Histamine-induced depolarization: ionic mechanisms and role in sustained contraction of rabbit cerebral arteries

Function and Role of Histamine H1 Receptor in the Mammalian Heart

Histamine can change the force of cardiac contraction and alter the beating rate in mammals, including humans. However, striking species and regional differences have been observed. Depending on the species and the cardiac region (atrium versus ventricle) studied, the contractile, chronotropic, dromotropic, and bathmotropic effects of histamine vary. Histamine is present and is produced in the mammalian heart. Thus, histamine may exert autocrine or paracrine effects in the mammalian heart. Histamine uses at least four heptahelical receptors: H1, H2, H3 and H4. Depending on the species and region studied, cardiomyocytes express only histamine H1 or only histamine H2 receptors or both. These receptors are not necessarily functional concerning contractility. We have considerable knowledge of the cardiac expression and function of histamine H2 receptors. In contrast, we have a poor understanding of the cardiac role of the histamine H1 receptor. Therefore, we address the structure, signal transduction, and expressional regulation of the histamine H1 receptor with an eye on its cardiac role. We point out signal transduction and the role of the histamine H1 receptor in various animal species. This review aims to identify gaps in our knowledge of cardiac histamine H1 receptors. We highlight where the published research shows disagreements and requires a new approach. Moreover, we show that diseases alter the expression and functional effects of histamine H1 receptors in the heart. We found that antidepressive drugs and neuroleptic drugs might act as antagonists of cardiac histamine H1 receptors, and believe that histamine H1 receptors in the heart might be attractive targets for drug therapy. The authors believe that a better understanding of the role of histamine H1 receptors in the human heart might be clinically relevant for improving drug therapy.

UV-B Filter Octylmethoxycinnamate Is a Modulator of the Serotonin and Histamine Receptors in Human Umbilical Arteries

Every day, people use personal care products containing UV filters. Although their use initially showed a protective role, toxicity is a concern for human health as several UV filters are endocrine-disrupting chemicals (EDCs). Exposure to EDCs may induce cardiovascular diseases and can affect the health of sensitive people, such as pregnant women. Currently, the world’s most widely used UV-B filter is octylmethoxycinnamate (OMC), an EDC. However, the disruptive effects on pregnant women are little known. The present work proposed to understand how long-term exposure to OMC affects vascular homeostasis. Endothelium-denuded human umbilical artery (HUA) rings were incubated in an organ bath system. Long-term effects of exposure to OMC (0.001–50 μmol/L) were evaluated on the contractile responses of HUA to the application of the contractile agents, serotonin (5-HT) and histamine (Hist). To investigate in more detail the vascular mode of action of OMC, through which it impairs the vascular homeostasis of HUA, the activity and expression of different 5-HT and Hist-receptors involved in contractility processes were studied. Our findings pointed out an increase in the reactivity of HUA to 5-HT and Hist due to OMC exposure. These alterations in reactivity may be precursors of preeclampsia development and/or gestational hypertension.

UV-B Filter Octylmethoxycinnamate Alters the Vascular Contractility Patterns in Pregnant Women with Hypothyroidism

Increasing evidence relating the exposure and/or bioaccumulation of endocrine-disrupting compounds (EDCs) with cardiovascular system are arising. Octylmethoxycinnamate (OMC) is the most widely used UV-B filter and as EDC interacts with TH receptors. However, their effects on thyroid diseases during pregnancy remain unknown. The purpose of this work was to assess the short- and long-term effects of OMC on arterial tonus of pregnant women with hypothyroidism. To elucidate this, human umbilical artery (HUA) rings without endothelium were used to explore the vascular effects of OMC by arterial and cellular experiments. The binding energy and the modes of interaction of the OMC into the active center of the TSHR and THRα were analyzed by molecular docking studies. Our results indicated that OMC altered the contractility patterns of HUA contracted with serotonin, histamine and KCl, possibly due to an interference with serotonin and histamine receptors or an involvement of the Ca²⁺ channels. The molecular docking analysis show that OMC compete with T₃ for the binding center of THRα. Taken together, these findings pointed out to alterations in HUA reactivity as result of OMC-exposure, which may be involved in the development and increased risk of cardiovascular diseases.

