Induction of cluster headache after opening of adenosine triphosphate-sensitive potassium channels: a randomized clinical trial.

ABSTRACT: Activation of adenosine triphosphate-sensitive potassium (K ATP ) channels has been implicated in triggering migraine attacks. However, whether the opening of these channels provoke cluster headache attacks remains undetermined. The hallmark of cluster headache is a distinct cyclical pattern of recurrent, severe headache episodes, succeeded by intervals of remission where no symptoms are present. In our study, we enrolled 41 participants: 10 with episodic cluster headaches during a bout, 15 in the attack-free remission period, and 17 diagnosed with chronic cluster headaches. Over 2 distinct experimental days, participants underwent a continuous 20-minute infusion of levcromakalim, a K ATP channel opener, or a placebo (isotonic saline), followed by a 90-minute observational period. The primary outcome was comparing the incidence of cluster headache attacks within the postinfusion observation period between the levcromakalim and placebo groups. Six of 10 participants (60%) with episodic cluster headaches in bout experienced attacks after levcromakalim infusion, vs just 1 of 10 (10%) with placebo ( P = 0.037). Among those in the remission phase, 1 of 15 participants (7%) reported attacks after levcromakalim, whereas none did postplacebo ( P = 0.50). In addition, 5 of 17 participants (29%) with chronic cluster headache had attacks after levcromakalim, in contrast to none after placebo ( P = 0.037). These findings demonstrate that K ATP channel activation can induce cluster headache attacks in participants with episodic cluster headaches in bout and chronic cluster headache, but not in those in the remission period. Our results underscore the potential utility of K ATP channel inhibitors as therapeutic agents for cluster headaches.

PACAP signaling is not involved in GTN- and levcromakalim-induced hypersensitivity in mouse models of migraine.

BACKGROUND: Calcitonin gene-related peptide (CGRP) antagonizing drugs represents the most important advance in migraine therapy for decades. However, these new drugs are only effective in 50-60% of patients. Recent studies have shown that the pituitary adenylate cyclase-activating peptide (PACAP38) pathway is independent from the CGRP signaling pathway. Here, we investigate PACAP38 signaling pathways in relation to glyceryl trinitrate (GTN), levcromakalim and sumatriptan. METHODS: In vivo mouse models of PACAP38-, GTN-, and levcromakalim-induced migraine were applied using tactile sensitivity to von Frey filaments as measuring readout. Signaling pathways involved in the three models were dissected using PACAP-inhibiting antibodies (mAbs) and sumatriptan. RESULTS: We showed that PACAP mAbs block PACAP38 induced hypersensitivity, but not via signaling pathways involved in GTN and levcromakalim. Also, sumatriptan has no effect on PACAP38-induced hypersensitivity relevant to migraine. This is the first study testing the effect of a PACAP-inhibiting drug on GTN- and levcromakalim-induced hypersensitivity. CONCLUSIONS: Based on the findings in our mouse model of migraine using migraine-inducing compounds and anti-migraine drugs, we suggest that PACAP acts via a distinct pathway. Using PACAP38 antagonism may be a novel therapeutic target of interest in a subgroup of migraine patients who do not respond to existing therapies.

A c-Fos activation map in nitroglycerin/levcromakalim-induced models of migraine.

