Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Comorbidities: Linked by Vascular Pathomechanisms and Vasoactive Mediators?

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is often associated with various other syndromes or conditions including mast cell activation (MCA), dysmenorrhea and endometriosis, postural tachycardia (POTS) and small fiber neuropathy (SFN). The causes of these syndromes and the reason for their frequent association are not yet fully understood. We previously published a comprehensive hypothesis of the ME/CFS pathophysiology that explains the majority of symptoms, findings and chronicity of the disease. We wondered whether some of the identified key pathomechanisms in ME/CFS are also operative in MCA, endometriosis and dysmenorrhea, POTS, decreased cerebral blood flow and SFN, and possibly may provide clues on their causes and frequent co-occurrence. Our analysis indeed provides strong arguments in favor of this assumption, and we conclude that the main pathomechanisms responsible for this association are excessive generation and spillover into the systemic circulation of inflammatory and vasoactive tissue mediators, dysfunctional β2AdR, and the mutual triggering of symptomatology and disease initiation. Overall, vascular dysfunction appears to be a strong common denominator in these linkages.

Orthostatic Intolerance after COVID-19 Infection: Is Disturbed Microcirculation of the Vasa Vasorum of Capacitance Vessels the Primary Defect?

Following COVID-19 infection, a substantial proportion of patients suffer from persistent symptoms known as Long COVID. Among the main symptoms are fatigue, cognitive dysfunction, muscle weakness and orthostatic intolerance (OI). These symptoms also occur in myalgic encephalomyelitis/chronic fatigue (ME/CFS). OI is highly prevalent in ME/CFS and develops early during or after acute COVID-19 infection. The causes for OI are unknown and autonomic dysfunction is hypothetically assumed to be the primary cause, presumably as a consequence of neuroinflammation. Here, we propose an alternative, primary vascular mechanism as the underlying cause of OI in Long COVID. We assume that the capacitance vessel system, which plays a key role in physiologic orthostatic regulation, becomes dysfunctional due to a disturbance of the microvessels and the vasa vasorum, which supply large parts of the wall of those large vessels. We assume that the known microcirculatory disturbance found after COVID-19 infection, resulting from endothelial dysfunction, microthrombus formation and rheological disturbances of blood cells (altered deformability), also affects the vasa vasorum to impair the function of the capacitance vessels. In an attempt to compensate for the vascular deficit, sympathetic activity overshoots to further worsen OI, resulting in a vicious circle that maintains OI. The resulting orthostatic stress, in turn, plays a key role in autonomic dysfunction and the pathophysiology of ME/CFS.

An attempt to explain the neurological symptoms of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

There is accumulating evidence of endothelial dysfunction, muscle and cerebral hypoperfusion in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). In this paper we deduce the pathomechanisms resulting in central nervous pathology and the myriad of neurocognitive symptoms. We outline tentative mechanisms of impaired cerebral blood flow, increase in intracranial pressure and central adrenergic hyperactivity and how they can well explain the key symptoms of cognitive impairment, brain fog, headache, hypersensitivity, sleep disturbances and dysautonomia.

Pathophysiology of skeletal muscle disturbances in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Chronic Fatigue Syndrome or Myalgic Encephaloymelitis (ME/CFS) is a frequent debilitating disease with an enigmatic etiology. The finding of autoantibodies against ß2-adrenergic receptors (ß2AdR) prompted us to hypothesize that ß2AdR dysfunction is of critical importance in the pathophysiology of ME/CFS. Our hypothesis published previously considers ME/CFS as a disease caused by a dysfunctional autonomic nervous system (ANS) system: sympathetic overactivity in the presence of vascular dysregulation by ß2AdR dysfunction causes predominance of vasoconstrictor influences in brain and skeletal muscles, which in the latter is opposed by the metabolically stimulated release of endogenous vasodilators (functional sympatholysis). An enigmatic bioenergetic disturbance in skeletal muscle strongly contributes to this release. Excessive generation of these vasodilators with algesic properties and spillover into the systemic circulation could explain hypovolemia, suppression of renin (paradoxon) and the enigmatic symptoms. In this hypothesis paper the mechanisms underlying the energetic disturbance in muscles will be explained and merged with the first hypothesis. The key information is that ß2AdR also stimulates the Na+/K+-ATPase in skeletal muscles. Appropriate muscular perfusion as well as function of the Na+/K+-ATPase determine muscle fatigability. We presume that dysfunction of the ß2AdR also leads to an insufficient stimulation of the Na+/K+-ATPase causing sodium overload which reverses the transport direction of the sodium-calcium exchanger (NCX) to import calcium instead of exporting it as is also known from the ischemia-reperfusion paradigm. The ensuing calcium overload affects the mitochondria, cytoplasmatic metabolism and the endothelium which further worsens the energetic situation (vicious circle) to explain postexertional malaise, exercise intolerance and chronification. Reduced Na+/K+-ATPase activity is not the only cause for cellular sodium loading. In poor energetic situations increased proton production raises intracellular sodium via sodium-proton-exchanger subtype-1 (NHE1), the most important proton-extruder in skeletal muscle. Finally, sodium overload is due to diminished sodium outward transport and enhanced cellular sodium loading. As soon as this disturbance would have occurred in a severe manner the threshold for re-induction would be strongly lowered, mainly due to an upregulated NHE1, so that it could repeat at low levels of exercise, even by activities of everyday life, re-inducing mitochondrial, metabolic and vascular dysfunction to perpetuate the disease.

Effect of obstructive respiratory events on blood pressure and renal perfusion in a pig model for sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with hypertension and the progression of chronic kidney disease (CKD). Renal sympathetic innervation contributes to either condition.

METHODS

We investigated the effect of renal sympathetic denervation (RDN) on blood pressure (BP), renal perfusion, and neurohumoral responses during and after repetitive obstructive apneas in a pig model for OSA. BP, femoral artery, and renal artery flow were measured in 29 spontaneously breathing urethane-chloralose-anesthetized pigs. The effect of RDN (n = 14) and irbesartan (n = 3) was investigated. Repetitive tracheal occlusions for 2 minutes with applied negative tracheal pressure at -80 mbar were performed over 4 hours.