Cl⁻ channels in smooth muscle cells

In smooth muscle cells (SMCs), the intracellular chloride ion (Cl−) concentration is high due to accumulation by Cl−/HCO3− exchange and Na+–K+–Cl− cotransportation. The equilibrium potential for Cl− (ECl) is more positive than physiological membrane potentials (Em), with Cl− efflux inducing membrane depolarization. Early studies used electrophysiology and nonspecific antagonists to study the physiological relevance of Cl− channels in SMCs. More recent reports have incorporated molecular biological approaches to identify and determine the functional significance of several different Cl− channels. Both "classic" and cGMP-dependent calcium (Ca2+)-activated (ClCa) channels and volume-sensitive Cl− channels are present, with TMEM16A/ANO1, bestrophins, and ClC-3, respectively, proposed as molecular candidates for these channels. The cystic fibrosis transmembrane conductance regulator (CFTR) has also been described in SMCs. This review will focus on discussing recent progress made in identifying each of these Cl− channels in SMCs, their physiological functions, and contribution to diseases that modify contraction, apoptosis, and cell proliferation.

H2 Receptor-Mediated Relaxation of Circular Smooth Muscle in Human Gastric Corpus: the Role of Nitric Oxide (NO)

This study was designed to examine the effects of histamine on gastric motility and its specific receptor in the circular smooth muscle of the human gastric corpus. Histamine mainly produced tonic relaxation in a concentration-dependent and reversible manner, although histamine enhanced contractility in a minor portion of tissues tested. Histamine-induced tonic relaxation was nerve-insensitive because pretreatment with nerve blockers cocktail (NBC) did not inhibit relaxation. Additionally, K⁺ channel blockers, such as tetraethylammonium (TEA), apamin (APA), and glibenclamide (Glib), had no effect. However, N^G-nitro-L-arginine methyl ester (L-NAME) and 1H-(1,2,4)oxadiazolo (4,3-A) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase (sGC), did inhibit histamine-induced tonic relaxation. In particular, histamine-induced tonic relaxation was converted to tonic contraction by pretreatment with L-NAME. Ranitidine, the H₂ receptor blocker, inhibited histamine-induced tonic relaxation. These findings suggest that histamine produced relaxation in circular smooth muscle of human gastric smooth muscle through H₂ receptor and NO/sGC pathways.

Beta adrenergic overstimulation impaired vascular contractility via actin-cytoskeleton disorganization in rabbit cerebral artery

Background and Purpose

Beta adrenergic overstimulation may increase the vascular damage and stroke. However, the underlying mechanisms of beta adrenergic overstimulation in cerebrovascular dysfunctions are not well known. We investigated the possible cerebrovascular dysfunction response to isoproterenol induced beta-adrenergic overstimulation (ISO) in rabbit cerebral arteries (CAs).

Methods

ISO was induced in six weeks aged male New Zealand white rabbit (0.8–1.0 kg) by 7-days isoproterenol injection (300 μg/kg/day). We investigated the alteration of protein expression in ISO treated CAs using 2DE proteomics and western blot analysis. Systemic properties of 2DE proteomics result were analyzed using bioinformatics software. ROS generation and following DNA damage were assessed to evaluate deteriorative effect of ISO on CAs. Intracellular Ca²⁺ level change and vascular contractile response to vasoactive drug, angiotensin II (Ang II), were assessed to evaluate functional alteration of ISO treated CAs. Ang II-induced ROS generation was assessed to evaluated involvement of ROS generation in CA contractility.

Results

Proteomic analysis revealed remarkably decreased expression of cytoskeleton organizing proteins (e.g. actin related protein 1A and 2, α-actin, capping protein Z beta, and vimentin) and anti-oxidative stress proteins (e.g. heat shock protein 9A and stress-induced-phosphoprotein 1) in ISO-CAs. As a cause of dysregulation of actin-cytoskeleton organization, we found decreased level of RhoA and ROCK1, which are major regulators of actin-cytoskeleton organization. As functional consequences of proteomic alteration, we found the decreased transient Ca²⁺ efflux and constriction response to angiotensin II and high K⁺ in ISO-CAs. ISO also increased basal ROS generation and induced oxidative damage in CA; however, it decreased the Ang II-induced ROS generation rate. These results indicate that ISO disrupted actin cytoskeleton proteome network through down-regulation of RhoA/ROCK1 proteins and increased oxidative damage, which consequently led to contractile dysfunction in CA.

Effect of histamine on regional cerebral blood flow of the parietal lobe in rats

Histamine is a powerful modulator that regulates blood vessels and blood flow. The effect of histamine on the extracortical vessels has been well described, while much less is known about the effect of histamine on intracortical vessels. In this study, we investigated the effect of histamine on regional cerebral blood flow in rat parietal lobe with laser Doppler flowmetry. The pharmacological characteristics of distinct ways (intracerebroventricular injection, intraperitoneal injection, and cranial window infusion) in applying histamine to the brain were also obtained and compared. Histamine applied in three ways all produced a decrease of rCBF in parietal lobe in a concentration-dependent manner. Cranial window infusion was the most effective way and intraperitoneal injection of L-histidine was the most ineffective, although it is a simple and applied way. To determine which type of receptor takes part in the vessel contraction induced by histamine, H1 receptor antagonist, diphenhydramine, and H2 receptor antagonist, cimetidine, were applied, respectively, before histamine administration. When the injection of cimetidine was conducted in advance, histamine still resulted in a decrease of infusion amount; while the injection of diphenhydramine was conducted in advance, the infusion of blood amount wasn't changed. These findings indicated that histamine could result in a reduction of rCBF in the rat parietal lobe and this effect of histamine may attribute partly to its combination with H1 receptor.

