Behavioral and pharmacological validation of the gerbil forced-swim test: effects of neurokinin-1 receptor antagonists

Several studies have suggested that neurokinin-1 (NK1) receptor antagonists may have therapeutic potential as novel antidepressant drugs. To test these compounds preclinically, gerbils have become one of the preferred species in that they demonstrate close NK1 receptor homology with humans and bind NK1 antagonists with higher affinity than rats and mice. The intent of the present study was to determine whether the forced-swim test (FST), one of the most commonly used animal tests of antidepressant-like activity, could be adapted for use with the gerbil. Critical factors in the establishment of this assay included swim tank diameter, weight, and sex of the animals tested. Pharmacological validation of the FST using standard antidepressant compounds (eg fluoxetine, paroxetine, desipramine) resulted in decreased immobility time during the test, indicative of an antidepressant-like effect. Similar to results reported for the rat and mouse FST, the antipsychotic drug haloperidol increased immobility, whereas the psychostimulant, amphetamine decreased immobility, and anxiolytic drugs (eg buspirone) had no effect. Investigation into the locomotor effects of all compounds tested was consistent with previous reports in other species, with the exception of paroxetine, which produced hyperactivity at therapeutically effective doses in gerbils. In addition to standard antidepressants, NK1 antagonists (L-733060, MK-869, and CP-122721) all reduced immobility in the gerbil FST without affecting locomotor activity. Overall, these results suggest that the gerbil is an ideal species for use in the FST, and that this paradigm may have predictive validity for identifying novel antidepressant compounds.

Conformationally restricted homotryptamines. Part 4: Heterocyclic and naphthyl analogs of a potent selective serotonin reuptake inhibitor

A series of hybrid molecules containing the cyclopropylmethylamino side chain found in homotryptamine (1S,2S)-2c and an isosteric heteroaryl or naphthyl core were prepared and their binding affinities for the human serotonin transporter determined. The most potent isosteres were CN-substituted naphthalenes. These results demonstrate that isosteric aromatic cores which lack an H-bond donor site may be substituted for the indole nucleus without substantial loss in hSERT binding.

Conformationally restricted homotryptamines 3. Indole tetrahydropyridines and cyclohexenylamines as selective serotonin reuptake inhibitors

A series of indole tetrahydropyridine and indole cyclohexenylamines was prepared, and their binding affinities at the human serotonin transporter (SERT) were determined. In particular, a nitrile substituent at the C5 position of the indole ring gave potent SERT activity. The stereochemistry of the N,N-dimethylamine substituent was determined for the most potent indole cyclohexenylamine, 6a. The enantiomers of 6a were energy minimized and compared to other conformationally restricted SSRIs. Compound 6a was found to give a dose-response similar to the SSRI fluoxetine in microdialysis studies in rats.

Chemical genetics reveals an RGS/G-protein role in the action of a compound

We report here on a chemical genetic screen designed to address the mechanism of action of a small molecule. Small molecules that were active in models of urinary incontinence were tested on the nematode Caenorhabditis elegans, and the resulting phenotypes were used as readouts in a genetic screen to identify possible molecular targets. The mutations giving resistance to compound were found to affect members of the RGS protein/G-protein complex. Studies in mammalian systems confirmed that the small molecules inhibit muscarinic G-protein coupled receptor (GPCR) signaling involving G-αq (G-protein alpha subunit). Our studies suggest that the small molecules act at the level of the RGS/G-αq signaling complex, and define new mutations in both RGS and G-αq, including a unique hypo-adapation allele of G-αq. These findings suggest that therapeutics targeted to downstream components of GPCR signaling may be effective for treatment of diseases involving inappropriate receptor activation.

The authors have utilized Caenorhabditis elegans, and yeast genetics, combined with mammalian tissue and cell culture experiments to investigate the mechanism of action of a unique set of small molecules. These molecules are active in tissue models of urinary incontinence and allow for increased bladder filling. In the course of studying sensitivity and resistance to these compounds, Fitzgerald et al. uncovered novel alleles of RGS and Gq proteins. Further characterization of one such allele identified that its action conferred a hypo-adaptive phenotype on yeast during pheromone signaling assays. Their data as a whole indicate that these small molecules are able to diminish signaling from G-protein coupled receptors (GPCR) downstream of the receptors themselves. Since GPCR signaling is very important in many diseases in humans, the novel mechanism of these compounds may offer new ways to treat human disease.