RESULTS

Spontaneous breathing attempts during tracheal occlusion caused an intra-apneic breathing synchronous oscillating pattern of renal flow. Renal flow oscillations were > 2-fold higher compared with femoral flow that almost showed changes proportional to the BP alterations (2.9%/mm Hg vs. 1.3%/mm Hg; P < 0.0001). A marked postapneic BP rise from 102 ± 3 to 172 ± 8 mm Hg (P < 0.00001) was associated with renal hypoperfusion (from 190 ± 24 to 70 ± 20 ml/min; P < 0.00001) occurring after application of obstructive respiratory events. RDN, but not irbesartan, inhibited postapneic BP rises and renal hypoperfusion and attenuated increased plasma renin activity and aldosterone concentration induced by repetitive tracheal occlusions. Additionally, increased urinary protein/creatinine ratio was significantly reduced by RDN, whereas intra-apneic hemodynamic changes or blood gases were not modified by RDN.

CONCLUSIONS

Repetitive obstructive respiratory events result in postapneic BP rises and renal hypoperfusion, as well as neurohumoral responses and increased protein/creatinine ratio. These changes are mainly sympathetically driven because they could be attenuated by RDN.

Sensitization of upper airway mechanoreceptors as a new pharmacologic principle to treat obstructive sleep apnea: investigations with AVE0118 in anesthetized pigs

STUDY OBJECTIVES

Drug treatment for obstructive sleep apnea (OSA) is desirable because at least 30% of patients do not tolerate continuous positive airway pressure (CPAP) treatment. The negative pressure reflex (NPR) involving superficially located mechanoreceptors in the upper airway (UA) is an important mechanism for UA patency inhibitable by topical UA anesthesia (lidocaine). The NPR may serve as a target for pharmacological intervention for a topical treatment of OSA. The objective was to determine the effect of pharmacological augmentation of the NPR on UA collapsibility.

DESIGN

We developed a model of UA collapsibility in which application of negative pressures caused UA collapses in spontaneously breathing α-chloralose-urethane anesthetized pigs as indicated by characteristic tracheal pressure and air flow changes.

SETTING

N/A.

PATIENTS OR PARTICIPANTS

N/A.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

The potassium channel blocker AVE0118 administered topically to the UA in doses of 1, 3, and 10 mg per nostril sensitized the NPR, shifting the mechanoreceptor response threshold for the genioglossus muscle to more positive pressures (P < 0.001; n = 6 per group) and dose-dependently inhibited UA collapsibility. Ten mg of AVE0118 prevented UA collapses against negative pressures of -150 mbar (P < 0.01) for > 4 h in all pigs, while in control pigs the UA collapsed at -50 mbar or less negative pressures. The effect of AVE0118 was abolished by UA lidocaine anesthesia. Acute intravenous administration of naloxone or acetazolamide was ineffective; paroxetine and mirtazepine were weakly effective and fluoxetine was moderately effective in line with reported clinical efficacy.

CONCLUSION

Topical administration of AVE0118 to the UA is a promising pharmacologic approach for the treatment of OSA.

In vitro and in vivo effects of the atrial selective antiarrhythmic compound AVE1231

The novel compound AVE1231 was investigated in order to elucidate its potential against atrial fibrillation. In CHO cells, the current generated by hKv1.5 or hKv4.3 + KChIP2.2b channels was blocked with IC50 values of 3.6 microM and 5.9 microM, respectively. In pig left atrial myocytes, a voltage-dependent outward current was blocked with an IC50 of 1.1 microM, mainly by accelerating the time constant of decay. Carbachol-activated IKACh was blocked by AVE1231 with an IC50 of 8.4 microM. Other ionic currents, like the IKr, IKs, IKATP, ICa, and INa were only mildly affected by 10 microM AVE1231. In guinea pig papillary muscle the APD90 and the upstroke velocity were not significantly altered by 30 microM AVE1231. In anesthetized pigs, oral doses of 0.3, 1, and 3 mg/kg AVE1231 caused a dose-dependent increase in left atrial refractoriness (LAERP), associated by inhibition of left atrial vulnerability to arrhythmia. There were no effects on the ECG intervals, ventricular monophasic action potentials, or ventricular refractory periods at 3 mg/kg AVE1231 applied intravenously. In conscious goats, both AVE1231 (3 mg/kg/h iv) and dofetilide (10 microg/kg/h iv) significantly prolonged LAERP. After 72 hours of tachypacing, when LAERP was shortened significantly (electrical remodelling), the prolongation of LAERP induced by AVE1231 was even more pronounced than in sinus rhythm. In contrast, the effect of dofetilide was strongly decreased. The present data demonstrate that AVE1231 blocks early atrial K channels and prolongs atrial refractoriness with no effects on ECG intervals and ventricular repolarisation, suggesting that it is suited for the prevention of atrial fibrillation in patients.

Effect of the cardioselective, sarcolemmal K(ATP) channel blocker HMR 1098 on atrial electrical remodeling during pacing-induced atrial fibrillation in dogs

PURPOSE

The progressive shortening of the atrial effective refractory period (ERP) during atrial fibrillation (AF) might be due to the activation of the KATP channels by rapid atrial rates. We tested the hypothesis that the cardioselective, sarcolemmal KATP channel blocker HMR 1098 would prevent atrial ERP shortening during AF.

METHODS AND RESULTS

Nine dogs were treated with HMR 1098 (3 mg/kg bolus injection followed by a continuous intravenous (i.v.) infusion at 17 microg/kg/min rate maintained throughout the study) and 7 dogs served as controls receiving i.v. saline. Pharmacological autonomic blockade was induced by i.v. administration of atropine (0.04 mg/kg) and propranolol (0.2 mg/kg) and maintained throughout the study by continuous i.v. infusion of atropine (0.007 mg/kg/h) and propranolol (0.04 mg/kg/h). Rapid right atrial pacing at 50 msec cycle length (CL) was initiated and maintained for 6 hours. High right atrial ERP (HRA-ERP) and corrected sinus node recovery time (HRA-cSNRT), coronary sinus ERP (CS-ERP) and corrected SNRT (CS-cSNRT) at three (400, 300, 200 msec) CLs were measured before and after pacing at different time points. Baseline values were not different between control and treated dogs. In the control group the HRA-ERP progressively shortened (from 179 +/- 21 msec at baseline to 161 +/- 23 msec at 360 min at 400 msec CL) ( p = 0.002), with a gradual decrease, loss or inversion of ERP rate adaptation at shorter (300, 200 msec) CLs. HMR 1098 treatment did not prevent the shortening of HRA-ERP during the first 2 to 3 hours of rapid atrial pacing. However, beginning at 180-240 min, HMR 1098 increased the HRA-ERP ( p = 0.01) to baseline by 360 min. HMR 1098 treatment did not prevent another feature of atrial electrical remodeling, the flattening or inversion of ERP rate adaptation. In neither group did CS-ERP shortening occur. The maximum cSNRT at 360 min prolonged significantly in both groups during HRA and CS pacing as well compared with baseline.