Metabotropic Ca(2+) channel-induced Ca(2+) release and ATP-dependent facilitation of arterial myocyte contraction

Voltage-gated Ca(2+) channels in arterial myocytes can mediate Ca(2+) release from the sarcoplasmic reticulum and, thus, induce contraction without the need of extracellular Ca(2+) influx. This metabotropic action of Ca(2+) channels (denoted as calcium-channel-induced calcium release or CCICR) involves activation of G proteins and the phospholipase C-inositol 1,4,5-trisphosphate pathway. Here, we show a form of vascular tone regulation by extracellular ATP that depends on the modulation of CCICR. In isolated arterial myocytes, ATP produced facilitation of Ca(2+)-channel activation and, subsequently, a strong potentiation of CCICR. The facilitation of L-type channel still occurred after full blockade of purinergic receptors and inhibition of G proteins with GDPbetaS, thus suggesting that ATP directly interacts with Ca(2+) channels. The effects of ATP appear to be highly selective, because they were not mimicked by other nucleotides (ADP or UTP) or vasoactive agents, such as norepinephrine, acetylcholine, or endothelin-1. We have also shown that CCICR can trigger arterial cerebral vasoconstriction in the absence of extracellular calcium and that this phenomenon is greatly facilitated by extracellular ATP. Although, at low concentrations, ATP does not induce arterial contraction per se, this agent markedly potentiates contractility of partially depolarized or primed arteries. Hence, the metabotropic action of L-type Ca(2+) channels could have a high impact on vascular pathophysiology, because, even in the absence of Ca(2+) channel opening, it might mediate elevations of cytosolic Ca(2+) and contraction in partially depolarized vascular smooth muscle cells exposed to small concentrations of agonists.

Pharmacology of the mouse-isolated cerebral artery

The routine availability of murine models of various cerebral circulatory disorders requires characterization of the regulation of cerebral artery tone in the mouse. Using vasoconstrictors and vasodilators with known efficacy in the cranial circulation of other species, we determined the pharmacological properties of the isolated pressurized mouse middle cerebral artery (MCA). The maximal pressure-induced myogenic constriction in isolated mouse MCA was 20.6+/-2.4%. Inhibition of nitric oxide (NO) and endothelin-1 (ET-1) altered the extent of pressure-induced myogenic tone. Isolated mouse MCA failed to either constrict or relax to 5-hydroxytryptamine (5-HT) and histamine; other vasoconstrictors demonstrated the following rank order of efficacy: ET-1>phenylephrine>U-46619. The rank order of endothelium-dependent vasodilator efficacy was bradykinin (BK)>acetylcholine (ACh)>substance P. The constriction produced by phenylephrine (PE) required a smaller increase in intracellular Ca(2+) elevation compared to constriction of a similar magnitude produced by membrane depolarization with potassium chloride (KCl). Pressure-induced myogenic tone (20-80 mm Hg) in mouse MCA was associated with smooth muscle cell membrane depolarization (-52.6+/-0.9 to -37.3+/-1.75 mV). Pressure-induced myogenic tone occurred with a smaller change in membrane potential compared to tone of a similar magnitude produced with KCl (-43.37+/-2.66 vs. -29.47+/-1.05 mV). The mouse MCA has a pharmacological profile that is distinct from other species including humans; however, similar to findings in other cerebral arteries, the mouse MCA shows intracellular sensitization to Ca(2+) following receptor activation.

TRPC3 mediates pyrimidine receptor-induced depolarization of cerebral arteries

We tested the hypothesis that TRPC3, a member of the canonical transient receptor potential (TRP) family of channels, mediates agonist-induced depolarization of arterial smooth muscle cells (SMCs). In support of this hypothesis, we observed that suppression of arterial SMC TRPC3 expression with antisense oligodeoxynucleotides significantly decreased the depolarization and constriction of intact cerebral arteries in response to UTP. In contrast, depolarization and contraction of SMCs induced by increased intravascular pressure, i.e., myogenic responses, were not altered by TRPC3 suppression. Interestingly, UTP-evoked responses were not affected by suppression of a related TRP channel, TRPC6, which was previously found to be involved in myogenic depolarization and vasoconstriction. In patch-clamp experiments, UTP activated a whole cell current that was greatly reduced or absent in TRPC3 antisense-treated SMCs. These results indicate that TRPC3 mediates UTP-induced depolarization of arterial SMCs and that TRPC3 and TRPC6 may be differentially regulated by receptor activation and mechanical stimulation, respectively.