BACKGROUND: Chronic migraine is a common and highly disabling disorder. Functional MRI has indicated that abnormal brain region activation is linked with chronic migraine. Drugs targeting the calcitonin gene-related peptide (CGRP) or its receptor have been reported to be efficient for treating chronic migraine. The CGRP signaling was also shared in two types of chronic migraine models (CMMs). However, it remains unclear whether the activation of specific brain regions could contribute to persistent behavioral sensitization, and CGRP receptor antagonists relieve migraine-like pain in CMMs by altering specific brain region activation. Therefore, it's of great interest to investigate brain activation pattern and the effect of olcegepant (a CGRP receptor-specific antagonist) treatment on alleviating hyperalgesia by altering brain activation in two CMMs, and provide a reference for future research on neural circuits. METHODS: Repeated administration of nitroglycerin (NTG) or levcromakalim (LEV) was conducted to stimulate human migraine-like pain and establish two types of CMMs in mice. Mechanical hypersensitivity was evaluated by using the von Frey filament test. Then, we evaluated the activation of different brain regions with c-Fos and NeuN staining. Olcegepant was administered to explore its effect on mechanical hyperalgesia and brain region activation. RESULTS: In two CMMs, acute and basal mechanical hyperalgesia was observed, and olcegepant alleviated mechanical hyperalgesia. In the NTG-induced CMM, the medial prefrontal cortex (mPFC), anterior cingulate cortex (ACC), and the caudal part of the spinal trigeminal nucleus (Sp5c) showed a significant increase of c-Fos expression in the NTG group (p < 0.05), while pre-treatment with olcegepant reduced c-Fos expression compared with NTG group (p < 0.05). No significant difference of c-Fos expression was found in the paraventricular thalamic nucleus (PVT) and ventrolateral periaqueductal gray (vlPAG) between the vehicle control and NTG group (p > 0.05). In the LEV-induced CMM, mPFC, PVT, and Sp5c showed a significant increase of c-Fos expression between vehicle control and LEV group, and olcegepant reduced c-Fos expression (p < 0.05). No significant difference in c-Fos expression was found in vlPAG and ACC (p > 0.05). CONCLUSIONS: Our study demonstrated the activation of mPFC and Sp5c in two CMMs. Olcegepant may alleviate hyperalgesia of the hind paw and periorbital area by attenuating brain activation in CMMs.

ATP-Sensitive Potassium Channels in Migraine: Translational Findings and Therapeutic Potential.

Globally, migraine is a leading cause of disability with a huge impact on both the work and private life of affected persons. To overcome the societal migraine burden, better treatment options are needed. Increasing evidence suggests that ATP-sensitive potassium (KATP) channels are involved in migraine pathophysiology. These channels are essential both in blood glucose regulation and cardiovascular homeostasis. Experimental infusion of the KATP channel opener levcromakalim to healthy volunteers and migraine patients induced headache and migraine attacks in 82-100% of participants. Thus, this is the most potent trigger of headache and migraine identified to date. Levcromakalim likely induces migraine via dilation of cranial arteries. However, other neuronal mechanisms are also proposed. Here, basic KATP channel distribution, physiology, and pharmacology are reviewed followed by thorough review of clinical and preclinical research on KATP channel involvement in migraine. KATP channel opening and blocking have been studied in a range of preclinical migraine models and, within recent years, strong evidence on the importance of their opening in migraine has been provided from human studies. Despite major advances, translational difficulties exist regarding the possible anti-migraine efficacy of KATP channel blockage. These are due to significant species differences in the potency and specificity of pharmacological tools targeting the various KATP channel subtypes.

Effect of Cromakalim Prodrug 1 (CKLP1) on Aqueous Humor Dynamics and Feasibility of Combination Therapy With Existing Ocular Hypotensive Agents.

Purpose: Cromakalim prodrug 1 (CKLP1) is a water-soluble ATP-sensitive potassium channel opener that has shown ocular hypotensive properties in ex vivo and in vivo experimental models. To determine its mechanism of action, we assessed the effect of CKLP1 on aqueous humor dynamics and in combination therapy with existing ocular hypotensive agents. Methods: Outflow facility was assessed in C57BL/6 mice by ex vivo eye perfusions and by in vivo constant flow infusion following CKLP1 treatment. Human anterior segments with no trabecular meshwork were evaluated for effect on pressure following CKLP1 treatment. CKLP1 alone and in combination with latanoprost, timolol, and Rho kinase inhibitor Y27632 were evaluated for effect on intraocular pressure in C57BL/6 mice and Dutch-belted pigmented rabbits. Results: CKLP1 lowered episcleral venous pressure (control: 8.9 ± 0.1 mm Hg versus treated: 6.2 ± 0.1 mm Hg, P < 0.0001) but had no detectable effect on outflow facility, aqueous humor flow rate, or uveoscleral outflow. Treatment with CKLP1 in human anterior segments without the trabecular meshwork resulted in a 50% ± 9% decrease in pressure, suggesting an effect on the distal portion of the conventional outflow pathway. CKLP1 worked additively with latanoprost, timolol, and Y27632 to lower IOP, presumably owing to combined effects on different aspects of aqueous humor dynamics. Conclusions: CKLP1 lowered intraocular pressure by reducing episcleral venous pressure and lowering distal outflow resistance in the conventional outflow pathway. Owing to this unique mechanism of action, CKLP1 works in an additive manner to lower intraocular pressure with latanoprost, timolol, and Rho kinase inhibitor Y27632.

