The bradykinin receptor--a putative receptor-operated channel in PC12 cells: studies of neurotransmitter release and inositol phosphate accumulation

Translationally Controlled Tumor Protein Stimulates Dopamine Release from PC12 Cells via Ca2+-Independent Phospholipase A₂ Pathways

The translationally controlled tumor protein (TCTP), initially identified as a tumor- and growth-related protein, is also known as a histamine-releasing factor (HRF). TCTP is widely distributed in the neuronal systems, but its function is largely uncharacterized. Here, we report a novel function of TCTP in the neurotransmitter release from a neurosecretory, pheochromocytoma (PC12) cells. Treatment with recombinant TCTP (rTCTP) enhanced both basal and depolarization (50 mM KCl)-evoked [³H]dopamine release in concentration- and time-dependent manners. Interestingly, even though rTCTP induced the increase in intracellular calcium levels ([Ca²⁺]_i), the rTCTP-driven effect on dopamine release was mediated by a Ca²⁺-independent pathway, as evidenced by the fact that Ca²⁺-modulating agents such as Ca²⁺ chelators and a voltage-gated L-type Ca²⁺-channel blocker did not produce any changes in rTCTP-evoked dopamine release. In a study to investigate the involvement of phospholipase A₂ (PLA₂) in rTCTP-induced dopamine release, the inhibitor for Ca²⁺-independent PLA₂ (iPLA₂) produced a significant inhibitory effect on rTCTP-induced dopamine release, whereas this release was not significantly inhibited by Ca²⁺-dependent cytosolic PLA₂ (cPLA₂) and secretory PLA₂ (sPLA₂) inhibitors. We found that rTCTP-induced dopamine release from neuronal PC12 cells was modulated by a Ca²⁺-independent mechanism that involved PLA₂ in the process, suggesting the regulatory role of TCTP in the neuronal functions.

Mechanisms in bradykinin stimulated arachidonate release and synthesis of prostaglandin and platelet activating factor

Regulatory mechanisms in bradykinin (BK) activated release of arachidonate (ARA) and synthesis of prostaglandin (PG) and platelet activating factor (PAF) were studied in bovine pulmonary artery endothelial cells (BPAEC). A role for GTP binding protein (G-protein) in the binding of BK to the cells was determined. Guanosine 5-O- (thiotriphosphate), (GTPtauS), lowered the binding affinity for BK and increased the Kd for the binding from 0.45 to 1.99 nM. The Bmax remained unaltered at 2.25 x 10(-11) mole. Exposure of the cells to aluminium fluoride also reduced the affinity for BK. Bradykinin-induced release of ARA proved pertussis toxin (PTX) sensitive, with a maximum sensitivity at 10 ug/ml PTX. GTPtauS at 100 muM increased the release of arachidonate. The effect of GTPtauS and BK was additive at suboptimal doses of BK up to 0.5 nM but never exceeded the levels of maximal BK stimulation at 50 nM. PTX also inhibited the release of ARA induced by the calcium ionophore, A23187. Phorbol 12-myristate 13-acetate or more commonly known as tetradecanoyl phorbol acetate (TPA) itself had little effect on release by the intact cells. However, at 100 nM it augmented the BK activated release. This was downregulated by overnight exposure to TPA and correlated with down-regulation of protein kinase C (PKC) activity. The down-regulation only affected the augmentation of ARA release by TPA but not the original BK activated release. TPA displayed a similar, but more potent amplification of PAF synthesis in response to both BK or the calcium ionophore A23187. These results taken together point to the participation of G-protein in the binding of BK to BPAEC and its activation of ARA release. Possibly two types of G-protein are involved, one associated with the receptor, the other activated by Ca(2+) and perhaps associated with phospholipase A(2) (PLA(2)). Our results further suggest that a separate route of activation, probably also PLA(2) related, takes place through a PKC catalysed phosphorylation.