Analogs of a potent maxi-K potassium channel opener with an improved inhibitory profile toward cytochrome P450 isozymes

Quinolinone 1 is a potent maxi-K potassium channel opener. In an effort to design analogs of 1 with a better inhibitory profile toward the CYP2C9 isozyme, the two acidic sites were chemically modified independently to generate a number of analogs. These analogs were evaluated as maxi-K channel openers in vitro using Xenopus laevis oocytes expressing cloned hSlo maxi-K channels. Compounds 15, 17, and 19 showed potent activity as maxi-K channel openers and were further evaluated for inhibition of the activity of the CYP2C9 isozyme. Compounds 17 and 19 showed diminished inhibitory potency against 2C9 and also against a panel of other more common CYP isozymes.

Conformationally restricted homotryptamines. 2. Indole cyclopropylmethylamines as selective serotonin reuptake inhibitors

A series of indole cyclopropylmethylamines were found to be potent serotonin reuptake inhibitors. Nitrile substituents at the 5 and 7 positions of the indole ring gave high affinity for hSERT, and the preferred cyclopropane stereochemistry was determined to be (1S,2S)-trans. The cis-cyclopropanes had 20- to 30-fold less affinity than the trans, and the preferred cis stereochemistry was (1R,2S)-cis. Substitution of the indole N-1 position with methyl or ethyl groups gave a 10- to 30-fold decrease in affinity for hSERT, suggesting either a hydrogen-bonding interaction or limited steric tolerance in the region of the indole nitrogen. Compound (+)-12a demonstrated potent hSERT binding (Ki = 0.18 nM) in vitro and was more than 1000-fold less potent at hDAT, hNET, 5-HT1A, and 5-HT6. In vivo, (+)-12a produced robust, dose-dependent increases in extracellular serotonin in rat frontal cortex typical of a selective serotonin reuptake inhibitor. The maximal response produced by (+)-12a was similar to that of fluoxetine but at an approximately 10-fold lower dose.

The pharmacology of DMP696 and DMP904, non-peptidergic CRF1 receptor antagonists

CRF(1) antagonists DMP696 and DMP904 were designed as drug development candidates for the treatment of anxiety and depression. Both compounds display nanomolar affinity for human CRF(1) receptors, and exhibit >1000-fold selectivity for CRF(1) over CRF(2) receptors and over a broad panel of other proteins. DMP696 and DMP904 block CRF-stimulated adenylyl cyclase activity in cortical homogenates and cell-lines expressing CRF(1) receptors. Both compounds inhibit CRF-stimulated ACTH release from rat pituitary corticotropes. Binding and functional studies indicate that DMP696 and DMP904 behave as noncompetitive full antagonists. DMP696 and DMP904 exhibit anxiolytic-like efficacy in several rat anxiety models. In the defensive withdrawal test, both compounds reduce exit latency with lowest effective doses of 3 and 1 mg/kg, respectively. The anxiolytic-like effect is maintained over 14 days of repeated dosing. In the context of a novel environment used in this test, DMP696 and DMP904 reverse mild stress-induced increases in plasma CORT secretion but at doses 3-4-fold greater than those required for anxiolyticlike efficacy. DMP696 and DMP904 are ineffective in three depression models including the learned helplessness paradigm at doses up to 30 mg/kg. At lowest anxiolytic-like doses, DMP696 and DMP904 occupy >50% CRF(1) receptors in the brain. The in vivo IC(50) values (plasma concentrations required for occupying 50% CRF(1) receptors) estimated based upon free, but not total, plasma concentrations are an excellent correlation with the in vitro IC(50) values. Neither compound produces sedation, ataxia, chlordiazepoxide-like subjective effects or adverse effects on cognition at doses 10-fold higher than anxiolytic-like doses. Neither compound produces physiologically significant changes in cardiovascular, respiratory, gastrointestinal or renal functions at anxiolytic-like doses. DMP696 and DMP904 have favorable pharmacokinetic profiles with good oral bioavailabilities. The overall pharmacological properties suggest that both compounds may be effective anxiolytics with low behavioral side effect liabilities.