CONCLUSIONS

HMR 1098 treatment did not prevent the shortening of HRA-ERP, the salient feature of atrial electrical remodeling in the first 2 to 3 hours of rapid atrial rates, but did prevent it thereafter. Another characteristic feature of atrial electrical remodeling, the flattening or inversion of physiological ERP rate adaptation was not prevented by HMR 1098 treatment. Sinus node depression was detectable after short-term (6 hours) rapid atrial pacing and was not affected by HMR 1098.

Atrial-selective antiarrhythmic actions of novel Ikur vs. Ikr, Iks, and IKAch class Ic drugs and beta blockers in pigs

BACKGROUND

The Kv1.5 channel, underlying IKur, is supposed to be atrial selective in pigs and humans. We investigated the effects of different potassium channel blockers, i.e. the IKur blockers AVE 0118, S9947 and S20951, with amiodarone (AM), dofetilide (DO), azimilide (AZ), ibutilide (IB), the IKs blocker HMR 1556, atropine (ATR), flecainide (FL), propafenone (PR), d,l-sotalol (SO), atenolol (ATE), and esmolol (ES), on the left and right atrial and ventricular refractoriness and left atrial vulnerability (LAV) in vivo in pigs.

MATERIAL/METHODS

In pentobarbital-anesthetized pigs (n=81), atrial and ventricular effective refractory periods (ERPs) were measured with the S1-S2-extrastimulus-method and QTc time from electrocardiograms. LAV was assessed after S2-extrastimulus to the left atrium.

RESULTS

All IKur blockers prolonged left stronger than right atrial ERP and did not change QTc. All IKr blockers predominantly prolonged the right vs. left atria. AM prolonged both atria equally, and ATR the left only. Pure beta blockers acted predominantly on the left atrium, as did FL and PR, while d,l-sotalol acted predominantly on the right. AVE 0118, S9947, S20951, ibutilide, and d,l-sotalol significantly decreased LAV (-100%, -100%, -82%, -53%, -42%; p<0.05), in contrast to all other drugs.

CONCLUSIONS

The IKur blockers exhibited stronger effects on the left atrium, which itself has shorter refractoriness, but strikingly with no effect on ventricular repolarization, while IKr blockers, IKs blockers, and d,l-sotalol exerted predominantly right atrial effects and known ventricular effects. IKur blockers inhibited atrial tachyarrhythmias stronger than all available drugs. Therefore, IKur blockers seem to be promising new atrial-selective antiarrhythmic drugs.

Atrial effects of the novel K(+)-channel-blocker AVE0118 in anesthetized pigs

OBJECTIVES

AVE0118 is a novel blocker of the K(+) channels K(v)1.5 and K(v)4.3 which are the molecular basis for the human cardiac ultrarapid delayed rectifier potassium current (I(Kur)) and the transient outward current (I(to)). The objective of this study was to investigate the effect of AVE0118 on atrial refractoriness (ERP), left atrial vulnerability (LAV) and on left atrial monophasic action potentials (MAP) in pentobarbital anesthetized pigs in comparison to the selective I(Kr) blocker dofetilide in order to assess the therapeutic potential of the novel K(+) channel blocker for atrial fibrillation.

METHODS

Atrial ERP was determined with the S1-S2-stimulus method in the free walls of left and right atrium at 240, 300 and 400 ms basic cycle length (BCL). The inducibility of mostly nonsustained atrial tachyarrhythmias by the premature S2 extrastimulus, which is very high in the left pig atrium and referred to as LAV, was evaluated before and after drugs. Left atrial epicardial MAP was recorded to study the influence of the potassium channel blockers on the time course of repolarization. Left ventricular epicardial MAP, ERP and QT interval were measured to investigate a possible effect of AVE0118 on ventricular repolarization.

RESULTS

ERPs determined at 240, 300 and 400 ms BCL were significantly shorter in the left vs. right atrium (99+/-3, 106+/-4 and 113+/-3 ms vs. 133+/-4 ms, 142+/-4 and 149+/-5, respectively; p<0.001; n=21). AVE0118 administered i.v. dose-dependently prolonged the atrial ERP independent from rate and inhibited LAV (100% at 0.5 and 1 mg/kg) while having no effect at all on the corrected QT (QTc) interval. At 1 mg/kg (n=5) AVE0118 prolonged left vs. right atrial ERP by 49.6+/-4.1 ms vs. 37.7+/-9.7 ms (means+/-SEM of changes at 240, 300, and 400 ms BCL), respectively, corresponding to a relative increase of 53.2+/-6.2% vs. 27.6+/-6.8% (p<0.05 for percent increase of left vs. right atrial ERP). In a separate group of pigs (n=5) AVE0118 had no effect on left ventricular ERP at 333, 400 and 500 ms BCL and no effect on MAP duration and QT at 600 ms BCL. After 1 mg/kg of AVE0118 the atrial MAP was significantly prolonged already at 10% repolarization (P<0.05; n=7) reaching the maximum at 40% repolarization. In contrast to AVE0118 the effect of dofetilide (10 microg/kg) on atrial MAP started to become significant only at 60% repolarization (n=6) with a maximum increase at 90%. Dofetilide, which prolonged the QTc interval by 16.9% (P<0.001), had a significantly stronger effect on right (34.7+/-5 ms) vs. left atrial ERP (23.5+/-7 ms) at 300 ms BCL, respectively, but did not significantly inhibit LAV (14%; n=6).

CONCLUSION

The novel K(+) channel blocker AVE0118 prolonged atrial ERP and showed strong atrial antiarrhythmic efficacy with no apparent effect on ventricular repolarization in pigs in vivo.