Alleviation of oxidative stress by potent and selective thioredoxin-mimetic peptides

One of the major enzymatic cell defenses providing protection from oxidative injury is the TrxR-Trx system. It consists of NADPH and thioredoxin reductase (TrxR), which maintain thioredoxin (Trx) in a reduced state. Perturbing the TrxR-Trx system with the selective TrxR inhibitor auranofin (AuF; 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato-S-(triethylphosphine) gold) induces oxidative stress by keeping Trx in its oxidized state. We have prepared a family of tri- and tetra-oligopeptides derived from the canonical CxxC motif of the Trx active site and a modified CxC motif. These Trx-mimetic compounds are N- and C-terminal-blocked peptides that consist of two cysteine residues that flank the two-amino-acid CxxC motif (CB4 and CB6) or the single-amino-acid CxC motif (CB3). Catecholamine (CA) secretion in bovine chromaffin cells, which is a highly redox sensitive process, is abolished by AuF. The Trx-mimetic peptides effectively restore CA secretion, as monitored by amperometry in single cells. They also prevent the AuF-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase. In PC12 cells, the alleviation of AuF-induced ERK1/2-MAPK phosphorylation by Trx-like peptides parallels their effect of restoring CA secretion. CB3, CB4, and CB6 act intracellularly and are significantly more potent than the traditional antioxidants NAC, GSH, DTT, AD4 (NAC-amide), and ascorbic acid. Taken together, the CxxC and CxC peptides represent a new family of potent and selective redox compounds that could serve as potential candidates for prevention and treatment of oxidative-stress-related disorders.

Nongenomic mechanism of glucocorticoid inhibition of bradykinin-induced calcium influx in PC12 cells: possible involvement of protein kinase C

Many stimulants, including bradykinin (BK), can induce increase in [Ca(2+)](i) in PC12 cells. Bradykinin induces an increase in [Ca(2+)](i) via intracellular Ca(2+) release and extracellular Ca(2+) influx through the transduction of G protein, but not through voltage-sensitive calcium channels. In this experiment, We analyzed how corticosterone (Cort) influences BK-induced intracellular Ca(2+) release and extracellular Ca(2+) influx, and further studied the mechanism of glucocorticoid's action. To dissociate the intracellular Ca(2+) release and extracellular Ca(2+) influx induced by BK, the Ca(2+)-free/Ca(2+)- reintroduction protocol was used. The results were as follows: (1) The Ca(2+) influx induced by BK could be rapidly inhibited by Cort, but intracellular Ca(2+) release could not be affected significantly. (2) The inhibitory effect of Cort-BSA (BSA -conjugated Cort) on Ca(2+) influx induced by BK was the same as the effect of free Cort. (3) Protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate) could mimic and PKC inhibitor Gö6976 could reverse the inhibitory effect of Cort. (4) There was no inhibitory effect of Cort on Ca(2+) influx induced by BK when pretreated with pertussis toxin. The results suggested, for the first time, that Cort might act via a putative membrane receptor and inhibit the Ca(2+) influx induced by BK through the pertussis toxin -sensitive G protein-PKC pathway.

Bradykinin-induced neuropeptide Y release by human pheochromocytoma tissue

Neuropeptide Y (NPY) and noradrenaline (NA) are frequently co-localized and co-released in the sympathetic nervous system. Since bradykinin (BK) is known to stimulate neurotransmitter release as NA in adrenal glands, we therefore hypothesized that BK might also be involved in the release of NPY. The effect of BK(1-9) on immunoreactive NPY (Ir-NPY) release was investigated in superfused human pheochromocytoma tissue. BK(1-9) (10(-7)-10(-5) M) was shown to induce a rapid Ir-NPY release in a concentration-dependent manner. This effect of BK(1-9) (10(-6) M) was mimicked by the B2 agonist [Phe(8)(CH(2)NH)Arg(9)]-bradykinin (10(-5) M) and blocked by the selective B2-receptor antagonist HOE140 (10(-5) M). Increasing Ir-NPY release was probably not mediated by nitric oxide (NO) since the outflow of Ir-NPY was not influenced by the NO synthase inhibitor N-omega-nitro-L-arginine methyl ester (L-NAME) (10(-4) M). In presence of bapta-AM (10(-5) M), a chelator of cytosolic calcium, W7 (10(-5) M), a calmodulin inhibitor, TMB-8 (10(-5) M), a blocker of intracellular calcium mobilization and ryanodine (10(-5) M), a selective inhibitor of the Ca(2+)-induced release mechanism, the NPY release by BK(1-9) was significantly inhibited by 126%, 98%, 91%, and 94%, respectively. These results indicate that BK increased the release of NPY by the tumor acting through the interaction with the BK-B2 receptor and request intracellular calcium mobilization independently of a NO mechanism.