Neurochemical, pharmacokinetic, and behavioral effects of the novel selective serotonin reuptake inhibitor BMS-505130

BMS-505130 is a potent and selective serotonin transport inhibitor; K(i) for binding to the serotonin transporter = 0.18 nM (K(i) values for binding to the norepinephrine and dopamine transporters = 4.6 and 2.1 microM, respectively). In platelet serotonin uptake studies BMS-505130 (5 mg/kg, p.o.) produced a robust inhibition of serotonin uptake. In microdialysis studies oral dosing with BMS-505130 produced a dose-dependent increase in cortical serotonin levels that reached a maximal effect of 200% above baseline at a dose of 1 mg/kg, p.o.; the peak serotonin response was transient in nature. Following oral administration, peak plasma concentrations of BMS-505130 reached Tmax at 1.6 +/- 0.7 h and then declined to concentrations <10% of Cmax within the following 6 h; plasma half-life following i.v. dosing was 0.46 +/- 0.02 h. Parallel microdialysis and pharmacokinetic studies revealed that changes in serotonin levels in the cortex mirrored changes in the brain concentration of BMS-505130. In a behavioral assay known to be sensitive to selective serotonin reuptake inhibitors (SSRIs), mouse tail suspension, BMS-505130 produced a robust response after either oral or intraperitoneal dosing. BMS-505130 exhibits a pharmacological, neurochemical and behavioral profile consistent with a potent SSRI. Moreover, BMS-505130's short half-life may be advantageous for the treatment of premature ejaculation where an acute effect to delay ejaculation followed by a relatively rapid fall in SSRI plasma concentrations might be desirable.

4-Aryl-3-(mercapto)quinolin-2-ones: novel maxi-K channel opening relaxants of corporal smooth muscle

A novel series of 4-aryl-3-(mercapto)quinolin-2-one derivatives was prepared and evaluated as openers of the cloned maxi-K channel hSlo expressed in Xenopus laevis oocytes by utilizing electrophysiological methods. The effect of these maxi-K openers on corporal smooth muscle was studied in vitro using isolated rabbit corpus cavernosum. In vivo efficacy has been demonstrated with a selective maxi-K opening relaxant in a rat model of erectile function.

Effect of 4-(5-Chloro-2-hydroxyphenyl)-3-(2-hydroxyethyl)-6-(trifluoromethyl)-quinolin-2(1H)-one (BMS-223131), a Novel Opener of Large Conductance Ca2+-Activated K+ (Maxi-K) Channels on Normal and Stress-Aggravated Colonic Motility and Visceral Nociception

We evaluated the effects of 4-(5-chloro-2-hydroxyphenyl)-3-(2-hydroxyethyl)-6-(trifluoromethyl)-quinolin-2(1H)-one (BMS-223131), an opener of large conductance Ca(2+)-activated potassium (maxi-K) channels, on normal and stress-exacerbated colonic motility and visceral nociception in the rat. Fecal output was employed as an index of motility. Visceral nociception, in response to intracolonic balloon distension (10-90 mm Hg; 30 s duration), was evaluated using one of three indices: change in blood pressure, abdominal withdrawal, or myoelectrical activity. BMS-223131 (2, 6, or 20 mg/kg i.p.) produced a small but dose-dependent and significant reduction in cumulative 24-h fecal output. Fecal output in response to stress (1-h restraint plus bursts of air to the face) was markedly inhibited by BMS-223131, and moisture content was significantly reduced. With regard to visceral pain, the transient and distention-dependent reduction in arterial pressure in anesthetized animals was inhibited by BMS-223131 in a dose-dependent manner. Distension-induced abdominal withdrawal in conscious rats was also dose-dependently attenuated by BMS-223131. BMS-223131 at a dose of 20 mg/kg markedly attenuated the increase in myoelectrical activity evoked by balloon distention in conscious animals. BMS-223131 was also evaluated in viscerally hypersensitive rats (sensitized as neonates by intracolonic mustard oil) where it produced a robust dose-dependent attenuation of the abdominal withdrawal response. Compared with naive animals, BMS-223131 was more potent in the sensitized animals. Thus, BMS-223131 effectively reduced stress-induced colonic motility and visceral nociception supporting the potential utility of maxi-K channel openers for the treatment of bowel disorders involving dysfunctional motility and visceral sensitivity.