Electrophysiological and antiarrhythmic effects of the novel I(Kur) channel blockers, S9947 and S20951, on left vs. right pig atrium in vivo in comparison with the I(Kr) blockers dofetilide, azimilide, d,l-sotalol and ibutilide

Inhibition of the cardiac Kv1.5 channel, the molecular base for the human cardiac ultrarapid delayed rectifier potassium current (I(Kur)), is considered a new promising atrial selective antiarrhythmic concept since this channel is presumed to contribute to atrial but not ventricular repolarization in the human heart. In a previous study in pigs we found clear baseline differences in refractoriness between left and right atrium with shorter effective refractory periods (ERPs) of the left atrium associated with a high left atrial vulnerability for tachyarrhythmias. In this newly established model we compared atrial and ventricular effects of two novel I(Kur) blockers, S9947 and S20951, with the I(Kr) blockers dofetilide, azimilide, ibutilide and d,l-sotalol. In pentobarbital anesthetized pigs (n=45) we determined ERPs in the free walls of both atria with the S1-S2-stimulus method at three basic cycle lengths (BCL 240/300/400 ms) and QTc-intervals. The incidence of atrial tachyarrhythmias triggered by the S2-extrastimulus of the left atrium was evaluated (referred to as left atrial vulnerability). In contrast to I(Kr) blockade, I(Kur) blockade had no effect on the QT-interval, but prolonged the atrial ERP. The I(Kur) blockers were significantly stronger on left atrial ERP, I(Kr) blockers on right atrial ERP (P<0.05 for all compounds tested). At 240 ms BCL the I(Kur) blocker S20951, 3 mg/kg, prolonged left vs. right atrial ERP by 28+/-5 ms vs. 12+/-3 ms and S9947, 3 mg/kg, by 45+/-7 ms vs. 19+/-6 ms. By contrast the effect of dofetilide, 10 microg/kg, was stronger on the right than left atrium (47+/-6 ms vs. 25+/-2 ms), a profile also found with azimilide (5 mg/kg, 43+/-3 ms vs. 17+/-3 ms), ibutilide (15 microg/kg, 70+/-10 ms vs. 29+/-4 ms) and d,l-sotalol (1.5 mg/kg, 57+/-6 ms vs. 36+/-4 ms). The I(Kur) blockers, S20951and S9947, significantly decreased left atrial vulnerability (-82% and -100%, respectively, P<0.01) in contrast to the selective I(Kr) blocker dofetilide (-14%; n.s.). In conclusion, I(Kur) and I(Kr) blockers showed substantial differences in their atrial and ventricular actions in pigs. I(Kr) blockers were stronger on right atrial ERP, I(Kur) blockers on left atrial ERP, suggesting interatrial differences in the expression of potassium channels. In contrast to selective I(Kr) blockade, I(Kur) blockade inhibited left atrial vulnerability and had no effect on the QT-interval. Thus, blockade of I(Kur) seems to be a promising atrial selective antiarrhythmic concept.

Inhibition of Na(+)/H(+) exchanger type 3 reduces duration of apnea induced by laryngeal stimulation in piglets

Reflexes from the larynx induce cessation of breathing in newborn animals. The magnitude of respiratory inhibition is inversely related to the level of central chemical input. Recent studies indicate that selective inhibition of Na(+)/H(+) exchanger type 3 (NHE3) activates CO(2)/H(+)-sensitive neurons, resembling the responses evoked by hypercapnic stimuli. Hence, the use of NHE3 inhibitors may reduce reflexly mediated respiratory depression and duration of apnea in the neonatal period. This possibility was examined in decerebrate, vagotomized, ventilated, and paralyzed piglets by testing the effects of i.v. administration of NHE3 blocker S8218 on the response of phrenic nerve amplitude, frequency, and duration of apnea induced by graded electrical stimulation of the superior laryngeal nerve. Superior laryngeal nerve stimulation caused a significant decrease in phrenic nerve amplitude, frequency, minute phrenic activity, and inspiratory time (all p < 0.01) that was proportional to the level of electrical stimulation. Increased levels of stimulation were more likely to induce apnea both during and after cessation of stimulation. NHE3 blocker S8218 reduced the superior laryngeal nerve stimulation-induced decrease in phrenic nerve amplitude, minute phrenic activity, and phrenic nerve frequency (all p < 0.05) and reduced superior laryngeal nerve stimulation-induced apnea and duration of poststimulation apnea (p < 0.05). In six other pigs the brain concentrations of S8218 were measured at different intervals after i.v. administration of the drug and were found to be higher in the brain tissue than plasma at all intervals. These findings suggest that the use of NHE3 blockers may decrease the duration of apnea and possibly reduce the pathophysiologic consequences of potentially life-threatening apnea in infants.

A novel inhibitor of the Na+/H+ exchanger type 3 activates the central respiratory CO2 response and lowers the apneic threshold

Cultured CO2-sensitive neurons from the ventrolateral medulla of newborn rats enhanced their bioelectric activity upon intracellular acidification induced by inhibition of the Na+/H+ exchanger type 3 (NHE3). Now we detected NHE3 also in the medulla oblongata of adult rabbits. Therefore, this animal model was employed to determine whether NHE3 inhibition also affects central respiratory chemosensitivity in vivo. Seven anesthetized (pentobarbital), vagotomized, paralyzed rabbits were artificially ventilated with O2-enriched air. From the phrenic nerve compound discharge, integrated burst amplitude (IPNA), respiratory rate (fR), and phrenic minute activity (IPNA. fR) were taken as measures of central respiratory rhythm and drive. Effects of potent NHE3 inhibition with the novel brain permeant substance S8218 were studied by comparing respiratory characteristics before and after up to 9.2 +/- 1.1 mg/kg cumulative drug application, yielding average plasma concentrations of 0.9 +/- 0.2 microg/ml. In response to S8218, the baseline level of IPNA. fR was significantly enhanced by an average of 51.0 +/- 6.4% (n = 27, p < 0.0001). The influence of NHE3 inhibition on the respiratory CO2 response was studied at plasma concentrations of S8218 maintained in the range of 0.3 microg/ml (10(-6) M). Although the metabolic acid-base status thereby remained widely unchanged, the group mean apneic threshold PaCO2 was significantly lowered by 0.45 +/- 0.11 kPa (n = 7, p < 0.01), whereby in four of seven animals even strong hyperventilation failed to suppress phrenic nerve rhythmicity completely. Likewise, S8218 significantly augmented IPNA. fR, in the range of PaCO2 between 1 and 6 kPa above threshold, by an average of 38.0 +/- 8.5% (n = 35, p < 0.0001). These in vivo results are compatible with the effects of NHE3 inhibition on chemosensitive brainstem neurons in vitro. Moreover, rhythmogenesis is supported through NHE3 inhibition by lowering the threshold PCO2 for central apnea.