The KATP channel in migraine pathophysiology: a novel therapeutic target for migraine.

BACKGROUND: To review the distribution and function of KATP channels, describe the use of KATP channels openers in clinical trials and make the case that these channels may play a role in headache and migraine. DISCUSSION: KATP channels are widely present in the trigeminovascular system and play an important role in the regulation of tone in cerebral and meningeal arteries. Clinical trials using synthetic KATP channel openers report headache as a prevalent-side effect in non-migraine sufferers, indicating that KATP channel opening may cause headache, possibly due to vascular mechanisms. Whether KATP channel openers can provoke migraine in migraine sufferers is not known. CONCLUSION: We suggest that KATP channels may play an important role in migraine pathogenesis and could be a potential novel therapeutic anti-migraine target.

Involvement of ATP-sensitive potassium channels and the opioid system in the anticonvulsive effect of zolpidem in mice.

Zolpidem is a hypnotic medication that mainly exerts its function through activating γ-aminobutyric acid (GABA)A receptors. There is some evidence that zolpidem may have anticonvulsive effects. However, the mechanisms underlying this effect have not been elucidated yet. In the present study, we used the pentylentetrazole (PTZ)-induced generalized seizure model in mice to investigate whether zolpidem can affect seizure threshold. We also further evaluated the roles of ATP-sensitive potassium (KATP) channels as well as µ-opioid receptors in the effects of zolpidem on seizure threshold. Our data showed that zolpidem in a dose-dependent manner increased the PTZ-induced seizure threshold. The noneffective (i.e., did not significantly alter the PTZ-induced seizure threshold by itself) doses of KATP channel blocker (glibenclamide) and nonselective opioid receptor antagonist (naloxone) were able to inhibit the anticonvulsive effect of zolpidem. Additionally, noneffective doses of either KATP channel opener (cromakalim) or nonselective µ-opioid receptor agonist (morphine) in combination with a noneffective dose of zolpidem exerted a significant anticonvulsive effect on PTZ-induced seizures in mice. A combination of noneffective doses of naloxone and glibenclamide, which separately did not affect zolpidem effect on seizure threshold, inhibited the anticonvulsive effects of zolpidem. These results suggest a role for KATP channels and the opioid system, alone or in combination, in the anticonvulsive effects of zolpidem.

Ocular Hypotensive Effects of the ATP-Sensitive Potassium Channel Opener Cromakalim in Human and Murine Experimental Model Systems.

Elevated intraocular pressure (IOP) is the most prevalent and only treatable risk factor for glaucoma, a leading cause of irreversible blindness worldwide. Unfortunately, all current therapeutics used to treat elevated IOP and glaucoma have significant and sometimes irreversible side effects necessitating the development of novel compounds. We evaluated the IOP lowering ability of the broad spectrum KATP channel opener cromakalim. Cultured human anterior segments when treated with 2 µM cromakalim showed a decrease in pressure (19.33 ± 2.78 mmHg at 0 hours to 13.22 ± 2.64 mmHg at 24 hours; p<0.001) when compared to vehicle treated controls (15.89 ± 5.33 mmHg at 0 h to 15.56 ± 4.88 mmHg at 24 hours; p = 0.89). In wild-type C57BL/6 mice, cromakalim reduced IOP by 18.75 ± 2.22% compared to vehicle treated contralateral eyes (17.01 ± 0.32 mmHg at 0 hours to 13.82 ± 0.37 mmHg at 24 hours; n = 10, p = 0.002). Cromakalim demonstrated an additive effect when used in conjunction with latanoprost free acid, a common ocular hypotensive drug prescribed to patients with elevated IOP. To examine KATP channel subunit specificity, Kir6.2(-/-) mice were treated with cromakalim, but unlike wild-type animals, no change in IOP was noted. Histologic analysis of treated and control eyes in cultured human anterior segments and in mice showed similar cell numbers and extracellular matrix integrity within the trabecular meshwork, with no disruptions in the inner and outer walls of Schlemm's canal. Together, these studies suggest that cromakalim is a potent ocular hypotensive agent that lowers IOP via activation of Kir6.2 containing KATP channels, its effect is additive when used in combination with the commonly used glaucoma drug latanoprost, and is not toxic to cells and tissues of the aqueous humor outflow pathway, making it a candidate for future therapeutic development.