BL-1249 [(5,6,7,8-tetrahydro-naphthalen-1-yl)-[2-(1H-tetrazol-5-yl)-phenyl]-amine]: a putative potassium channel opener with bladder-relaxant properties

BL-1249 [(5,6,7,8-tetrahydro-naphthalen-1-yl)-[2-(1H-tetrazol-5-yl)-phenyl]-amine] produced a concentration-dependent membrane hyperpolarization of cultured human bladder myocytes, assessed as either a reduction in fluorescence of the voltage-sensitive dye bis-(1,2-dibutylbarbituric acid)trimethine oxonol (EC50 = 1.26 +/- 0.6 microM) or by direct electrophysiological measurement (EC50 = 1.49 +/- 0.08 microM). BL-1249 also produced a membrane hyperpolarization of acutely dissociated rat bladder myocytes. Voltage-clamp studies in human bladder cells revealed that BL-1249 activated an instantaneous, noninactivating current that reversed near E(K). The BL-1249-evoked outward K+ current was insensitive to blockade by glyburide, tetraethylammonium, iberiotoxin, 4-aminopyridine, apamin, or Mg2+. However, the current was inhibited by extracellular Ba2+ (10 mM). In in vitro organ bath experiments, BL-1249 produced a concentration-dependent relaxation of 30 mM KCl-induced contractions in rat bladder strips (EC50 = 1.12 +/- 0.37 microM), yet had no effect on aortic strips up to the highest concentration tested (10 microM). The bladder relaxation produced by BL-1249 was partially blocked by Ba2+ (1 and 10 mM) but not by apamin, iberiotoxin, 4-aminopyridine, glyburide, or tetraethylammonium. In an anesthetized rat model, BL-1249 (1 mg/kg i.v.) decreased the number of isovolumic contractions, without significantly affecting blood pressure. Thus, BL-1249 behaves as a potassium channel activator that exhibits bladder versus vascular selectivity both in vitro and in vivo. A survey of potassium channels exhibiting sensitivity to extracellular Ba2+ at millimolar concentration revealed that the expression of the K2P2.1 (TREK-1) channel was relatively high in human bladder cells versus human aortic cells, suggesting this channel as a possible candidate target for BL-1249.

1-(2-pyrimidinyl)-piperazine, a buspirone metabolite, modulates bladder function in the anesthetized rat

AIMS

To examine the effects of 1-(2-pyrimidinyl)-piperazine (1-PP), a buspirone metabolite, on bladder function in vivo.

METHODS

Micturition reflexes in the rat were evaluated in two models of bladder function; a constant infusion model employing 0.5% acetic acid and an isovolumic model.

RESULTS

In the constant infusion model, 1-PP (0.14-1.32 mg/kg) dose-dependently and significantly decreased the number of bladder contractions measured during a 30 min recording period, with little effect on the pressure developed during each contraction. 1-PP is an alpha2-adrenergic receptor antagonist. The alpha2 antagonists BRL44408 (alpha2A vs. alpha2B selective; 0.3 and 1 mg/kg), imiloxan (alpha(2B) vs. alpha2A selective; 1 mg/kg), and yohimbine (non-subtype selective; 1 mg/kg; but not 0.3 mg/kg) also significantly reduced the number of contractions. Vehicle was without effect. In the isovolumic model, 1-PP (0.03-1.0 mg/kg) produced a dose-dependent and significant reduction in the number of bladder contractions recorded during a 15 min assessment period, with the maximum effect observed at 0.3 mg/kg. 1-PP had little effect on blood pressure; the only effect was observed at the highest dose (1 mg/kg) where it produced a transient 17% decrease in pressure. Cromakalim and tolterodine served as comparitors in all studies.