Tunicamycin Dissociates Depolarization-induced Calcium Entry From Transmitter Release. Involvement of Glycosylated Protein(s) in the Process of Neurosecretion in PC-12 Cells

The process of regulated secretion in PC-12 cells is tightly coupled to calcium entry, which is absolutely dependent on extracellular Ca2+([Ca2+]ex). Tunicamycin treatment of the cells dissociated depolarization-triggered Ca2+ influx from depolarization (high K+)-induced transmitter release into two distinct and independent phases. Deplarization-evoked Ca2+ influx was not affected by tunicamycin treatment (1 microg/ml, 72 h), whereas depolarization-evoked transmitter release was strongly inhibited (> 60%), suggesting at least a two-step process, and the participation of glycosylated protein(s) in the actual fusion/secretion step. Similarly, bradykinin-mediated transmitter release was linearly related to and absolutely dependent on Ca2+ entry, and was inhibited by tunicamycin treatment (> 80%), whereas bradykinin-evoked Ca2+ entry was not impaired, indicating that glycosylated protein(s) are essential for bradykinin-evoked release at a step subsequent to Ca2+ influx. The heavily glycosylated alpha2 subunit of the dihydropyridine-sensitive channel, which was used to monitor tunicamycin inhibition of glycosylation, was not expressed in the tunicamycin-treated cells, as shown by Western blot analysis. This observation allowed us to conclude that the alpha1 subunit of the heteromeric dihydropyridine voltage-sensitive Ca2+ channel, which is responsible for Ca2+ entry, is also fully functional when not assembled with its corresponding alpha2 subunit. The molecular properties of the alpha2 subunit, whose role in the complex structure of the channel is not yet understood, are shown for the first time for the L-type Ca2+ channel of PC-12 cells. Similar to cardiac and skeletal muscle cells, the alpha2 subunit appears to be a glycosylated polypeptide of molecular weight 170 kD and to display a characteristic mobility shift to 140 kD under reducing conditions.

A two-cell biosensor that couples neuronal cells to optically monitored fish chromatophores

A two-cell biosensor was developed that uses optically detected changes in naturally colored fish chromatophores to measure the neurosecretory output of mammalian neuronal cells. The specific version of the biosensor described here is a continuous flow device that places red-pigmented, dendritic erythrophore cells directly downstream of an immobilized population of PC12 neuronal cells, a well-established model cell-line having neuroendocrine function. Agents known to stimulate catecholamine neurosecretion (secretagogues) were presented to the PC12 cells. It was found that the varying level of neurosecretion from the PC12 cells was measurable by judging the degree of pigment aggregation in the erythrophores. Increases in catecholamine secretion and consequent pigment aggregation were observed for several known secretagogues, including receptor agonists (ATP, acetylcholine), membrane depolarizing agents (high K(+) concentration), and specific neurotoxins (black widow spider venom, alpha-latrotoxin). This particular two-cell biosensor, which is applicable to the detection of any agents that affect the levels of catecholamine secretion from PC12 cells, demonstrates the general principle that the breadth of sensitivity of a biosensor is increased by employing coupled cell types.

Pleiotropic signaling pathways in rapid, nongenomic action of glucocorticoid

The traditional genomic theory of steroid action does not fully explain the rapid effects of hormonal steroids, and it is thought that the nongenomic actions mediated by a putative membrane receptor may provide a plausible explanation. Although there is a rich body of evidence to substantiate the rapid, nongenomic effects of steroid hormones, the signal transduction pathways involved have proved to be complex and pleiotropic. Based on previous studies on the rapid, nongenomic actions of glucocorticoid (GC) and the G-protein-protein kinase pathways involved, including our own studies on PC12, SK-N-SH, BT-325 cells, and synaptosomes, in this review we will discuss the issue of multiple signal transduction pathways involved in the rapid, nongenomic effects of GC.

