Pituitary adenylate cyclase activating peptides relax human pulmonary arteries by opening of KATP and KCa channels

KATP channels in cerebral hemodynamics: a systematic review of preclinical and clinical studies

Cumulative evidence suggests that ATP-sensitive potassium (KATP) channels act as a key regulator of cerebral blood flow (CBF). This implication seems to be complicated, since KATP channels are expressed in several vascular-related structures such as smooth muscle cells, endothelial cells and pericytes. In this systematic review, we searched PubMed and EMBASE for preclinical and clinical studies addressing the involvement of KATP channels in CBF regulation. A total of 216 studies were screened by title and abstract. Of these, 45 preclinical and 6 clinical studies were included. Preclinical data showed that KATP channel openers (KCOs) caused dilation of several cerebral arteries including pial arteries, the middle cerebral artery and basilar artery, and KATP channel inhibitor (KCI) glibenclamide, reversed the dilation. Glibenclamide affected neither the baseline CBF nor the baseline vascular tone. Endothelium removal from cerebral arterioles resulted in an impaired response to KCO/KCI. Clinical studies showed that KCOs dilated cerebral arteries and increased CBF, however, glibenclamide failed to attenuate these vascular changes. Endothelial KATP channels played a major role in CBF regulation. More studies investigating the role of KATP channels in CBF-related structures are needed to further elucidate their actual role in cerebral hemodynamics in humans. Systematic review registration: Prospero: CRD42023339278 (preclinical data) and CRD42022339152 (clinical data).

Ion Channel Disturbances in Migraine Headache: Exploring the Potential Role of the Kynurenine System in the Context of the Trigeminovascular System

Migraine is a primary headache disorder, which is an enormous burden to the healthcare system. While some aspects of the pathomechanism of migraines remain unknown, the most accepted theory is that activation and sensitization of the trigeminovascular system are essential during migraine attacks. In recent decades, it has been suggested that ion channels may be important participants in the pathogenesis of migraine. Numerous ion channels are expressed in the peripheral and central nervous systems, including the trigeminovascular system, affecting neuron excitability, synaptic energy homeostasis, inflammatory signaling, and pain sensation. Dysfunction of ion channels could result in neuronal excitability and peripheral or central sensitization. This narrative review covers the current understanding of the biological mechanisms leading to activation and sensitization of the trigeminovascular pain pathway, with a focus on recent findings on ion channel activation and modulation. Furthermore, we focus on the kynurenine pathway since this system contains kynurenic acid, which is an endogenous glutamate receptor antagonist substance, and it has a role in migraine pathophysiology.

Involvement of Potassium Channel Signalling in Migraine Pathophysiology

Migraine is a primary headache disorder ranked as the leading cause of years lived with disability among individuals younger than 50 years. The aetiology of migraine is complex and might involve several molecules of different signalling pathways. Emerging evidence implicates potassium channels, predominantly ATP-sensitive potassium (KATP) channels and large (big) calcium-sensitive potassium (BKCa) channels in migraine attack initiation. Basic neuroscience revealed that stimulation of potassium channels activated and sensitized trigeminovascular neurons. Clinical trials showed that administration of potassium channel openers caused headache and migraine attack associated with dilation of cephalic arteries. The present review highlights the molecular structure and physiological function of KATP and BKCa channels, presents recent insights into the role of potassium channels in migraine pathophysiology, and discusses possible complementary effects and interdependence of potassium channels in migraine attack initiation.

Effect of KATP channel blocker glibenclamide on PACAP38-induced headache and hemodynamic

OBJECTIVE

To determine whether glibenclamide, a non-selective adenosine 5'-triphosphate-sensitive K⁺ (K_ATP) channel blocker, attenuates pituitary adenylate cyclase-activating polypeptide-38 (PACAP38)-induced headache and vascular changes in healthy volunteers.

METHODS

In a double-blind, randomized, placebo controlled and crossover design, 22 healthy volunteers were assigned to receive an intravenous infusion of 10 picomole/kg/min pituitary adenylate cyclase-activating polypeptide-38 over 20 minutes followed by oral administration of 10 mg glibenclamide or placebo. The primary endpoint was the difference in incidence of headache (0-12 hours) between glibenclamide and placebo. The secondary endpoints were a difference in area under the curve for headache intensity scores, middle cerebral artery velocity (V_meanMCA), superficial temporal artery diameter, radial artery diameter, heart rate, mean arterial blood pressure and facial skin blood flow between the two study days.