CONCLUSIONS

1-PP decreased the number of bladder contractions evoked by the micturition reflex at doses that had little effect on either the pressure developed during each bladd er contraction or on blood pressure. The effects of 1-PP are likely mediated primarily by alpha2 receptor antagonism.

Design, synthesis, and biological evaluation of 1,2,3,7-tetrahydro-6h-purin-6-one and 3,7-dihydro-1h-purine-2,6-dione derivatives as corticotropin-releasing factor(1) receptor antagonists

A growing body of evidence suggests that CRF(1) receptor antagonism offers considerable therapeutic potential in the treatment of diseases resulting from elevated levels of CRF, such as anxiety and depression. A series of novel 1,2,3,7-tetrahydro-6H-purin-6-one and 3,7-dihydro-1H-purine-2,6-dione derivatives was synthesized and evaluated as corticotropin releasing factor-1 (CRF(1)) receptor antagonists. Compounds within this series, represented by compound 12d (IC(50) = 5.4 nM), were found to be highly potent CRF(1) receptor antagonists. In addition, compounds 12d and 12j were determined to be selective CRF(1) antagonists. The synthesis, structure-activity relationships and pharmacokinetic properties of compounds within this series is presented.

Effect of the 5HT1A receptor partial agonist buspirone on colorectal distension-induced pseudoaffective and behavioral responses in the female Wistar rat

In the present study, we have evaluated the visceral analgesic property of buspirone, a 5HT(1A) receptor partial agonist, on colorectal distension-induced mean arterial pressure and behavioral changes in anesthetized and awake Wistar rats, respectively. The selection of the rat strain was based on the observation that anesthetized Wistar rats exhibited a more prominent mean arterial pressure change in response to colorectal distention when compared to other strains (Sprague-Dawley, Wistar-Kyoto and Spontaneously Hypertensive). Buspirone dose-dependently (0.1-1 mg/kg, i.v.) antagonized mean arterial pressure change over a range of distensions (10-90 mmHg). In parallel studies conducted in awake animals, buspirone (1-5 mg/kg, s.c.) attenuated the abdominal withdrawal response, a nociceptive behavior, in response to colorectal distension. This effect was antagonized by co-administration of the 5-HT(1A) receptor antagonist N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl]-N-2- pyridinylcyclohexanecarboxamide (WAY-100635) (5 mg/kg, s.c.). We conclude that buspirone exhibits significant visceral analgesic property in two models of abdominal nociception.

Tetrahydronaphthalene-derived amino alcohols and amino ketones as potent and selective inhibitors of the delayed rectifier potassium current IKs

Class III anti-arrhythmic drugs (e.g., dofetilide) prolong cardiac action potential duration (APD) by blocking the fast component of the delayed rectifier potassium current (I(Kr)). The block of I(Kr) can result in life threatening ventricular arrhythmias (i.e., torsades de pointes). Unlike I(Kr), the role of the slow component of the delayed rectifier potassium current (I(Ks)) becomes significant only at faster heart rate. Therefore selective blockers of I(Ks) could prolong APD with a reduced propensity to cause pro-arrhythmic side effects. This report describes structure-activity relationships (SARs) of a series of I(Ks) inhibitors derived from 6-alkoxytetralones with good in vitro activity (IC(50) > or =30 nM) and up to 40-fold I(Ks)/I(Kr) selectivity.

4-Aryl-3-(hydroxyalkyl)quinolin-2-ones: novel maxi-K channel opening relaxants of corporal smooth muscle targeted for erectile dysfunction

Novel 4-aryl-3-(hydroxyalkyl)quinoline-2-one derivatives were prepared and evaluated as openers of the cloned maxi-K channel hSlo expressed in Xenopus laevis oocytes by utilizing electrophysiological methods. The effect of these maxi-K openers on corporal smooth muscle was studied in vitro using isolated rabbit corpus cavernosum. From this study, a potent maxi-K opener was identified as an effective relaxant of rabbit corporal smooth muscle and shown to be active in an in vivo animal model of male erectile function.