Blocking of the ATP sensitive potassium channel ameliorates the ischaemia-reperfusion injury in the rat testis.

There is increasing evidence that the effects of administered ATP sensitive potassium (KATP ) channel openers or blockers during ischaemia are still controversial in many organs/tissues. Testicular torsion detorsion which causes ischaemia-reperfusion (IR) injury, cannot be predicted, thus an effective drug should be administered during or after the ischaemia. The aim of this study was to examine whether the administration of KATP channel openers or blockers during ischaemia ameliorates IR injury in the testis. Eight-week-old male Sprague-Dawley rats were subjected to 2 h right testicular ischaemia followed by 24 h reperfusion. The selective mitochondrial (mito) KATP channel blocker, 5-hydroxydecanoate (5-HD) (40 mg/kg), the non-selective KATP channel blocker glibenclamide (5 mg/kg), the selective mito KATP channel opener diazoxide (10 mg/kg) and the non-selective KATP channel opener cromakalim (300 µg/kg) were administered intraperitoneally 15 min prior to the ischaemia or 75 min after the induction of ischaemia. Tissue damage was evaluated by malondialdehyde concentration, myeloperoxidase activity, histological evaluation and TdT-mediated dUTP nick end labelling assay in the testis. There was a significant increase in oxidative stress, neutrophil infiltration, histological damage and apoptosis in the testicular IR model. A significant reduction in the testicular IR injury was observed with the administration of glibenclamide, but not 5-HD, diazoxide or cromakalim during ischaemia. The administration of non-selective KATP channel blocker glibenclamide ameliorated the testicular IR injury. On the other hand, the selective mito KATP channel blocker, 5-HD and KATP channel openers did not reduce the testicular IR injury. These data suggest that blocking of the membrane KATP channel may have a protective effect during the testicular ischaemia. Glibenclamide could be an effective drug to manage the post-ischaemic injury caused by the testicular torsion-detorsion.

The role of K ATP channels on ischemia-reperfusion injury in the rat testis.

AIMS: To investigate the participation of K(ATP) channels on the ischemia-reperfusion (IR)-induced apoptosis in the rat testis. MAIN METHODS: Eight-week-old male Sprague-Dawley rats were divided into three groups: control and IR rats without or with cromakalim (300 µg/kg intraperitoneally), 30 min before the induction of ischemia. The right testicular artery and vein were clamped to induce ischemia in the testis. Sixty minutes after the ischemia, a 24h period of reperfusion followed. Then, expressions of K(IR)6.1, K(IR)6.2, caspase-3, PARP, Fas, FasL, and K(IR)6.1 and K(IR)6.2 mRNAs were investigated by Western blot analyses and real-time PCR methods, respectively. Furthermore, testicular tissues were processed for histological evaluation and TUNEL staining. KEY FINDINGS: Expressions of K(IR)6.1 protein and mRNA were more than 10-fold of those of K(IR)6.2 protein and mRNA in the testis. IR significantly increased the expressions of K(IR)6.1 protein and mRNA as well as K(IR)6.2 mRNA, caspase-3, and TUNEL index in the testis compared to the control. PARP expressions were significantly lower in the IR group than those of the control. Histologically, severe acute germ cell damage was observed in the IR testis. Treatment with cromakalim ameliorated these parameters compared to the non-treated IR group. There were no significant differences on Fas, FasL and protein level of K(IR)6.2 expressions between any of the groups. SIGNIFICANCE: Treatment with cromakalim has a protective effect against IR-induced testicular damage via activating K(ATP) channels. This is the first study to give evidence for the advantageous effect of cromakalim in the germ cell-specific apoptosis induced by testicular IR.