Bradykinin B2-receptor activation augments norepinephrine exocytosis from cardiac sympathetic nerve endings. Mediation by autocrine/paracrine mechanisms

We determined whether local bradykinin production modulates cardiac adrenergic activity. Depolarization of guinea pig heart sympathetic nerve endings (synaptosomes) with 1 to 100 mmol/L K+ caused the release of endogenous norepinephrine (10% to 50% above basal level). This release was exocytotic, because it depended on extracellular Ca2+, was inhibited by the N-type Ca(2+)-channel blocker omega-conotoxin and the protein kinase C inhibitor Ro31-8220, and was potentiated by the neuronal uptake-1 inhibitor desipramine. Typical of adrenergic terminals, norepinephrine exocytosis was enhanced by activation of prejunctional angiotensin AT1-receptors and attenuated by adrenergic alpha 2-receptors, adenosine A1-receptors, and histamine H3-receptors. Exogenous bradykinin enhanced norepinephrine exocytosis by 7% to 35% (EC50, 17 nmol/L), without inhibiting uptake 1. B2-receptor, but not B1-receptor, blockade antagonized this effect. The kininase II/angiotensin-converting enzyme inhibitor enalaprilat and the addition of kininogen or kallikrein enhanced norepinephrine exocytosis by approximately equal to 6% to 40% (EC50, 20 nmol/L) and approximately equal to 25% to 60%, respectively. This potentiation was prevented by serine protease inhibitors and was antagonized by B2-receptor blockade. Therefore, norepinephrine exocytosis is augmented when bradykinin synthesis is increased or when its breakdown is inhibited. This is the first report of a local kallikrein-kinin system in adrenergic nerve endings capable of generating enough bradykinin to activate B2-receptors in an autocrine/paracrine fashion and thus enhance norepinephrine exocytosis. This amplification process may operate in disease states, such as myocardial ischemia, associated with severalfold increases in local kinin concentrations.

Autoradiographic localization and characterization of bradykinin receptors in human skin

High affinity [3H]bradykinin binding sites have been identified in human skin cryosections by in vitro autoradiography. Equilibrium binding studies were performed with increasing concentrations of [3H]bradykinin for 120 min in the presence of protease inhibitors at 4 degrees C. In saturation experiments a single class of high affinity binding sites was identified with a dissociation constant Kd of 1.2 +/- 0.8 nM (mean +/- S.E.M., n = 3) and a maximal binding capacity Bmax of 33 +/- 8 fmol [3H]bradykinin specifically bound/mg protein (mean +/- S.E.M., n = 3). Competition experiments revealed a rank order of potency with bradykinin being most effective (bradykinin = [Lys]bradykinin > [Met- Lys]bradykinin > [Tyr]bradykinin > [des-Arg9]bradykinin), whereas [des-Arg9]bradykinin was ineffective. This indicates a B2 subtype of bradykinin receptors in normal human skin. Morphological data: autoradiography revealed that bradykinin receptors were localized in the stratum basale of the epidermis. The data are consistent with the hypothesis, that these mitotic active keratinocytes express bradykinin binding sites, that fulfil the pharmacological criteria for true receptors. Diverse stimuli, including bradykinin, play a role in the mediation of cutaneous inflammatory responses (e.g. fluid extravasation, reactive cell proliferation, hyperalgesia). Our data indicate that specific kinin receptors of the stratum basale are likely to contribute to these effects.

ATP receptor-mediated increase of Ca ionophore-stimulated arachidonic acid release from PC12 pheochromocytoma cells