NHE1-inhibitor cariporide prevents the transient reperfusion-induced shortening of the monophasic action potential after coronary ischemia in pigs

During myocardial ischemia intracellular acid load increases as a consequence of anaerobic metabolism. Exchange of excessive protons for sodium via the sodium proton exchanger type 1 (NHE1) is supposed to cause intracellular sodium accumulation. The NHE1 inhibitor cariporide has been shown to inhibit ischemia and reperfusion-induced ventricular fibrillation (VF) but the mechanisms are not fully understood. During early reperfusion transient shortening of the action potential has been reported, which renders the heart susceptible to reentrant arrhythmias. In anesthetized pigs subjected to 10 min of left circumflex coronary artery (LCX) occlusion and reperfusion we have investigated whether NHE1 is involved in reperfusion-induced shortening of the monophasic action potential (MAP) taken with an epicardial probe over the ischemic area. In control pigs (n = 7) a moderate decrease in the duration of the MAP at 50 % repolarization (MAPD50) occurred during ischemia reaching 78.8 +/- 5.0% of the pre-ischemic duration at 5 min (p < 0.01) and 87.3 +/- 7.6 % after 10 min. An additional, transient but marked shortening occurred during the first 2 min of reperfusion, which fully recovered after 4 min. At 50 sec of reperfusion MAPD50 fell to 53.1 +/- 8.2 % of the pre-ischemic value corresponding to 90.1 +/- 20.2 msec of reperfusion-induced shortening. Cariporide, 3 mg/kg i.v. 5 min before occlusion (n = 6), totally prevented reperfusion-induced MAP shortening while having no effect on MAPD50 during ischemia. In conclusion, our data suggest that the immediate, transient, but strong action potential shortening during early reperfusion after 10 min of coronary ischemia is due to the activity of the NHE1.

Differential effects of dofetilide, amiodarone, and class lc drugs on left and right atrial refractoriness and left atrial vulnerability in pigs

OBJECTIVES

Antiarrhythmic drugs have been shown to prolong right atrial refractoriness while data on the left atrium are not available. In pigs we have observed shorter effective refractory periods (ERP) of the left compared with the right atrium associated with a much higher left atrial vulnerability for tachyarrhythmias. Since this could suggest a different distribution of repolarizing ion channels in left and right atrium, we investigated whether antiarrhythmic drugs blocking different ion channels have a differential effect on left and right atrial ERP and left atrial vulnerability.

METHODS

In pentobarbital-anesthetized pigs (n=40) we measured and compared ERPs in both atria before and after different drugs with the S1-S2 extrastimulus method at three basic cycle lengths (BCL) and assessed the inducibility of atrial fibrillation/flutter (AF/AFL) by the premature S2 stimulus.

RESULTS

At the three BCL tested (240/300/400 ms) baseline ERPs were shorter in left vs. right atrium (112+/-2/124+/-2/129+/-2 ms vs. 147+/-2/163+/-2/167+/-2 ms, P<0.001). Mostly non-sustained AF/AFL induced by the S2 extrastimulus was very frequent in the left (68%) and nearly absent in the right atrium (3%). Only amiodarone, 5 mg/kg i.v., which showed a balanced increase of left and right atrial ERP (29+/-5/33+/-4/35+/-3% vs. 30+/-5/35+/-5/42+/-7%), decreased the inducibility of AF/AFL significantly (-72%, P<0.01). Dofetilide, 10 microg/kg i.v., had a stronger effect on right than left atrial ERP (36+/-4/39+/-5/46+/-10% vs. 23+/-2/22+/-7/22+/-5%, P<0.05), while flecainide, 1 mg/kg i.v., prolonged left more than right atrial ERP (58+/-15/36+/-7/40+/-7% vs. 26+/-5/24+/-5/21+/-4%, P<0.05) similar to 1 mg/ kg of propafenone (46+/-5/45+/-7/32+/-10% vs. 17+/-4/21+/-5/ 25+/-8%, P<0.05).

CONCLUSION

The shorter refractoriness of the left compared with the right atrium observed in pigs was associated with a high left atrial vulnerability for tachyarrhythmias, which was reduced only by amiodarone showing a balanced increase of left and right atrial ERP. Dofetilide was stronger on right atrial ERP, flecainide and propafenone on left atrial ERP. These differences suggest a differential distribution of repolarizing ion channels between left and right atrium with possible relevance for the antiarrhythmic efficacy of drugs.

Role of kinins in the control of renal papillary blood flow, pressure natriuresis, and arterial pressure

The present study evaluated the effects of blocking kinins with the bradykinin B(2) receptor antagonist Hoe140 on the relationship between renal perfusion pressure, papillary blood flow (PBF), and sodium excretion. To determine the relevance of renal kinins in the long-term control of arterial pressure, the effect of a chronic intrarenal infusion of Hoe140 on arterial pressure and sodium balance was also studied. PBF was not autoregulated in volume-expanded rats, and the administration of Hoe140 reduced PBF (-30%) and improved PBF autoregulation. The kinin antagonist also decreased sodium excretion (-35%) and blunted pressure natriuresis with no whole-kidney renal hemodynamic changes. These effects may be mediated through nitric oxide (NO), because in rats pretreated with N(G)-nitro-L-arginine methyl ester, Hoe140 had no additional effects on PBF or pressure natriuresis. A role for NO in mediating the renal response to Hoe140 is also supported by the finding that Hoe140 reduced basal urinary NO(3)(-)/NO(2)(-) excretion (-33%), and it blunted the arterial pressure-induced increase in NO(3)(-)/NO(2)(-) excretion, which is compatible with the idea that the pressure-natriuresis response may be mediated through kinins and NO. The importance of kinins in long-term regulation of arterial pressure is demonstrated by the severe arterial hypertension (172+/-6 mm Hg) induced during the chronic intrarenal infusion of Hoe140 associated with sodium and volume retention. These data suggest that renal kinins and NO may be a part of the renal mechanism coupling changes in arterial pressure with modifications in PBF and sodium excretion, therefore contributing to the long-term control of arterial pressure.