Eicosapentaenoic acid reduces ischemic ventricular fibrillation via altering monophasic action potential in pigs.

Although high intake of n-3 fatty acids is associated with reduced mortality of patients with ischemic heart disease, especially reduction in sudden cardiac death (SCD), the detailed mechanisms remain to be elucidated. Thus, the present study was designed to examine whether long-term treatment with eicosapentaenoic acid (EPA), a major component of n-3 fatty acids, reduces ischemia-induced ventricular fibrillation (VF) in pigs in vivo, and if so, what molecular mechanisms are involved. Male pigs were treated with either a control chow (control group) or a control chow plus EPA (600 mg/kg/day, PO, EPA group) for 3 weeks and were subjected to myocardial ischemia for 90 min (n=8 each) with measurement of the monophasic action potential (MAP), as a marker of ventricular electrophysiological activities. The EPA treatment significantly attenuated the occurrence of VF (control 5.1±1.7 vs. EPA 1.5±0.8 times/animal, P<0.05) and markedly reduced the mortality (control 50% vs. EPA 0%, P<0.05), with the attenuation of MAP duration shortening during ischemia (control -28.1±3.0% vs. EPA -18.2±1.4%, P<0.05). These beneficial effects of EPA were abolished by pre-treatment with cromakalim, a K(ATP) channel opener (0.3 µg/kg/min, IC). Furthermore, EPA significantly inhibited the mRNA and protein expression of Kir6.2, a major component of sarcolemmal K(ATP) channels, in both the ischemic region and non-ischemic regions. These results indicate that long-term treatment with EPA reduces ischemia-induced VF and SCD in pigs in vivo, for which attenuation of MAP duration shortening may be involved.

Nicorandil ameliorates ischaemia-reperfusion injury in the rat kidney.

BACKGROUND AND PURPOSE: Nicorandil, an ATP-sensitive potassium (K(ATP) ) channel opener and nitric oxide donor, is used in the treatment of angina and acute heart failure. Here we investigated the effects of two K(ATP) channel openers, nicorandil and cromakalim on ischaemia reperfusion (I-R) injury in the kidney. EXPERIMENTAL APPROACH: Right nephrectomy was performed in 8-week-old male Sprague-Dawley rats and they were then divided into six groups: control group; I-R, including 30 min of left renal ischaemia followed by 24 h of reperfusion; I-R groups plus nicorandil 3 or 10 mg·kg⁻¹ i.p.; and I-R groups plus cromakalim 100 or 300 µg·kg⁻¹ i.p. After reperfusion, renal function was estimated by serum creatinine (SCr), urinary albumin:creatinine ratio (ACR) and urinary ß2-microglobulin (ß2-MG). Levels of K(ATP) channel subtypes were investigated by Western blot. Kidney sections were stained for 4-hydroxy-2-nonenal and 8-hydroxy-2'-deoxyguanosine. KEY RESULTS: Renal I-R induced significant increases in SCr, ACR and ß2-MG levels compared with the control animals. Treatment with K(ATP) channel openers reduced urinary ß2-MG levels, raised by I-R. Both K(IR) 6.1 and K(IR) 6.2 channels were expressed. Expression of K(IR) 6.2 channels in the I-R group was lower than in the control group, which was restored to normal by treatment with K(ATP) channel openers. Histologically, severe acute tubular damage was observed in the I-R kidney and this damage was ameliorated by K(ATP) channel openers, dose-dependently. CONCLUSIONS AND IMPLICATIONS: ATP-sensitive potassium channel openers protected against proximal tubule damage after I-R injury. Nicorandil could represent a powerful additional component in the treatment of patients undergoing partial nephrectomy or renal transplantation.