RESULTS

Twenty participants completed the study. We found no difference in the incidence of pituitary adenylate cyclase-activating polypeptide-38-induced headache after glibenclamide (19/20, 95%) compared to placebo (18/20, 90%) (P = 0.698). The area under the curve for headache intensity, middle cerebral artery velocity, superficial temporal artery diameter, radial artery diameter, facial skin blood flow, heart rate and mean arterial blood pressure did not differ between pituitary adenylate cyclase-activating polypeptide-38-glibenclamide day compared to pituitary adenylate cyclase-activating polypeptide-38-placebo day (P > 0.05).

CONCLUSIONS

Posttreatment with 5'-triphosphate-sensitive K₊ channel inhibitor glibenclamide did not attenuate pituitary adenylate cyclase-activating polypeptide-38-induced headache and hemodynamic changes in healthy volunteers. We suggest that pituitary adenylate cyclase-activating polypeptide-38-triggered signaling pathway could be mediated by specific isoforms of sulfonylurea receptor subunits of 5'-triphosphate-sensitive K₊ channels and other types of potassium channels.

The vascular effect of glibenclamide: A systematic review

Objective:

To systematically review the vascular effects of glibenclamide.

Background:

Infusion of adenosine triphosphate (ATP)-sensitive potassium (KATP) channel opener (KCO) levcromakalim dilates cranial arteries and induces headache and migraine attacks. Recent data show that levcromakalim-induced vasodilation is associated with headache. Glibenclamide is a KATP channel blocker that may alter the vascular tone and thus has an impact on headache or migraine prevention.

Methods:

A search through PubMed was undertaken for studies investigating the vascular effects of glibenclamide in vitro as well as in vivo published until July 2019.

Results:

We identified 58 articles; 31 in vitro studies, 24 in vivo studies and 3 studies with both. The main findings were that glibenclamide inhibited levcromakalim-induced and other KCOs-induced vasodilation, while the basal vascular tone remained unchanged.

Conclusion:

Glibenclamide could inhibit vasodilation by KCOs, and further studies are needed to clarify the vascular effect of glibenclamide on human cranial arteries.

Effect of pituitary adenylate cyclase-activating polypeptide-27 on cerebral hemodynamics in healthy volunteers: A 3T MRI study

Pituitary adenylate cyclase-activating polypeptide (PACAP) has emerged as an important signaling peptide in migraine pathogenesis. Recently, we have shown that the less-abundant PACAP isoform, PACAP27, induced migraine and headache in patients equipotently to PACAP38. The present study examined the effect of PACAP27 on cerebral hemodynamics in healthy volunteers using high resolution magnetic resonance angiography (MRA). Eighteen healthy volunteers received infusion of PACAP27 (10 pmol/kg/min) or placebo over 20 min and were scanned repeatedly in fixed intervals for 5 h in a double-blind, randomized, placebo-controlled study. The circumference of extra-intracerebral arteries was measured and compared with PACAP38 data. We found significant dilation of middle meningeal artery (MMA) (p = 0.019), superficial temporal artery (p = 0.001) and external carotid artery (p = 0.039) after PACAP27 infusion compared to placebo. Whereas the middle cerebral artery (MCA) (p = 0.011) and internal carotid artery (ICA) (p_ICAcervical = 0.015, p_ICAcerebral = 0.019) were constricted. No effects on basilar artery (p = 0.708) and cavernous portion of ICA were found. Post hoc analyses revealed significant larger area under the curve for MMA after PACAP38 compared to PACAP27 (p = 0.033). We also found that PACAP27 induced headache in nine out of twelve (75%) volunteers and one (17%) after placebo. In conclusion, PACAP27 induced headache and dilated extracerebral arteries (>5 h) and slightly constricted MCA in healthy volunteers. Post hoc analysis of PACAP38 data compared with PACAP27 showed that PACAP isoforms dilates MMA with significantly different magnitude.

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.

Pituitary adenylate cyclase-activating polypeptide (PACAP) induces relaxations of peripheral and cerebral arteries, which are differentially impaired by aging

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a well-known neuropeptide, which also has vasomotor effects. However, little is known regarding its age-related and organ-specific vasomotor effects. We hypothesized that the vasomotor effects of PACAP depend on the tissue origin of the vessels and aging substantially modulates its actions. Thus, carotid (CA) and basilar arteries (BA) were isolated from young (2 months old), middle age (12 months old), and old (30 months old) rats. Their vasomotor responses were measured with an isometric myograph (DMT610M) in response to cumulative concentrations of PACAP1-38 (10(-9)-10(-6) M). PACAP1-38 induced (1) significantly greater concentration-dependent relaxations in CA compared to that of BA of young, middle age, and old rats; (2) relaxations of CA significantly decreased, whereas they did not change substantially in BA, as a function of age; (3) sodium nitroprusside (SNP)-induced relaxation did not change after PACAP1-38 administration in any conditions; and (4) inhibition of PAC1 receptors by selective PAC1 receptor blocker (PACAP6-38) completely diminished the responses to PACAP in all age groups of BA and CA. In conclusion, these findings suggest that PACAP1-38 has greater vasomotor effect in CA than that in BA, whereas aging has less effect on PACAP-induced relaxation of cerebral arteries and BA than that in peripheral arteries and CA suggesting that the relaxation to PACAP is maintained in cerebral arteries even in old age.