Phospholipase A2 has recently been proposed as the effector enzyme involved in the receptor-mediated release of arachidonic acid (AA). Released AA and its metabolites have been demonstrated to play an important role in the regulation of cell functions. [3H]AA release from prelabeled PC12 cells was stimulated by a Ca ionophore such as ionomycin or A23187. Although ATP and its effective analog, adenosine 5'-O-(3-thiotrisphosphate) (ATP gamma S), 2-methylthio ATP and 3'-O-(4-benzoyl)benzoyl ATP, did not stimulate [3H]AA release on their own, they did enhance Ca ionophore-stimulated [3H]AA release. The effect of ATP analogs was dose-dependent. ADP, UTP, GTP, ITP, alpha beta-methylene ATP, beta gamma-methylene ATP and 8-bromo ATP showed no effect or very limited effect. The effect of ATP gamma S was antagonized by suramin, a putative P2Y receptor antagonist. The effective ATP analogs also increased [Ca2+]i (cytosolic free Ca2+ concentration) via Ca2+ influx. However, the addition of 50 mM KCl or 10 microM bradykinin, which are well-known to increase [Ca2+]i by different pathways, did not stimulate [3H]AA release, either with or without the Ca ionophore. The addition of phorbol 12-myristate 13-acetate, an activator of protein kinase C, showed no effect on [3H]AA release, either with or without the Ca ionophore. These data suggest that 1) ATP increased Ca ionophore-stimulated AA release via a P2Y-like ATP receptor, and that 2) the elevation of [Ca2+]i by ATP does not quantitatively explain the ATP-stimulated AA release in PC12 cells.

Purine and pyrimidine nucleotides activate distinct signalling pathways in PC12 cells

The role of extracellular nucleotides in intracellular signalling and neurosecretion was assessed in PC12 cells. Activation of phospholipase C and increased [Ca2+]i were mediated by purinoceptors with an agonist potency profile, ATP approximately UTP > 2-methylthioadenosine triphosphate (2-MeSATP), typical of P2U. ATP also evoked a rapid acidification followed by a more gradual alkalinization (measured with 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF)), while UTP induced only a gradual alkalinization. The amiloride analogue 5-(N-ethyl-N-isopropyl)amiloride (EIPA) attenuated the alkalinization phase suggesting activation of the Na+/H+ exchanger by ATP and UTP. Using bisoxonol and [3H]tetraphenylphosphonium ([3H]TPP+) as potential-sensitive probes, we showed that while ATP rapidly depolarized PC12 cells in an Na(+)-dependent manner, UTP evoked a much reduced and delayed response. The potency profile (ATP approximately 2-MeSATP approximately adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) >> UTP, alpha, beta-methyleneATP) suggested involvement of a receptor subtype distinct from P2U. Secretion of endogenous dopamine was also assessed. Those nucleotides that induced depolarization (ATP, 2-MeSATP, ATP gamma S) were also the most potent secretagogues. UTP was ineffective. Our results suggest that ATP stimulates distinct purinoceptor subtypes and induces neurosecretion through the activation of multiple signalling pathways.

Regulatory mechanisms involved in the activation of bradykinin-induced membrane currents in PC12 cells

Whole-cell patch-clamp measurements were made in nerve-growth-factor (NGF)-treated PC12 cells. External application of bradykinin (BK) activated an outward and an inward current which could be separated by using KCl- or CsCl-containing pipette solutions. The slowly activating inward current could be induced by BK independently of the filling of intracellular Ca2+ stores. By using GDP-beta-S in the pipette medium, we showed that BK-induced outward and inward currents were differentially regulated through G-protein-sensitive and -insensitive mechanisms, respectively. While the outward current was inhibited by GDP-beta-S, the inward current was not affected. Our results show that occupancy of BK receptors activates different signaling pathways for the induction of outward and inward currents.

Bradykinin-evoked release of [3H]noradrenaline from the human neuroblastoma SH-SY5Y

Bradykinin (BK) evoked [3H]noradrenaline ([3H]NA) release from the human neuroblastoma SH-SY5Y and this was enhanced by pre-treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) for 8 min. This effect of BK was inhibited by 500 microM [D-Phe7]BK and 100 microM [Thi5,8,D-Phe7]BK but not by 500 microM [Des-Arg9,Leu8]BK. The BK (B1)-agonist [Des-Arg9]BK did not evoke [3H]NA release. This suggested that SH-SY5Y expressed BK (B2)-receptors coupled to the release of [3H]NA. BK acting at B2-receptors, also elevated intracellular calcium and depolarized SH-SY5Y cells. Although pre-treatment of SH-SY5Y cells with TPA enhanced BK-evoked [3H]NA release, the elevation of intracellular calcium [Ca2+]; was decreased by about 50%. BK-evoked release of [3H]NA in cells not pre-treated with phorbol ester was only 23% dependent on extracellular calcium. In comparison, following phorbol ester treatment approximately 40% of [3H]NA release was dependent on extracellular calcium. Nifedipine (5 microM), CoCl2 (1 mM) and NiCl2 (1 mM) inhibited NA release in SH-SY5Y cells pre-treated with TPA by 16.0, 47 and 44%, respectively. The results of this study showed that BK, acting at B2-receptors, activated [3H]NA release in SH-SY5Y. Part of this effect appeared to be due to activation of L-type calcium channels but the majority of BK-evoked [3H]NA release in SH-SY5Y cells appeared to depend on [Ca2+]i.