Interaction of morphine and potassium channel openers on experimental models of pain in mice.

Combination of opioid and potassium channel openers holds immense potential for the treatment for most acute and chronic pain. Therefore, the study was performed to assess the interaction between morphine and K(+) -channel openers. Swiss albino mice of either sex weighing between 25 and 30 g were used for the study. The study assesses the interaction between morphine and K(+) -channel openers (cromakalim, diazoxide and minoxidil), when administered intraperitoneally, using formalin and tail-flick tests in mice. Both morphine and K(+) -channel openers produced significant antinociception at higher doses in both the behavioral tests. Lower doses of morphine and K(+) -channel openers had no significant effect on tail-flick latency, while the same drugs had significant antinociceptive effect on formalin test. The combination of lower doses of morphine and K(+) -openers was observed to have significant antinociceptive effect in both the behavioral tests. Administration of naloxone prior to morphine or K(+) -channel openers antagonized the analgesic effect of morphine but not of K(+) -channel openers, whereas prior administration of glibenclamide antagonized the effect of both morphine and K(+) -channel openers. The study, therefore, suggests that the common site of action of morphine and K(+) -channel openers is at the levels of K(+) -channels rather than at the level of receptors. However, such interaction depends on the differential sensitivity to different pain stimulus.

ATP-sensitive potassium channels contribute to the time-dependent alteration in the pentylenetetrazole-induced seizure threshold in diabetic mice.

Although there is evidence that diabetes affects seizure susceptibility, the underlying mechanism has not been completely understood. Several studies also suggest a pivotal role for K(ATP) channels in the seizure modulation. The aim of the present study was to evaluate the seizure threshold induced by pentylenetetrazole in diabetic mice at different times (3 days, 1-8 weeks) after induction of diabetes with streptozocin and to examine the possible role of ATP-sensitive potassium (K(ATP)) channels in this manner. Our data showed a time-dependent alteration in the threshold in diabetic mice, reaching a peak on week 2 after streptozocin injection and declining significantly afterwards. The seizure threshold in 8-week diabetic mice was even lower than control levels, though the difference was not significant. The K(ATP) channel opener cromakalim (0.1-30microg/kg, i.p.) significantly increased the seizure threshold in control mice. Although the K(ATP) channel blocker glibenclamide (0.5, 1mg/kg) had no effect, it prevented the effects of the potent dose of cromakalim (30microg/kg) on seizure threshold in control mice. Glibenclamide (1mg/kg, i.p.) also decreased the seizure threshold in 2-week diabetic mice to the control levels which was blocked by pre-treatment with cromakalim (10microg/kg, i.p.). Cromakalim (10microg/kg, i.p.) significantly increased the seizure threshold in 8-week diabetic mice which was inhibited by pre-treatment with glibenclamide (1mg/kg, i.p.). We demonstrated a time-dependent alteration in the pentylenetetrazole-induced seizure threshold in diabetic mice. This phenomenon might be due to the probable alteration in the K(ATP) channel functioning during the diabetic condition.

Antiulcer activity of levcromakalim and nicorandil in albino rats: a comparative study.

The objective of the present study was to investigate and compare the antiulcer effect of potassium channel openers, nicorandil and levcromakalim in the models of ulcer induced by pylorus ligation, aspirin and water immersion plus restraint stress in albino rats. Levcromakalim (250 microg/kg) and nicorandil (10 mg/kg) were administered intraduodenally immediately after pylorus ligation. Ulcer index was determined and gastric juice was subjected to analysis of total acid output (TAO) and pH. In aspirin-induced gastric ulcer model, the drugs were administered orally 30 min prior to noxious challenge, and in water immersion restraint stress model, the drugs were administered orally and ulcer index was determined. A significant reduction in ulcer index was observed after treatment with both potassium channel openers in all the gastric ulcer models. In pylorus-ligated rats, a significant decrease in TAO was noted. The conclusion is that potassium channel openers possess antiulcer activity. Antiulcer activity of levcromakalim is better than nicorandil but comparable to that of cimetidine. The antiulcer action of potassium channel openers is mediated partially by a decrease in gastric acid secretion, increase in gastric mucosal resistance and improvement in gastric mucosal blood flow.

