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

Arteriolar oxygen reactivity: where is the sensor and what is the mechanism of action?

Arterioles in the peripheral microcirculation are exquisitely sensitive to changes in PO2 in their environment: increases in PO2 cause vasoconstriction while decreases in PO2 result in vasodilatation. However, the cell type that senses O2 (the O2 sensor) and the signalling pathway that couples changes in PO2 to changes in arteriolar tone (the mechanism of action) remain unclear. Many (but not all) ex vivo studies of isolated cannulated resistance arteries and large, first-order arterioles support the hypothesis that these vessels are intrinsically sensitive to PO2 with the smooth muscle, endothelial cells, or red blood cells serving as the O2 sensor. However, in situ studies testing these hypotheses in downstream arterioles have failed to find evidence of intrinsic O2 sensitivity, and instead have supported the idea that extravascular cells sense O2 . Similarly, ex vivo studies of isolated, cannulated resistance arteries and large first-order arterioles support the hypotheses that O2 -dependent inhibition of production of vasodilator cyclooxygenase products or O2 -dependent destruction of nitric oxide mediates O2 reactivity of these upstream vessels. In contrast, most in vivo studies of downstream arterioles have disproved these hypotheses and instead have provided evidence supporting the idea that O2 -dependent production of vasoconstrictors mediates arteriolar O2 reactivity, with significant regional heterogeneity in the specific vasoconstrictor involved. Oxygen-induced vasoconstriction may serve as a protective mechanism to reduce the oxidative burden to which a tissue is exposed, a process that is superimposed on top of the local mechanisms which regulate tissue blood flow to meet a tissue's metabolic demand.

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.

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.

Histamine induces MUC5AC expression via a hCLCA1 pathway

BACKGROUND

Histamine is an important inflammatory mediator and associated with early phase allergic response. However, the involvement of histamine in mucin gene expression or production has not been elucidated.

OBJECTIVE

The aim of this study is to investigate whether histamine induces MUC5AC production in NCI-H292 cells, and to evaluate which pathway is involved in this mucin production.

METHODS

MUC5AC production in NCI-H292 cells was analyzed by RT-PCR, immunoassay and immunocytochemical analysis. The effect of histamine on MUC5AC production in these cells at different time courses and concentrations was assessed, and the relationship between hCLCA1 expression and histamine concentration was also evaluated. In addition, cells were pretreated with antihistamine or an hCLCA1 blocker (niflumic acid, NFA) to evaluate the mechanism underlying histamine-induced MUC5AC production.

RESULTS

Histamine upregulated MUC5AC gene expression and mucin protein production in a dose-dependent and time-related fashion. Histamine also dose-dependently increased hCLCA1 mRNA expression. Moreover, pretreatment of cells with chlorpheniramine or NFA reduced histamine-induced MUC5AC mRNA expression and protein production in these cells. The histamine-treated cells showed increased cytoplasmic staining for MUC5AC compared to cells treated with media alone, and cells pretreated with chlorpheniramine or NFA before histamine treatment.

CONCLUSION

Our results suggest that histamine-induced MUC5AC production occurs via the upregulation of hCLCA1. It is assumed that antihistamines or hCLCA1 channel blockers can partially suppress histamine-induced MUC5AC production in allergic diseases, e.g. allergic rhinitis.

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.

The Cl(-) channel blocker niflumic acid releases Ca(2+) from an intracellular store in rat pulmonary artery smooth muscle cells

The effect of the Cl- channel blockers niflumic acid (NFA), 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), and anthracene-9-carboxylic acid (A-9-C), on Ca2+ signalling in rat pulmonary artery smooth muscle cells was examined. Intracellular Ca2+ concentration ([Ca2+]i) was monitored with either fura-2 or fluo-4, and caffeine was used to activate the ryanodine receptor, thereby releasing Ca2+ from the sarcoplasmic reticulum (SR). NFA and NPPB significantly increased basal [Ca2+]i and attenuated the caffeine-induced increase in [Ca2+]i. These Cl- channel blockers also increased the half-time (t1/2) to peak for the caffeine-induced [Ca2+]i transient, and slowed the removal of Ca2+ from the cytosol following application of caffeine. Since DIDS and A-9-C were found to adversely affect fura-2 fluorescence, fluo-4 was used to monitor intracellular Ca2+ in studies involving these Cl- channel blockers. Both DIDS and A-9-C increased basal fluo-4 fluorescence, indicating an increase in intracellular Ca2+, and while DIDS had no significant effect on the t1/2 to peak for the caffeine-induced Ca2+ transient, it was significantly increased by A-9-C. In the absence of extracellular Ca2+, NFA significantly increased basal [Ca2+]i, suggesting that the release of Ca2+ from an intracellular store was responsible for the observed effect. Depleting the SR with the combination of caffeine and cyclopiazonic acid prevented the increase in basal [Ca2+]i induced by NFA. Additionally, incubating the cells with ryanodine also prevented the increase in basal [Ca2+]i induced by NFA. These data show that Cl- channel blockers have marked effects on Ca2+ signalling in pulmonary artery smooth muscle cells. Furthermore, examination of the NFA-induced increase in [Ca2+]i indicates that it is likely due to Ca2+ release from an intracellular store, most probably the SR.

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 Cl- current in endothelin-1-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- channels in endothelin-1 (ET-1)-induced contraction in rabbit basilar artery. Male New Zealand White rabbits (n = 26), weighing 1.8-2.5 kg, were euthanized by an overdose of pentobarbital. The basilar arteries were removed for isometric tension recording. ET-1 produced a concentration-dependent contraction of the rabbit basilar artery in the normal Cl- Krebs-Henseleit bicarbonate buffer (123 mM Cl-). The ET-1-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 solution to disable Cl-/HCO exchanger, and 3) preincubation of rings with the Cl- channel blockers niflumic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid, and indanyloxyacetic acid 94. The ET-1-induced contraction was enhanced by substitution of extracellular Cl- (10 mM) with methanesulfonic acid (113 mM). Cl- channels are involved in ET-1-induced contraction in the rabbit basilar artery.

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

The role of membrane depolarization in the histamine-induced contraction of the rabbit middle cerebral artery was examined by simultaneous measurements of membrane potential and isometric force. Histamine (1-100 microM) induced a concentration-dependent sustained contraction associated with sustained depolarization. Action potentials were observed during depolarization caused by histamine but not by high-K(+) solution. K(+)-induced contraction was much smaller than sustained contraction associated with the same depolarization caused by histamine. Nifedipine attenuates histamine-induced sustained contraction by 80%, with no effect on depolarization. Inhibition of nonselective cation channels with Co(2+) (100-200 microM) reversed the histamine-induced depolarization and relaxed the arteries but induced only a minor change in K(+)-induced contraction. In the presence of Co(2+) and in low-Na(+) solution, histamine-evoked depolarization and contraction were transient. We conclude that nonselective cation channels contribute to histamine-induced sustained depolarization, which stimulates Ca(2+) influx through voltage-dependent Ca(2+) channels participating in contraction. The histamine-induced depolarization, although an important and necessary mechanism, cannot fully account for sustained contraction, which may be due in part to augmentation of currents through voltage-dependent Ca(2+) channels and Ca(2+) sensitization of the contractile process.