Cardiac L-type Ca2+ channel triggers transmitter release in PC12 cells

Among the various voltage-sensitive Ca2+ channels present in PC12 cells are the dihydropyridine (DHP)-sensitive L-channel, the omega-conotoxin (omega-CgTx)-sensitive N-channel, and an atypical omega-CgTx/DHP-insensitive Ca2+ channel. Depolarization-evoked Ca2+ entry and [3H]dopamine release is mediated by L-type Ca2+ channels determined by the use of Ca2+ channel antagonists, and a single protein of 250 kDa is recognized by L-type-specific antibodies. Screening of a PC12 cDNA library revealed two types of Ca2+ channels which were identified by partial sequencing. A pc12-L clone displayed virtually identical sequence homology to the cardiac L-type channel. The identical sequence homology of the single alternative splicing region confirmed clone pc12-L as the rbC-I transcript, a cardiac-neuronal alpha 1 subunit expressed in rat brain. Clone pc12-N displayed identical sequence homology to rbB-I, a neuronal alpha 1 subunit of the N-type Ca2+ channel expressed in rat brain; Northern blot analysis identified RNA of a size similar to that previously described for rat brain.

Inhibition by ethaverine of catecholamine secretion through blocking L-type Ca2+ channels in PC12 cells

Ethaverine, a derivative of papaverine, is used as a vasodilator and antispasmodic drug. We have investigated the effects of ethaverine on the secretion of [3H]norepinephrine from PC12 cells, of neuroendocrine origin. Treatment with ethaverine reduced catecholamine secretion in a concentration-dependent manner. The maximal inhibitory effect (90%) was achieved with 10 microM ethaverine, and the IC50 for secretion was approximately 2 microM. Ethaverine pretreatment for 1 min prior to stimulation by 70 mM K+ also decreased the level of intracellular Ca2+ in a concentration-dependent manner, as measured by fura-2 fluorescence. The IC50 for the inhibition of the increase in intracellular Ca2+ was approximately 2 microM. Nifedipine, a dihydropyridine L-type Ca2+ channel blocker, did not enhance the inhibitory effect of ethaverine on the 70 mM K(+)-induced increase in [Ca2+]i or catecholamine secretion. In contrast, the addition of the N-type voltage-sensitive Ca2+ channel antagonist omega-conotoxin with ethaverine resulted in further reductions in the increase in [Ca2+]i and catecholamine release. Maximally effective concentrations of ethaverine and nifedipine showed the same inhibitory effect on the 70 mM K(+)-evoked responses. However, ethaverine pretreatment did not inhibit the bradykinin-induced secretion and [Ca2+]i rise, which are known to be produced through the receptor-operated Ca2+ channels. We conclude that ethaverine reduces catecholamine secretion by blocking the L-type voltage-sensitive Ca2+ channel.

Caffeine-induced transmitter release is mediated via ryanodine-sensitive channel

An isolated clone PC12-37 of rat pheochromocytoma PC12 cells, which lacks ryanodine-sensitive Ca2+ channel, responds to depolarization and to agonist activation and triggers [3H]dopamine ([3H]DA) release. A caffeine-stimulated transmitter release, while present in the parental PC12 cell line, is completely abolished in PC12-37 cells. In contrast, caffeine-induced Ca2+ influx in PC12-37 cells is similar to that observed in PC12 cells, indicating that caffeine-induced CA2+ influx is neither mediated by caffeine-induced Ca2+ release nor contributes to the caffeine-induced secretion. These results show (a) a tight coupling between caffeine activation of a ryanodine-sensitive Ca2+ store and transmitter release, (b) no significant involvement of the ryanodine-sensitive Ca2+ channel in depolarization- and agonist-mediated transmitter release, and (c) exclude a major role for caffeine-mediated Ca2+ entry in the caffeine-activated secretion.