Pituitary adenylate cyclase activating polypeptide (PACAP) dilates cerebellar arteries through activation of large-conductance Ca(2+)-activated (BK) and ATP-sensitive (K ATP) K (+) channels

Pituitary adenylate cyclase activating polypeptide (PACAP) is a potent vasodilator of numerous vascular beds, including cerebral arteries. Although PACAP-induced cerebral artery dilation is suggested to be cyclic AMP (cAMP)-dependent, the downstream intracellular signaling pathways are still not fully understood. In this study, we examined the role of smooth muscle K(+) channels and hypothesized that PACAP-mediated increases in cAMP levels and protein kinase A (PKA) activity result in the coordinate activation of ATP-sensitive K(+) (KATP) and large-conductance Ca(2+)-activated K(+) (BK) channels for cerebral artery dilation. Using patch-clamp electrophysiology, we observed that PACAP enhanced whole-cell KATP channel activity and transient BK channel currents in freshly isolated rat cerebellar artery myocytes. The increased frequency of transient BK currents following PACAP treatment is indicative of increased intracellular Ca(2+) release events termed Ca(2+) sparks. Consistent with the electrophysiology data, the PACAP-induced vasodilations of cannulated cerebellar artery preparations were attenuated by approximately 50 % in the presence of glibenclamide (a KATP channel blocker) or paxilline (a BK channel blocker). Further, in the presence of both blockers, PACAP failed to cause vasodilation. In conclusion, our results indicate that PACAP causes cerebellar artery dilation through two mechanisms: (1) KATP channel activation and (2) enhanced BK channel activity, likely through increased Ca(2+) spark frequency.

Involvements of PHI-nitric oxide and PACAP-BK channel in the sustained relaxation of mouse gastric fundus

The roles of nitric oxide (NO) and K(+) channels in sustained relaxation induced by electrical field stimulation (EFS) in the presence of atropine and guanethidine were studied in circular muscle strips of mouse gastric fundus. In the wild-type mouse, N(G)-nitro-l-arginine (l-nitroarginine), a nitric oxide synthase inhibitor, significantly inhibited the sustained relaxation in addition to the rapid relaxation. The sustained relaxation in pituitary adenylate cyclase-activating peptide (PACAP)-knockout mouse, which was smaller than that of the wild-type mouse, was also inhibited by l-nitroarginine. l-Nitroarginine inhibited the relaxation induced by the peptide histidine isoleucine (PHI), but not that induced by PACAP. S-Nitroso-N-acetyl-dl-penicillamine (SNAP), a NO donor, -induced relaxation was not affected by PACAP(6-38). EFS-induced sustained relaxation was inhibited by iberiotoxin, a big conductance calcium-activated K(+) (BK) channel inhibitor, but not by apamin, a small conductance calcium-activated K(+) (SK) channel inhibitor, and glibenclamide, an ATP-sensitive K(+) channel inhibitor. The relaxation that remained after the iberiotoxin-treatment was significantly inhibited by l-nitroarginine. Iberiotoxin inhibited PACAP-induced relaxation, while it had no effect on both PHI- and SNAP-induced relaxation. Immunoreactivities to anti-BK channel and anti-PHI antibodies were found in the circular muscle and the myenteric plexus layers, respectively. These results suggest interplay between PHI and NO in the sustained relaxation of the mouse gastric fundus, and that BK channels are involved in the PACAP-component of the sustained relaxation.

Pulmonary and systemic effects of inhaled PACAP38 in healthy male subjects

BACKGROUND

Pituitary adenylate cyclase activating polypeptide 1-38 (PACAP38) displays biological activities (e.g. bronchodilatory, pulmonary vasodilatory and anti-inflammatory properties) that are relevant in several pulmonary diseases. The aim of this study was to assess the safety and tolerability and the pulmonary and systemic effects of inhaled PACAP38 in humans.

MATERIALS AND METHODS

Twelve healthy male subjects (mean age 28) were studied in a randomized, double-blind, placebo-controlled dose escalation trial with inhalation of PACAP38 to a cumulative dose of 480 microg. Lung function was measured by body plethysmography. Systemic absorption was evaluated by plasma levels, skin blood flux (estimated by laser Doppler imager fluxmetry) and systemic haemodynamics.