K(ATP) channel blocker HMR 1883 reduces monophasic action potential shortening during coronary ischemia in anesthetised pigs

ATP-sensitive potassium channels (KATP) open during myocardial ischemia. The ensuing repolarising potassium efflux shortens the action potential. Accumulation of extracellular potassium is able to partially depolarise the membrane, reducing the upstroke velocity of the action potential and thereby impairing impulse conduction. Both mechanisms are believed to be involved in the development of reentrant arrhythmias during cardiac ischemia. The sulfonylthiourea HMR 1883 (1-[[5-[2-(5-chloro-O-anisamido)ethyl]-methoxyphenyl]sulfonyl]-3-m ethylthiourea) was designed as a cardioselective KATP channel blocker for the prevention of arrhythmic sudden death in patients with ischemic heart disease. The aim of this study was to show that this compound, which has already shown antifibrillatory efficacy in dogs and rats, is able to inhibit ischemic changes of the action potential induced by coronary artery occlusion in anesthetised pigs. Action potentials were taken in situ with the technique of monophasic action potential (MAP) recording. In a control group (n=7), three consecutive occlusions of a small branch of the left circumflex coronary artery resulted in reproducible reductions in MAP duration and a decrease in upstroke velocity. In a separate group (n=7), HMR 1883 (3 mg/kg i.v.) significantly (P<0.05) reduced the ischemia-induced shortening of the MAP: during the first and second control occlusion of the coronary artery in the HMR 1883-group, MAP50 duration shortened from 218.5 +/- 3.0 ms to 166.7 +/- 3.3 ms and from 219.7 +/- 4.5 ms to 164.9 +/- 1.8 ms, respectively. After HMR 1883, during the third occlusion, MAP duration decreased from 226.9 +/- 3.6 ms to 205.3 +/- 4.3 ms only corresponding to 59% inhibition. HMR 1883 also improved the upstroke velocity of the MAP, which was depressed by ischemia: in the two preceding control occlusions ischemia prolonged the time to peak of the MAP, an index for upstroke velocity, from 10.83 +/- 0.43 ms to 39.42 +/- 1.60 ms and from 12.97 +/- 0.40 ms to 37.17 +/- 2.98 ms, respectively. With HMR 1883, time to peak during ischemia rose from 12.42 +/- 0.51 ms to 25.53+/-2.51 ms only, corresponding to an average inhibitory effect of 53.4%. The irregular repolarisation contour of the ischemic MAP was also improved. In conclusion, the present results indicate that HMR 1883 effectively blocks myocardial KATP channels during coronary ischemia in anesthetised pigs, preventing an excessive shortening of the action potential and improving excitation propagation.

ATP-sensitive potassium channel blocker HMR 1883 reduces mortality and ischemia-associated electrocardiographic changes in pigs with coronary occlusion

ATP-sensitive potassium (K(ATP)) channels are activated during myocardial ischemia. The ensuing potassium efflux leads to a shortening of the action potential duration and depolarization of the membrane by accumulation of extracellular potassium favoring the development of reentrant arrhythmias, including ventricular fibrillation. The sulfonylthiourea HMR 1883 was designed as a cardioselective blocker of myocardial K(ATP) channels for the prevention of arrhythmic sudden death in patients with ischemic heart disease. We investigated the effect of HMR 1883 on sudden cardiac arrhythmic death and electrocardiography (ECG) changes induced by 20 min of left anterior descending coronary artery occlusion in pentobarbital-anesthetized pigs. HMR 1883 (3 mg/kg i.v.) protected pigs from arrhythmic death (91% survival rate versus 33% in control animals; n = 12; p<.05). Ischemic areas were of a similar size. The compound had no effect on hemodynamics and ECG, including Q-T interval, under baseline conditions and no effect on hemodynamics during occlusion. In control animals, left anterior descending coronary artery occlusion lead to a prompt and significant depression of the S-T segment (-0.35 mV) and a prolongation of the Q-J time (+46 ms), the former reflecting heterogeneity in the plateau phase of the action potentials and the latter reflecting irregular impulse propagation and delayed ventricular activation. Both ischemic ECG changes were significantly attenuated by HMR 1883 (S-T segment, -0.14 mV; Q-J time, +15 ms), indicating the importance of K(ATP) channels in the genesis of these changes. In conclusion, the K(ATP) channel blocker HMR 1883, which had no effect on hemodynamics and ECG under baseline conditions, reduced the extent of ischemic ECG changes and sudden death due to ventricular fibrillation during coronary occlusion.

Amyloid beta-(1-40) stimulates cyclic GMP production via release of kinins in primary cultured endothelial cells

Increased beta-amyloid production is believed to play a central role in the pathogenesis of Alzheimer's disease. Amyloid is deposited not only in the brain of Alzheimer patients as senile plaques but also in the cerebral vessel wall leading to cerebral amyloid angiopathy. Freshly solubilised amyloid beta-(1-40) was previously reported to exert a vasoconstrictor effect. We investigated whether amyloid beta-(1-40) affects the nitric oxide (NO)/cyclic GMP pathway in primary cultured endothelial cells from bovine aorta and rat coronary microvessels. Surprisingly, a significant increase in cyclic GMP production after incubation with freshly dissolved amyloid beta-(1-40) was found. The stimulation of cyclic GMP production could be inhibited by the bradykinin B(2) receptor antagonist icatibant, the NO synthase inhibitor N-omega-nitro-L-arginine, the serine protease inhibitor 3, 4-dichloroisocoumarin and the selective plasma kallikrein inhibitor Pefabloc PK, suggesting activation of the plasma kallikrein-kinin system. This is supported by a three- to four-fold increase in kinins in the supernatant of both types of endothelial cells after incubation with amyloid beta-(1-40) at concentrations of 10(-7) and 10(-6) mol/l.