Effects of bradykinin on [3H]-norepinephrine release in rat hypothalamus

1. We examined the regulatory actions of bradykinin on norepinephrine release in the hypothalamus of rats. 2. Bradykinin increased the stimulation-evoked [3H]-norepinephrine release from hypothalamic slices of Sprague-Dawley rats in a dose-dependent manner (1 Hz: S2/S1 ratio, mean +/- s.e.m., control 0.868 +/- 0.016, n = 6; bradykinin 1 x 10(-6) mol/L 1.039 +/- 0.018, n = 6, P < 0.05; bradykinin 3.3 x 10(-6) mol/L 1.130 +/- 0.064, n = 6, P < 0.05). The basal release of [3H]-norepinephrine was not affected by the peptide. 3. Bay K 8644, a dihydropyridine-sensitive calcium channel agonist, significantly potentiated the facilitatory effect of bradykinin on norepinephrine release, although Bay K 8644 by itself had no significant effect. By contrast, nicardipine, a dihydropyridine-sensitive calcium channel blocker, reversed the increase in norepinephrine release induced by bradykinin and Bay K 8644. 4. These results indicate that bradykinin may increase norepinephrine release in rat hypothalamus, partially mediated by interactions with dihydropyridine-sensitive calcium channels.

Cobalt uptake enables identification of capsaicin- and bradykinin-sensitive subpopulations of rat dorsal root ganglion cells in vitro

A novel modification of the stimulated cobalt uptake technique has been used to identify rat dorsal root ganglion cells expressing capsaicin and bradykinin receptors. The technique involves incubating intact dorsal root ganglia in vitro in a modified Krebs solution in which cobalt chloride has been substituted for calcium. Activation of dorsal root ganglion cells by capsaicin or bradykinin in the presence of the cobalt ions results in cobalt influx into the excited cells. Histochemical methods were then used to visualize the intracellular accumulation of cobalt, and labelled cells were counted and characterized. Capsaicin (2 microM) or bradykinin (500 nM) applied for 20 min induced cobalt uptake in 13.8 +/- 0.6 and 9.6 +/- 0.5% of neuronal profiles in dorsal root ganglia (L4), respectively, a significantly larger number than stained in control ganglia (in the absence of agonists: 1.8 +/- 0.7%). The longest diameter of the soma of stained dorsal root ganglion cells following capsaicin and bradykinin perfusion were significantly different from each other and from the non-labelled population (17.5 +/- 0.7 and 24.5 +/- 0.2 microns for capsaicin; 23.2 +/- 0.9 and 25.5 +/- 0.4 microns for bradykinin; labelled and non-labelled cells, respectively). The distribution of cell diameters revealed that while capsaicin-sensitive cells were exclusively small-sized, bradykinin-sensitive cells were predominantly small and medium sized. The selective bradykinin-2 receptor antagonist HOE-140 (5.0 microM) blocked the bradykinin-induced staining (2.16 +/- 0.02%) but not that of capsaicin. The bradykinin-1 agonist [des-Arg9]-bradykinin did not induce any significant increase in stained cells over the control number (2.2 +/- 0.7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Further substantiation of a significant role for the sympathetic nervous system in inflammation

This study provides significant new evidence substantiating a role of the postganglionic sympathetic neuron in plasma extravasation in the knee-joint of the rat. Increased plasma extravasation produced by the potent inflammatory mediator bradykinin was mimicked by 6-hydroxydopamine, a selective stimulator of sympathetic fibers. Various treatments (chemical sympathectomy, co-perfusion with the local anesthetic lidocaine, or co-perfusion with depolarizing concentrations of potassium) similarly modulated plasma extravasation induced by both bradykinin and 6-hydroxydopamine, but not that produced by platelet activating factor. We also showed that bradykinin is able to release norepinephrine in the knee-joint, indicating action on the sympathetic postganglionic neuron. In summary, these experiments provide substantial additional evidence supporting a significant contribution of the sympathetic post-ganglionic neuron terminal to inflammatory plasma extravasation.