Partially purified Grammostola spatulata venom inhibits stretch activated calcium signaling in bladder myocytes and improves bladder compliance in an in vitro rat whole bladder model

PURPOSE

Stretch activated nonselective cationic channels (SACs) are present in urinary bladder myocytes and thought to be activated during bladder filling. We investigated the relationship of stretch induced calcium signaling inhibition in bladder myocytes and bladder compliance modulation in an in vitro whole bladder model.

MATERIALS AND METHODS

Grammostola spatulata venom (SpiderPharm, Yarnell, Arizona) was purified by preparative high performance liquid chromatography. The resulting fractions were examined for their ability to inhibit the swelling activated intracellular free Ca2+ signal in cultured bladder myocytes. An in vitro rat whole bladder model was used to examine the effect of venom fractions on compliance, emptying and spontaneous contractions during bladder filling.

RESULTS

The gadolinium ion, a SAC inhibitor, and venom fractions caused concentration dependent inhibition of the swelling activated intracellular free Ca2+ signal in bladder myocytes. When tested in a rat isolated whole bladder model, 0.1 and 0.2 mg./ml. partially purified venom produced a significant improvement in compliance (p <0.05), caused significant inhibition of the frequency of spontaneous bladder contractions (mean +/- SEM 35.8% +/- 3.7% and 62.3% +/- 4.4%, respectively, p </=0.001) and significantly reduced spontaneous bladder emptying, that is emptying in the absence of exogenous stimulation (38.8% +/- 5.6% and 43.9% +/- 2.5%, respectively, p </=0.0008). However, it produced little or no inhibition of carbachol induced bladder emptying.

CONCLUSIONS

Our data suggest that the activation of stretch induced signaling in bladder myocytes may have an important role in myogenic regulation of bladder contractility during bladder filling. Inhibition of SACs may improve bladder compliance.

Design and synthesis of 4-substituted benzamides as potent, selective, and orally bioavailable I(Ks) blockers

Multiple delayed rectifier potassium currents, including I(Ks), are responsible for the repolarization and termination of the cardiac action potential, and blockers of these currents may be useful as antiarrhythmic agents. Modification of compound 5 produced 19(S) that is the most potent I(Ks) blocker reported to date with >5000-fold selectivity over other cardiac ion channels. Further modification produced 24A with 23% oral bioavailability.

Pharmacologic characterization of BMS-191095, a mitochondrial K(ATP) opener with no peripheral vasodilator or cardiac action potential shortening activity

Previous work described ATP-sensitive K(+) channel (K(ATP)) openers (e.g., BMS-180448), which retain the cardioprotective activity of agents such as cromakalim while being significantly less potent as vasodilators. In this study, we describe the pharmacologic profile of BMS-191095, which is devoid of peripheral vasodilating activity while retaining glyburide-reversible cardioprotective activity. In isolated rat hearts subjected to 25 min of global ischemia and 30 min of reperfusion, BMS-191095 increased the time to onset of ischemic contracture with an EC(25) of 1.5 microM, which is comparable to 4.7 microM and 3.0 microM for cromakalim and BMS-180448, respectively. Comparisons of cardioprotective and vasorelaxant potencies in vitro and in vivo showed BMS-191095 to be significantly more selective for cardioprotection with virtually no effect on peripheral smooth muscle, whereas cromakalim showed little selectivity. In addition to increasing the time to the onset of contracture, BMS-191095 improved postischemic recovery of function and reduced lactate dehydrogenase release in the isolated rat hearts. The cardioprotective effects of BMS-191095 were abolished by glyburide and sodium 5-hydroxydecanoate (5-HD). BMS-191095 did not shorten action potential duration in normal or hypoxic myocardium within its cardioprotective concentration range nor did it activate sarcolemmal K(ATP) current (< or =30 microM). BMS-191095 opened cardiac mitochondrial K(ATP) with a K(1/2) of 83 nM, and this was abolished by glyburide and 5-HD. These results show that the cardioprotective effects of BMS-191095 are dissociated from peripheral vasodilator and cardiac sarcolemmal K(ATP) activation. Agents like BMS-191095 may owe their cardioprotective selectivity to selective mitochondrial K(ATP) activation.

