of patch clamp techniques (conventional whole-cell configuration, nystatin perforated patch, cell-attached configuration and inside-out patches). 2. Levcromakalim produced a concentration-dependent outward current at a holding potential of -50 mV. The peak current amplitude showed little variation when measured by either conventional whole-cell or nystatin perforated patch configurations. 3. In conventional whole-cell configuration, the levcromakalim (100 microM)-induced outward current decayed by about 90% in 18 min. In contrast, with the nystatin perforated patch, approximately 86% of the levcromakalim-induced outward current still remained after 18 min. 4. The peak amplitude of the levcromakalim (100 microM)-induced outward membrane current recorded by the conventional whole-cell configuration was greatly reduced by inclusion of 5 mM EDTA in the pipette. The much smaller but significant outward membrane current remaining was abolished by glibenclamide. 5. In conventional whole-cell recordings, inclusion of an NDP in the pipette solution induced a small outward current which slowly reached a maximal amplitude (in 2 to 10 min) and was suppressed by glibenclamide. Addition of 100 microM levcromakalim after the NDP-induced current had peaked activated a further outward current which was larger than that recorded in the absence of NDPs. Approximately 50% of this current still remained at 18 min, even when conventional whole-cell configuration was used. 6. In the cell-attached mode in symmetrical 140 mM K+ conditions, glibenclamide inhibited the 100 microM levcromakalim-activated 43 pS K+ channel in a concentration-dependent manner, showing an inhibitory dissociation constant (Ki) of approximately 520 nM. 7. In inside-out patches in which the glibenclamide-sensitive K+ channel had run down after exposure to levcromakalim, both uridine 5'-diphosphate (UDP) and MgATP were capable of reactivating the channel. Further application of Mg2+ to the UDP-reactivated K+ channels enhanced the channel activity reversibly. 8. In inside-out patches UDP was capable of activating the glibenclamide-sensitive K+ channel without levcromakalim, providing that there was free Mg2+ present (either UDP in 5 mM EGTA or UDP in 5 mM EDTA with Mg2+). Additional application of levcromakalim caused a further reversible activation of channel opening. 9. In the presence of levcromakalim, application of adenosine 5'-triphosphate (ATP) to the inner surface of the membrane patch inhibited UDP-reactivated channel opening in a concentration-dependent manner. 10. Addition of an untreated cytosolic extract of pig proximal urethra reactivated the glibenclamide-sensitive K+ channel in the presence of 100 microM levcromakalim in inside-out patches. 11. These results demonstrate the presence in the pig proximal urethra of a glibenclamide-sensitive K+ channel that is blocked by intracellular ATP and can be activated by levcromakalim. Intracellular UDP can reactivate the channel after rundown. Additionally, intracellular Mg2+ may play an important role in regulating the channel activity.

The equine periodic paralysis Na+ channel mutation alters molecular transitions between the open and inactivated states.

1. The Na+ channel mutation associated with equine hyperkalaemic periodic paralysis (HPP) affects a highly conserved phenylalanine residue in an unexplored region of the alpha-subunit. This mutation was introduced into the rat skeletal muscle Na+ channel gene at the corresponding location (i.e. F1412L) for functional expression and characterization in Xenopus oocytes. 2. In comparison with wild-type (WT) channels, equine HPP channels showed clear evidence for disruption of inactivation: increased time-to-peak current, slowed rates of whole-cell current decay, significant increases in sustained current, rightward shifts in the steady-state inactivation curve by 9.5 mV, a 6-fold acceleration in the rate of recovery from inactivation at -80 mV, decreased number of blank single-channel sweeps, repetitive opening of single channels throughout depolarizing steps, increased open probability per sweep, and an increased mean open time. 3. The observed disruption of inactivation in HPP occurred without measurable changes in steady-state activation and first latency kinetics of channel opening. 4. Kinetic modelling demonstrates that the equine HPP phenotype can be simulated by altering the rate constants for transitions entering and leaving the inactivated states resulting from an energetic destabilization of the inactivated state. 5. These results suggest that the highly conserved cytoplasmic end of the third transmembrane segment (S3) in the fourth internal repeat domain (domain IV) plays a critical role in Na+ channel inactivation.

Tilisolol hydrochloride dilates coronary arteries through an ATP-sensitive K+-channel opening mechanism in dogs

Tilisolol is a beta-blocking agent with vasodilatory properties that was recently shown to possess a potassium (K+) channel opening activity. We investigated whether tilisolol has vasodilatory effects on coronary circulation in dogs. Mongrel dogs were chronically instrumented for measurements of circumflex coronary artery diameter (CoD) and coronary blood flow (CBF). We compared the effects of tilisolol on dog coronary arteries with those of two beta-blockers, propranolol and arotinolol. Both propranolol (1 mg/kg, intravenously, i.v.) and arotinolol (0.25 mg/kg, i.v.) decreased CoD and increased coronary vascular resistance (CVR). Tilisolol (2 mg/kg, i.v.) decreased CVR but had no significant effect on CoD. To investigate the mechanism of the coronary action of tilisolol, we examined differences in the response to tilisolol in the absence and presence of glibenclamide, an ATP-sensitive K+ channel blocker. Tilisolol (1,2,4, and 8 mg/kg, i.v.) produced a dose-dependent decrease in CVR without glibenclamide, whereas pretreatment with glibenclamide significantly suppressed this effect. Without glibenclamide, tilisolol had no significant effect on CoD at doses of 1-4 mg/kg (i.v.). However, at the higher dose of 8 mg/kg (i.v.), tilisolol significantly increased CoD (1.00 +/- 0.15%, p < 0.01). After pretreatment with glibenclamide, tilisolol (1-8 mg/kg, i.v.) produced a significant decrease in CoD. Therefore, we concluded that tilisolol exerts its vasodilatory effect on the coronary circulation through an ATP-sensitive K+ channel opening mechanism, and that its vasodilatory action is more prominent in coronary resistance vessels than in large coronary arteries.