Effects of chronic treatment with cromakalim and glibenclamide in alloxan-induced diabetic rats.

We have studied the effects of chronic treatment with cromakalim (75 ug kg(-1) per day) and glibenclamide (20 mg kg(-1) per day) in alloxan-induced diabetic rats. Injection of alloxan (60 mg kg(-1)/i.v., single dose) produced a significant increase in the blood pressure, bradycardia, hyperglycemia, hypoinsulinemia, hyperlipidemia, hypothyroidism and depression in left ventricular developed pressure (LVDP). While glibenclamide significantly prevented alloxan-induced hyperglycemia and hypoinsulinaemia, it failed to alter hypertension, bradycardia, hypertriglyceridaemia and hypercholesterolemia. Treatment with cromakalim-prevented hypertension and bradycardia, but not the hyperglycemia or hypoinsulinaemia. Co-administration of cromakalim with glibenclamide antagonized the effect of glibenclamide on these parameters. Cromakalim treatment also prevented alloxan-induced hypercholesterolemia and hypertriglyceridaemia. It also produced a significant increase in serum T(3) and T(4) levels. Glibenclamide did not significantly alter alloxan-induced hypothyroidism. In conclusion our data suggest that cromakalim and glibenclamide produce some metabolic effects that are either not related to K(ATP) channel modulation or may involve different sub-types of potassium channels. Further glibenclamide when combined with cromakalim may not be beneficial in a condition when diabetes mellitus and hypertension co-exits.

The effect of pretreatment with ischaemic preconditioning or cromakalim on perfusion in skeletal muscle during ischaemia-reperfusion injury.

BACKGROUND: Ischaemia-induced damage of skeletal muscle may lead to side effects in orthopaedic and reconstructive surgery where tourniquet ischaemia is applied to ensure a bloodless operative field. In this study we investigated the effect of ischaemia-reperfusion injury with and without preconditioning by studying the skeletal muscle microcirculation. A further aim was to establish whether ischaemic preconditioning or pretreatment with cromakalim, a potassium channel opener reduces ischaemia-reperfusion injury. METHODS: Twenty-eight Wistar rats were randomised into four groups (n=7 per group). Group 1, control with no treatment; Group 2, two and a half hours tourniquet ischaemia followed by two hours of reperfusion to the left hindlimb. Furthermore, we pre-treated two groups prior to the ischaemia-reperfusion period; Group 3 with three short cycles of ischaemia-reperfusion (5'/5') and Group 4 pre treated with cromakalim (100 microg/kg bw). We monitored the gastrocnemius muscle blood flow in vivo. RESULTS: There were no significant changes in the skeletal muscle microcirculation and temperature at the baseline in the four groups (p=0.110). In the ischaemic reperfusion, ischaemia preconditioning and cromakalim groups, the recorded skeletal muscle microcirculation during ischaemia decreased significantly (p<0.001) with respect to the baseline. In Group 2 the microcirculation recovered rapidly after release of the tourniquet, but was significantly lower (37 percent of baseline value, p<0.001) within two hours of reperfusion. In the ischaemia preconditioning group the microcirculation as in the ischaemia-reperfusion group recovered rapidly after release of the tourniquet, although failing to reach the baseline value within two hours of reperfusion. The mean microcirculation value of the left limb was slightly higher than Group 2 but significantly lower compared to the baseline after two hours of reperfusion (p<0.001). The change in the skeletal muscle microcirculation with cromakalim after two hours of reperfusion was not significant when compared to baseline values (p>0.05). The cromakalim group after two hours reperfusion had significantly higher microcirculation values when compared with Groups 2 and 3 (p<0.001). During ischaemia-reperfusion in Groups 2-4, there was no significant alteration in the systemic haemodynamic circulation. CONCLUSIONS: This study supports the hypothesis that cromakalim reduces postischaemic skeletal muscle damage and reperfusion injury.