RESULTS

Inhalation of PACAP38 did not cause relevant adverse reactions or an increase of PACAP38 plasma levels. No statistically significant changes in lung function tests and no systemic effects (blood pressure, pulse rate or skin blood flux) occurred.

CONCLUSION

Inhaled PACAP38 was well tolerated without systemic side-effects in healthy male subjects.

Mediators and modulators of pulmonary arterial hypertension

Pulmonary hypertension (PH), defined as a mean pulmonary arterial (PA) pressure of >25 mmHg at rest or >30 mmHg during exercise, is characterized by a progressive and sustained increase in pulmonary vascular resistance that eventually leads to right ventricular failure. Clinically, PH may result from a variety of underlying diseases (Table 1 and Refs. 50, 113, 124). Pulmonary arterial hypertension (PAH) may be familial (FPAH) or sporadic (idiopathic, IPAH), formerly known as primary pulmonary hypertension, i.e., for which there is no demonstrable cause. More often, PAH is due to a variety of identifiable diseases including scleroderma and other collagen disorders, liver disease, human immunodeficiency virus, and the intake of appetite-suppressant drugs such as phentermine and fenfluramine (72). Other, more common, causes of PAH include left ventricular failure (perhaps the most common cause), valvular lesions, chronic pulmonary diseases, sleep-disordered breathing, and prolonged residence at high altitude. This classification, now widely accepted, was first proposed at a meeting in Evian, France, in 1998, and modified in Venice, Italy, in 2003 (124).

Effect of adenosine triphosphate-sensitive potassium channel openers on lung preservation

ATP-sensitive potassium channel (KATP) openers have been proven to be involved in ischemic preconditioning, which protects ischemic tissue. However, the effect of KATP openers on ischemia-reperfusion injury of the lungs remains unknown. We investigated whether a KATP opener, pinacidil, can attenuate ischemia-reperfusion injury using an ex vivo rat lung model. Heart-lung blocks were flushed and preserved with phosphate-buffered saline (control group) or with one of the solutions containing pinacidil (pinacidil group) or pinacidil + glibenclamide (a KATP blocker) (glibenclamide group). The control and glibenclamide groups showed significantly higher values with respect to shunt fraction, pulmonary arterial pressure, and peak inspiratory pressure than the pinacidil group. The concentrations of total adenine nucleotides and ATP in the lung after reperfusion became significantly lower in the control and glibenclamide groups than in the fresh group. Lipid peroxidation of the lungs increased significantly in the control and glibenclamide groups after reperfusion. State 3 mitochondrial respiration and State 3/4 ratios of mitochondrial respiration were significantly decreased in the lungs of the control and glibenclamide groups. These findings suggested that KATP openers would maintain the mitochondrial respiratory function during lung preservation, prevent lipid peroxidation after reperfusion, and attenuate ischemia-reperfusion injury.

Pituitary adenylate cyclase-activating polypeptide activates K(ATP) current in rat atrial myocytes

Because the electrophysiological effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on the heart are little known, we studied the regulation of the atrial ATP-sensitive K(+) (K(ATP)) current by PACAP on primary cultured neonatal rat atrial myocytes. PACAP-38 stimulates cAMP production with EC(50) = 0.28 nmol/l (r = 0.92, P < 0.02). PACAP-38 and PACAP-27 (10 nmol/l) have similar maximal effects, whereas 100 nmol/l vasoactive intestinal polypeptide (VIP) is 2.7 times less effective (P < 0.05). RT-PCR shows the presence of cloned PACAP receptors PAC(1) (> or =2 isoforms), VPAC(1), and VPAC(2). PACAP-38 dose dependently activates the whole cell atrial K(ATP) current with EC(50) = 1-3 nmol/l (n = 44). Maximal effects occur at 10 nmol/l (91 +/- 15 pA/pF, n = 18). Diazoxide further increases the PACAP-activated current by 78% (P < 0.05; n = 6). H(89) (500 nmol/l), a protein kinase A (PKA) inhibitor, reduces the PACAP-activated K(ATP) current to 17.8 +/- 9.6% (n = 5) of the maximal diazoxide-induced current and totally inhibits the cAMP-induced K(ATP) current. A protein kinase C (PKC) inhibitor peptide (50 micromol/l) in the pipette reduces the PACAP-38-induced K(ATP) current to 33 +/- 17 pA/pF (P < 0.05, n = 6) without significantly affecting the currents induced by cAMP or VIP. The results suggest that: 1) PAC(1), VPAC(1), and VPAC(2) are present in atrial myocytes; and 2) PACAP-38 activates the atrial K(ATP) channels through both PKA and PKC pathways.