HMR 1883, a cardioselective K(ATP) channel blocker, inhibits ischaemia- and reperfusion-induced ventricular fibrillation in rats

Ventricular fibrillation (VF) is a major cause of sudden cardiac death in which myocardial ischemia plays a leading role. During ischaemia activation of ATP-sensitive potassium channels (K(ATP)) occurs, leading to potassium efflux from cardiomyocytes and shortening of the action potential favoring the genesis of ventricular fibrillation. In confirmation of this concept the sulfonylurea glibenclamide, which stimulates insulin release by inhibition of pancreatic K(ATP) channels, has been shown to inhibit VF in different models of ischaemia by inhibition of myocardial K(ATP) channels. HMR 1883 (1-[15-12-(5-chloro-o-anisamido)ethyl]-methoxyphenyl]sulfonyl]-3-m ethylthiourea) was designed as a cardioselective K(ATP) channel blocker. The aim of this study was to show that with this compound it is possible to separate the antifibrillatory from the insulin-releasing effect for the treatment of patients at risk of ischaemia-induced arrhythmias and sudden death. In the present study HMR 1883 reduced VF in Sprague-Dawley rats during prolonged ischaemia and also diminished mortality and the duration of VF in a separate reperfusion experiment at 3 mg/kg and 10 mg/kg with no effect on blood glucose or insulin. Glibenclamide, which was antifibrillatory at 0.3 mg/kg and 1 mg/kg, increased plasma insulin and lowered blood glucose already at a dose as low as 0.01 mg/kg. In conclusion, based on its antifibrillatory action and the absence of significant pancreatic effects at therapeutic doses, HMR 1883 is of potential clinical utility for the prevention of severe arrhythmias in patients with ischaemic heart disease.

Effect of icatibant, a bradykinin B2 receptor antagonist, on the development of experimental ulcerative colitis in mice

Dextran sulfate sodium-induced colitis in mice has been recognized as a model for human ulcerative colitis. Using this model, we carried out a study on the preventive effect of Icatibant, a bradykinin B2 receptor antagonist previously called HOE 140, on the development of colitis. Subcutaneous administration of Icatibant (0.3 or 1.5 mg/kg) significantly suppressed shortening of the large intestine and worsening of the general health. Oral administration of Icatibant (50 mg/kg) significantly suppressed shortening of the large intestine, the onset of diarrhea, and worsening of the general health. In addition, the oral treatment significantly inhibited the development of colitis that was observed histopathologically. These results indicate a role of BK in the development of dextran sulfate sodium-induced colitis in mice, and suggest that BK could be important in human ulcerative colitis.

The kinin antagonist hoe 140 reduces acute paw oedema in rats caused by carrageenan, bradykinin and kaolin

The present study aimed to evaluate the effect of Hoe 140, a BK receptor B(2) antagonist, on acute oedema induced by carrageenan, BK and kaolin in male Wistar Kyoto rats. Hoe 140 (0.2 mg/kg and 20 mg/kg) given ip caused significant (p<0.05 and p<0.01) inhibition of carrageenan and BK-induced paw oedema. This suggests that BK is the prime inflammatory mediator of carrageenan oedema, and that it is also a specific blocker of oedema caused by BK. Furthermore, Hoe 140 was found to be less effective in reducing kaolin-induced oedema in rats. This might reflect that BK is not a prime inflammatory mediator of kaolin-induced oedema. The possible significance of these findings is discussed.

The bradykinin B2 receptor antagonist Icatibant (HOE 140) corrects avid Na+ retention in rats with CCl4-induced liver cirrhosis: possible role of enhanced microvascular leakage

Avid Na+ retention is a hallmark of liver cirrhosis. The aim of this study was to investigate whether and how bradykinin is involved in Na+ retention in rats with CCl4-induced liver cirrhosis. To this end the bradykinin B2 receptor antagonist Icatibant (HOE 140) was used. On one hand, bradykinin has a renal natriuretic action. On the other hand, bradykinin is a potent mediator of both vasodilation and microvascular leakage. Both vascular mechanisms, which are reported for cirrhosis, could cause vascular underfilling and Na+ retention by activating the renin-angiotensin-aldosterone system. Icatibant normalised Na+ retention and reduced the hyperactivity of the renin-angiotensin-aldosterone system, suggesting a bradykinin-induced vascular disturbance. Icatibant had no significant effect on the mild hypotension which developed with CCl4 treatment. However, there was indirect evidence for enhanced microvascular leakage that was strongly inhibited by Icatibant. Our experimental results demonstrate that bradykinin is a key mediator of Na+ retention in liver cirrhosis and suggest that a bradykinin-induced increase in microvascular leakage is mainly responsible.

Kinins and cardioprotection

During the past decade it was recognised that kinins are potent endogenous vasoactive peptides with important cardioprotective actions which are of therapeutic relevance in the acute and chronic beneficial effects of ACE inhibitors. The effect of kinins is mediated through the release of autocoids from the endothelium, particularly nitric oxide (NO). In this review article the cardioprotective effects of kinins and their importance for the therapeutic effects of ACE inhibitors are highlighted.

Efficacy and tolerability of Icatibant (Hoe 140) in patients with moderately severe chronic bronchial asthma

Bradykinin (BK) has been identified as a mediator in human bronchial asthma. The current phase II study was designed as a multicentered, double blinded, randomized, placebo-controlled, parallel-group pilot study to investigate the efficacy of the B2 BK receptor antagonist Icatibant in adult patients with chronic asthma. Patients were treated t.i.d. with 900 micrograms or 3000 micrograms of nebulized Icatibant, or placebo. Treatment was for 4 weeks, followed by a 2-week placebo run-out. Icatibant was very well tolerated, and led to a dose-dependent improvement in objective pulmonary function tests (PFTs) measured by the investigators (e.g. FEV1 and PEFR). At 3 mg t.i.d., a statistically significant difference (p < 0.001) between Icatibant and placebo of about 10% was achieved after 4 weeks of treatment for all PFTs. At 900 micrograms t.i.d., the improvement in PFTs was smaller. By contrast, no clinically relevant improvement in global symptom score (nor a reduction of rescue medication) was found when compared with placebo. The observed improvement in objective PFTs started between weeks one and two, gradually increased until the end of active treatment, and slowly decreased during the placebo run-out phase, suggesting an anti-inflammatory effect. No acute bronchodilator effect was found. In conclusion, Icatibant showed a profile expected for an anti-inflammatory asthma drug.