Identification of [3H]P1075 binding sites and P1075-activated K+ currents in ovine choroid plexus cells

This study examined the pharmacological characteristics of binding sites for the potent K+ channel opener [3H]P1075, as well as the functional effects of P1075 on ionic currents and membrane potential, in ovine choroid plexus (OCP) cells. [3H]P1075 bound to OCP cells with a Kd of 26 +/- 4 nM and a Bmax of 10400 +/- 480 sites/cell. Labelled sites were stereoselective and inhibited by potassium channel openers with a rank order of potency: P1075 > BMS-182264, ((4-[[9cyanoimino)[(1,2,2-trimethylpropyl)amino]-methyl]amino]benz onitrile) > pinacidil >> nicorandil > diazoxide. The K(ATP) channel antagonist glyburide inhibited [3H]P1075 binding with a Ki of 2 microM. The presence of K(ATP) channels on OCP cells was examined by patch clamp and fluorescent (membrane-potential sensitive dye) techniques. In some cells, P1075 activated an outward potassium current which was blocked by glyburide. P1075 produced a glyburide-sensitive, concentration-dependent, hyperpolarization of OCP cells. Levcromakalim hyperpolarized more strongly than its 3R,4S enantiomer, BRL 38226 ((3R-trans)-3,4-dihydro-3-hydroxy-2,2-dimethyl-4-(2-oxo-1-pyrrolidinyl)- 2H-1-benzopyran-6-carbonitrile) indicating a stereoselective interaction. These data indicate that epithelial OCP cells contain glyburide-sensitive K(ATP) channels.

Cardioprotective effect of diazoxide and its interaction with mitochondrial ATP-sensitive K+ channels. Possible mechanism of cardioprotection

Previous studies showed a poor correlation between sarcolemmal K+ currents and cardioprotection for ATP-sensitive K+ channel (KATP) openers. Diazoxide is a weak cardiac sarcolemmal KATP opener, but it is a potent opener of mitochondrial KATP, making it a useful tool for determining the importance of this mitochondrial site. In reconstituted bovine heart KATP, diazoxide opened mitochondrial KATP with a K1/2 of 0.8 mumol/L while being 1000-fold less potent at opening sarcolemmal KATP. To compare cardioprotective potency, diazoxide or cromakalim was given to isolated rat hearts subjected to 25 minutes of global ischemia and 30 minutes of reperfusion. Diazoxide and cromakalim increased the time to onset of contracture with a similar potency (EC25, 11.0 and 8.8 mumol/L, respectively) and improved postischemic functional recovery in a glibenclamide (glyburide)-reversible manner. In addition, sodium 5-hydroxydecanoic acid completely abolished the protective effect of diazoxide. While-myocyte studies showed that diazoxide was significantly less potent than cromakalim in increasing sarcolemmal K+ currents. Diazoxide shortened ischemic action potential duration significantly less than cromakalim at equicardioprotective concentrations. We also determined the effects of cromakalim and diazoxide on reconstituted rat mitochondrial cardiac KATP activity. Cromakalim and diazoxide were both potent activators of K+ flux in this preparation (K1/2 values, 1.1 +/- 0.1 and 0.49 +/- 0.05 mumol/L, respectively). Both glibenclamide and sodium 5-hydroxydecanoic acid inhibited K+ flux through the diazoxide-opened mitochondrial KATP. The profile of activity of diazoxide (and perhaps KATP openers in general) suggests that they protect ischemic hearts in a manner that is consistent with an interaction with mitochondrial KATP.