Comparison of the inhibitory effects of cromakalim and pinacidil (potassium channel openers) with those of oxybutynin on stimulated guinea pig and rabbit detrusor muscle strips.

To compare the inhibitory effects of a new group of smooth muscle relaxants, the potassium channel openers cromakalim and pinacidil, with those of oxybutynin on detrusor muscle stimulation in animals. Detrusor strips of guinea pigs (n=16) and rabbits (n=20) were mounted in organ bath for recording of isometric tension. Alpha,beta-methylene ATP (10(-7), 10(-6), 10(-5) M), carbachol (10(-6), 10(-5), 3 x 10(-5), 5 x 10(-5) M) and transmural electrical-field stimulation (TES) were applied and concentration-response curves in the absence or presence of cromakalim (10(-6), 10(-5) M), pinacidil (10(-5), 5 x 10(-5) M) and oxybutynin (10(-5), 5 x 10(-5) M) were generated. All curves were displaced to the right in a concentration-dependent manner. The order of potency of inhibition was as follows: alpha,beta-methylene ATP (pinacidil>oxybutynin>cromakalim in guinea pigs; pinacidil>cromakalim>oxybutynin in rabbits); TES (pinacidil>cromakalim>oxybutynin in guinea pigs; cromakalim>oxybutynin>pinacidil in rabbits); carbachol (oxybutynin>pinacidil>cromakalim in guinea pigs; oxybutynin>cromakalim>pinacidil in rabbits). Cromakalim and pinacidil mainly inhibited purinergic-induced (alpha,beta-methylene ATP and TES) detrusor contractions.

Hemodynamic effects of levcromakalim in neonatal porcine pulmonary hypertension.

Levcromakalim (LKM; a K(ATP) channel opener) reverses hypoxic pulmonary vasoconstriction in isolated pulmonary arteries and perfused lungs. This vasorelaxation is blocked by glibenclamide (GLB; a K(ATP) channel blocker). We evaluated the hemodynamic effect of LKM followed by GLB in a chronically instrumented neonatal porcine model of pulmonary hypertension, created by exposing piglets to hypoxia (n = 7) or heat-killed group B streptococci (GBS) (n = 6). Hypoxia increased pulmonary arterial pressure (PAP), which LKM decreased, and GLB subsequently increased in a dose-dependent manner. Systemic arterial pressure (SAP) did not change with hypoxia but was also decreased by LKM and increased by GLB. GBS also led to increased PAP, but LKM significantly reduced only SAP, which was then increased by GLB. We conclude LKM is capable of reversing hypoxic, but not GBS-induced, pulmonary hypertension but lacks specificity for the neonatal pulmonary vasculature.

K(ATP) channel activation reduces the severity of postresuscitation myocardial dysfunction.

Postresuscitation myocardial dysfunction has been recognized as a leading cause of the high postresuscitation mortality rate. We investigated the effects of ischemic preconditioning and activation of ATP-sensitive K(+) (K(ATP)) channels on postresuscitation myocardial function. Ventricular fibrillation (VF) was induced in 25 Sprague-Dawley rats. Cardiopulmonary resuscitation (CPR), including mechanical ventilation and precordial compression, was initiated after 4 min of untreated VF. Defibrillation was attempted after 6 min of CPR. The animals were randomized to five groups treated with 1) ischemic preconditioning, 2) K(ATP) channel opener, 3) ischemic preconditioning with K(ATP) channel blocker administered 1 min after VF, 4) K(ATP) channel blocker administered 45 min before induction of ischemic preconditioning, and 5) placebo. Postresuscitation myocardial function, as measured by the rate of left ventricular pressure increase at 40 mmHg, the rate of left ventricular decline, cardiac index, and duration of survival, was significantly improved in both preconditioned and K(ATP) channel opener-treated animals. K(ATP) channel blocker administered 45 min before induction of ischemic preconditioning completely abolished the myocardial protective effects of preconditioning. We conclude that ischemic preconditioning significantly improved post-CPR myocardial function and survival. These results also provide evidence that the myocardial protective effects of ischemic preconditioning are mediated by K(ATP) channel activation.