Differences in acetylcholine- and bradykinin-induced vasorelaxation of the mesenteric vascular bed in spontaneously hypertensive rats of different ages

The present study examined whether alterations of endothelium-dependent vasorelaxation in spontaneously hypertensive rats (SHR) in response to the endothelium-dependent vasodilators acetylcholine and bradykinin ran parallel. We tried to find out the age at which endothelium-dependent vasorelaxation in response to each agonist became impaired and compared three different groups of SHR aged 7, 21 and 51 weeks. To be able to separate hypertension-induced alterations from age-dependent changes age-matched normotensive Wistar rats were included. Endothelium-dependent vasorelaxation was studied in the mesenteric vascular bed precontracted with noradrenaline, a typical resistance vessel, which showed relaxation to both acetylcholine and bradykinin, and the precontracted thoracic aorta, which only responded to acetylcholine. There were major differences in the agonist-dependent vasorelaxation between bradykinin and acetylcholine in SHR as a function of age. A surprising finding was that acetylcholine-induced relaxation was preserved, even slightly improved not only in young SHR (7 weeks) with developing hypertension but also in adult SHR (21 weeks) with established hypertension, which can be interpreted as a compensatory mechanism. As expected, in old SHR (51 weeks) acetylcholine-induced vasorelaxation was impaired as a consequence of the detrimental effects of long-term hypertension on endothelium. The parallel changes observed with acetylcholine in the mesenteric vascular bed and thoracic aorta provided mutual confirmation. In clear contrast to acetylcholine bradykinin-induced vasorelaxation was already imparied in young SHR with developing hypertension suggesting that bradykinin-induced vasorelaxation is either much more sensitive to detrimental effects of (even slightly) increased blood pressure or, more likely, that there is a basic deficiency in the action of bradykinin in SHR. Thus, our study allows to conclude that impairment of acetylcholine-induced endothelium-dependent vasorelaxation in the mesenteric vascular bed of SHR is a secondary phenomenon developing as a consequence of long-term hypertension while the impaired bradykinin-induced vasorelaxation seems to be a primary phenomenon that could be closely related to the development of hypertension.

Inhibition of rats adjuvant arthritis by a bradykinin antagonist Hoe 140 and its influence on kallikreins

1. This study examines the effect of Hoe 140, a bradykinin (BK) 2 receptor antagonist, indomethacin and prednisolone on chronic adjuvant arthritis of the knee in rats. We also evaluated the influence of Hoe 140 on BK-forming enzymes in the synovial and paw tissues. 2. Adjuvant arthritis was induced in male Sprague-Dawley rats in the right knee by injecting 0.05 ml of a fine suspension of heat-killed Mycobacterium tubercle bacilli in liquid paraffin (5 mg/ml). 3. Hoe 140 (1.5 mg/kg i.p.), indomethacin (2.5 mg/kg orally) and prednisolone (3.0 mg/kg orally) administration for 9 days resulted in significant suppression of knee joint swelling. Plasma and tissue kallikrein levels were raised (P < 0.01) in the synovial and paw tissues of adjuvant arthritic rats. Hoe 140 treatment reduced (P < 0.05) tissue kallikrein but increased (P < 0.01) plasma kallikrein levels in synovial tissue. 4. Hoe 140 treatment did not alter (P > 0.05) the raised plasma and tissue kallikrein levels in the paw tissue. The findings indicate that Hoe 140 may be a useful anti-inflammatory agent and BK plays a major role in this adjuvant-induced arthritis model.

Kinin receptor antagonists: unique probes in basic and clinical research

The availability of potent and stable bradykinin antagonists has had a tremendous impact on kinin research. This article reviews the current status of research on kinin antagonists, describes their chemical properties, and delineates recent advances that have occurred with the advent of the second generation of kinin antagonists. The data collected with these antagonists support the assumption that kinins are implicated in inflammation and tissue injury as endogenous agents. Their importance, however, is not limited to the role as mediators of tissue injury and inflammation, as kinin antagonists have enabled the identification kinins as potential endogenous cardioprotective substances, also contributing to the effects of angiotensin converting enzyme inhibitors. Clinical studies are currently being performed in asthma, postoperative pain, anaphlyactoid reactions during low density lipoprotein apheresis, systemic inflammatory response syndrome, and suspected sepsis, head injury, and hantavirus infections to investigate the utility of kinin antagonists as therapeutic agents.

The bradykinin B2 receptor antagonist WIN 64338 inhibits the effect of des-Arg9-bradykinin in endothelial cells

WIN 64338 (phosphonium, [[4-[[2-[[bis(cyclohexylamino) methylene] amino]-3-(2-naphthalenyl) 1-oxopropyl]amino]-phenyl]- tributyl, chloride, monohydrochloride) is the first potent nonpeptide competitive bradykinin B2 receptor antagonist as shown in classical pharmacological preparations with no activity in the rabbit aorta stimulated by the bradykinin B1 receptor agonist des-Arg9-bradykinin. In primary cultured bovine aortic endothelial cells, both bradykinin and des-Arg9-bradykinin stimulate the production of intracellular cyclic GMP, an index for the production of nitric oxide. Surprisingly, WIN 64338 did not inhibit bradykinin but abolished the effect of des-Arg9-bradykinin suggesting that kinin receptor antagonists do not necessarily discriminate between kinin receptor subtypes in an identical way in different tissues and species.

Effect of Hoe 140 on bradykinin-induced bronchoconstriction in anesthetized guinea pigs

We have investigated the efficacy of the novel, highly potent, and stable B2 bradykinin (BK) antagonist Hoe 140 against BK-induced bronchoconstriction in guinea pigs via whole body plethysmography and compared different routes of administration. Our results clearly demonstrate that Hoe 140 is highly potent at inhibiting bronchoconstriction induced by either intravenous (i.v.) or inhaled BK. Intravenous BK was strongly inhibited by i.v. Hoe 140 (ID50 13.4 pmol/kg), and less by aerosolized Hoe 140 (ID50 1.34 nmol/kg). Aerosolized BK (235 nmol/kg) was strongly inhibited by 0.1 nmol/kg of aerosolized Hoe 140 given 30 min before. Hoe 140 is the first BK antagonist to effectively inhibit the bronchoconstrictor effect of aerosolized BK. The equieffective i.v. dose of Hoe 140, however, as about 100-fold higher. From the discrepancy in efficacy of Hoe 140 against i.v. and aerosolized BK, it was concluded that i.v. BK has no direct effect on the lung, in contrast to inhaled BK. Moreover, the high potency of Hoe 140 in the guinea pig lung does not confirm the hypothesis of a B3 BK receptor. Based on its high potency and good tolerability, Hoe 140 is appropriate to evaluate the role of BK in human airway diseases.