Alterations in Ito1, IKr and Ik1 density in the BIO TO-2 strain of syrian myopathic hamsters

The BIO TO-2 strain of cardiomyopathic hamster provides a model of dilated low output heart failure. The goal of the study was to determine whether changes in potassium currents occur in this model of heart failure. The densities of Ito1, IKr and IK1 in 8-month-old myopathic hamsters were not significantly different from their age-matched controls. The half-maximum activation voltage (V1/2) of IKr and Ito1, as well as the voltage-dependence of Ito1 inactivation were also similar in both groups at 8 months. Ito1 inactivation exhibited a double exponential time-course; the slow component (tau2), but not the rapid component (tau1), was larger in the myopathic animals. The densities of Ito1, IKr and IK1 were not significantly different in the 8- and 10-month-old control animals. However, the densities of Ito1, IKr and IK1 were all significantly lower in the 10-month-old myopathic hamsters relative to the 10-month-old controls. The V1/2 for IKr and Ito1 activation was the same in myopathic and control animals. tau2, but not tau1, of Ito1 inactivation was again larger in the myopathic animals. The voltage-dependence of Ito1 inactivation was shifted slightly, but significantly, positive in the myopathic animals. Lastly, a sustained outwardly rectifying current that activated upon depolarization was found to be larger in the myopathic animals at both 8 and 10 months of age. In conclusion, many of the alterations in potassium current densities in the 10-month-old cardiomyopathic hamsters are qualitatively similar to the changes observed in the failing human heart.

The novel cardioprotective agent BMS-180448 activates a potassium conductance in cardiac and vascular smooth muscle

The goal of the present study was to further characterize the effects of the novel cardioprotective agent BMS-180448 on potassium fluxes in cardiac and vascular smooth muscle. Exposure of voltage-clamped guinea pig ventricular myocytes to BMS-180448 (300 microM) produced an inhibition of IK followed by the delayed (5.5 +/- 0.5 min) activation of a large time-independent potassium current. At 100 microM, BMS-180448 produced only inhibition of IK. The BMS-180448 activated current was refractory to block by 30 microM glyburide but was largely inhibited by 100 microM alinidine (84 +/- 6% inhibition at +40 mV). Cromakalim (100 microM)-activated currents were fully inhibited by 3 microM glyburide and 79 +/- 4% blocked by 100 microM alinidine. The current responses to BMS-180448 were unaffected by the inclusion of 10 mM UDP (100 microM ATP) in the pipette. BMS-180448 also produced a concentration-dependent increase in 86Rb efflux from aortic strips; efflux responses were increased in low calcium medium and fully antagonized by 3 microM glyburide. Thus, BMS-180448 activates a potassium conductance in both cardiac and smooth muscle. The glyburide sensitivity of the BMS-180448-induced increase in 86Rb efflux from the aortic preparations suggests that this drug activates IKATP in vascular smooth muscle. Moreover, the observation that BMS-180448 (100 microM) partially inhibits the effects of cromakalim in ventricular muscle cells suggests that these drugs interact, directly or indirectly, with a common site in cardiac muscle.

Pharmacological characterization of the isolated canine prostate

PURPOSE

The goal of the present study was to characterize the responses of the isolated normal canine prostate to various contracting and relaxing stimuli to determine which pharmacological agents may have utility against the dynamic component of benign prostatic hyperplasia (BPH).

MATERIALS AND METHODS

Isometric force development was measured in isolated strips of prostate tissue.

RESULTS

The alpha-adrenergic agonists were the most efficacious stimulants tested (phenylephrine EC50=2.1 microM.). Endothelin-1, acting primarily via ETA receptors, was more potent (EC50=27nM.) but less efficacious. Histamine (EC50=14.7 microM.), serotonin (EC50=0.12 microM.), carbachol (EC50=5.9 microM.) and KC1 (EC50=48.8 mM.) were also less efficacious than phenylephrine. Nifedipine was a potent (IC50=28 nM.) and efficacious (74% inhibition) inhibitor of phenylephrine-induced force. Potassium channel activator drugs were also efficacious relaxants, producing approximately 80% inhibition of force; rank order of potency was P1075 > cromakalim > diazoxide. Sodium nitroprusside was a weak relaxant, producing only approximately 40% relaxation at a concentration of 100 micronM. Both isoproterenol and forskolin were effective relaxants (75 to 90% relaxation).

CONCLUSIONS

We conclude that potassium channel activators, adenylate cyclase stimulators, or endothelin antagonists may have utility against the dynamic component of outflow obstruction secondary to BPH.