Effects of pH on vascular tone in rabbit basilar arteries

Effects of pH on vascular tone and L-type Ca2+ channels were investigated using Mulvany myograph and voltage-clamp technique in rabbit basilar arteries. In rabbit basilar arteries, high K+ produced tonic contractions by 11+/-0.6 mN (mean+/-S.E.,n=19). When extracellular pH (pHo) was changed from control 7.4 to 7.9 ([alkalosis]o), K+-induced contraction was increased to 128+/-2.1% of the control (n=13). However, K+-induced contraction was decreased to 73+/-1.3% of the control at pHo 6.8 ([acidosis] o, n=4). Histamine (10 microM) also produced tonic contraction by 11+/-0.6 mN (n=17), which was blocked by post-application of nicardipine (1 microM). [alkalosis]o and [acidosis]o increased or decreased histamine-induced contraction to 134+/-5.7% and 27+/-7.6% of the control (n=4, 6). Since high K+- and histamine-induced tonic contractions were affected by nicardipine and pHo, the effect of pHo on voltage-dependent L-type Ca2+ channel (VDCCL) was studied. VDCCL was modulated by pHo: the peak value of Ca2+ channel current (IBa) at a holding of 0 mV decreased in [acidosis]o by 41+/-8.8%, whereas that increased in [alkalosis]o by 35+/-2.1% (n=3). These results suggested that the external pH regulates vascular tone partly via the modulation of VDCC in rabbit basilar arteries.

Manipulation of chloride flux affects histamine-induced contraction in rabbit basilar artery

Cl(-) efflux induces depolarization and contraction of smooth muscle cells. This study was undertaken to explore the role of Cl(-) flux in histamine-induced contraction in the rabbit basilar artery. Male New Zealand White rabbits (n = 16) weighing 1.8-2.5 kg were euthanized by an overdose of pentobarbital sodium. The basilar arteries were removed for isometric tension recording. Histamine produced a concentration-dependent contraction that was attenuated by the H(1) receptor antagonist chlorpheniramine (10(-8) M) but not by the H(2) receptor antagonist cimetidine (3 x 10(-6) M) in normal Cl(-) Krebs-Henseleit bicarbonate solution (123 mM Cl(-)). The histamine-induced contraction was reduced by the following manipulations: 1) inhibition of Na(+)-K(+)-2Cl(-) cotransporter with bumetanide (3 x 10(-5) and 10(-4) M), 2) bicarbonate-free HEPES solution to disable Cl(-)/HCO exchanger, and 3) blockade of Cl(-) channels with the use of niflumic acid, 5-nitro-2-(3-phenylpropylamino) benzoic acid, and indoleacetic acid 94 R-(+)-methylindazone. In addition, substitution of extracellular Cl(-) (10 mM) with methanesulfonate acid (113 mM) transiently enhanced histamine-induced contraction. Manipulation of Cl(-) flux affects histamine-induced contraction in the rabbit basilar artery.

Role of intracellular Ca(2+) release in histamine-induced depolarization in rabbit middle cerebral artery

The role of Ca(2+) mobilization from intracellular stores and Ca(2+)-activated Cl(-) channels in caffeine- and histamine-induced depolarization and contraction of the rabbit middle cerebral artery has been studied by recording membrane potential and isometric force. Caffeine induced a transient contraction and a transient followed by sustained depolarization. The transient depolarization was abolished by ryanodine, DIDS, and niflumic acid, suggesting involvement of Ca(2+)-activated Cl(-) channels. Histamine-evoked transient contraction in Ca(2+)-free solution was abolished by ryanodine or by caffeine-induced depletion of Ca(2+) stores. Ryanodine slowed the development of depolarization induced by histamine in Ca(2+)-containing solution but did not affect its magnitude. In arteries treated with 1 mM Co(2+), histamine elicited a transient depolarization and contraction, which was abolished by ryanodine. DIDS and niflumic acid reduced histamine-evoked depolarization and contraction. Histamine caused a sustained depolarization and contraction in low-Cl(-) solution. These results suggest that Ca(2+) mobilization from ryanodine-sensitive stores is involved in histamine-induced initial, but not sustained, depolarization and contraction. Ca(2+)-activated Cl(-) channels contribute mainly to histamine-induced initial depolarization and less importantly to sustained depolarization, which is most likely dependent on activation of nonselective cation channels.