Bradykinin-induced ion currents in cultured rat trigeminal ganglion cells

Effects of bradykinin (BK) on membrane currents of cultured rat trigeminal ganglion cells were studied with a G omega-sealed discontinuous voltage clamp technique. Bradykinin (0.05 nM-1 microM) produced membrane depolarization in most cells and hyperpolarization in some cells via a variety of ionic mechanisms: (1) activation of a cation current, (2) enhancement or (3) inhibition of a hyperpolarization-activated inwardly rectifying cation current known as IH, (4) reduction or (5) enhancement of an outwardly rectifying outward current (presumably a delayed K+ current), (6) inhibition of a slow-gating voltage-dependent steady-state outward current (at > -55 mV) and/or (7) increase in another slow-gating voltage-dependent outward current (at > or = -70 mV). These components of BK-induced currents appeared in different combinations and extents among cells, explaining complex excitatory and modulatory actions of BK in different regions and types of sensory neurons.

Intracellular calcium, currents, and stimulus-response coupling in endothelial cells

Vascular endothelium appears to be a unique organ. It not only responds to numerous hormonal and chemical signals but also senses changes in physical parameters such as shear stress, producing mediators that modulate the responses of numerous cells, including vascular smooth muscle, platelets, and leukocytes. In many cases, the initial response of endothelial cells to these diverse signals involves elevation of cytosolic Ca2+ and activation of Ca(2+)-dependent enzymes, including nitric oxide synthase and phospholipase A2. Both the release of Ca2+ from intracellular stores, most likely the endoplasmic reticulum, and the influx of Ca2+ from the extracellular space contribute to the [Ca2+]i increase. The most important trigger for Ca2+ release is inositol 1,4,5-trisphosphate, which is generated by the action of phospholipase C, a plasmalemmal enzyme activated in many cases by the receptor-G protein cascade. Ca2+ influx appears to be related to the activity of receptor-G protein-enzyme complex and to the degree of fullness of the endoplasmic reticulum but does not involve voltage-gated Ca2+ channels. The magnitude of the Ca2+ influx depends on the electrochemical gradient, which is modulated by the membrane potential, Vm. Under basal conditions, Vm is dominated by a large inward rectifier K+ current. Some stimuli, e.g., acetylcholine, have been shown to hyperpolarize Vm, thus increasing the electrochemical gradient for Ca2+, which appears to be modulated by activation of Ca(2+)-dependent K+ and Cl- currents. However, the lack of potent and specific blockers for many of the described or postulated channels (e.g., nonselective cation channel, Ca(2+)-activated Cl- channel) makes an estimation of their effect on endothelial cell function rather difficult. Possible future directions of research and clinical implications are discussed.

Potency of depolarization-induced transmitter release is determined by divalent cation influx in PC 12 cells

Evoked release of [3H]dopamine ([3H]DA) from pheochromocytoma cells (PC 12) is dependent on extracellular calcium ([Ca2+]ex), but it can take place if calcium ions (Ca2+) are substituted by other divalent ions such as strontium (Sr2+) and barium (Ba2+). The potency of the divalent cations at supporting release varies with the cell type; in PC 12 cells the order of potency is Ba2+ > Sr2+ > Ca2+. The close correlation between depolarization-evoked Ca2+ entry and depolarization-evoked transmitter release prompted us to examine whether the higher evoked transmitter release in the presence of Sr2+ correlates with an increased evoked Sr2+ influx. Influx studies were conducted on PC12 cells using a radioactive tracer (45Ca2+ or 85Sr2+, < 1 microM) in the presence of either Sr2+ (0.5 mM) or Ca2+ (0.5 mM). Depolarization with K Cl (60 mM) increased evoked 45Ca2+ influx 2-fold when Ca2+ was substituted with Sr2+. Similarly, evoked 85Sr2+ influx increased 1.87-fold by substituting Ca2+ for Sr2+. Thus the amount of evoked cation influx is determined by the type of divalent ion which is accessible in the extracellular medium, independently of the radioactive tracer used. Increased evoked transmitter release in the presence of Sr2+ was associated with increased evoked Sr2+ influx. This suggests that the potency of evoked transmitter release is determined predominantly by the influx of divalent cations. Furthermore, the steps subsequent to cation influx in the release process are equally efficient for both cations.