Interleukin-1 inhibits voltage-dependent P/Q-type Ca2+ channel associated with the inhibition of the rise of intracellular free Ca2+ concentration and catecholamine release in adrenal chromaffin cells

Effects of interleukin (IL) on intracellular free Ca2+ concentration ([Ca2+]i) rise and catecholamine (CA) release were examined in isolated, cultured bovine adrenal chromaffin cells. IL-1α and IL-1β inhibited the rise of [Ca2+]i and CA release induced by acetylcholine (ACh) and excess KCl both in normal and in Ca2+-sucrose medium. IL-1 receptor antagonist, IL-1RA by pretreatment blocked the inhibitory actions of IL-1. IL-1α reduced CA release induced by veratridine in normal medium but not in the presence of diltiazem. Analysis using specific blockers for voltage-operated Ca2+ channels revealed that IL-1α specifically inhibited the P/Q-type Ca2+ channel to reduce [Ca2+]i rise induced by excess KCl. IL-1 did not affect [Ca2+]i rise induced either by bradykinin or caffeine in Ca2+- deprivated medium or via activation of store-operated Ca2+ channel. The inhibitory effects of IL-1 were blocked by pretreatments of cells with herbimycin A, U0126 and PD 98054, but not with SB202190, SP 600125 or pertussis toxin (PTX), inhibited the induction of the inhibitory action of IL-1.These results demonstrated that IL-1 inhibits stimulation-evoked [Ca2+]i rise and CA release in chromaffin cells by blocking voltage-operated P/O-type Ca2+ channels. The inhibitory action of IL-1 may be mediated through tyrosine kinase and MEK/ERK pathways

MPP+ toxicity and plasma membrane dopamine transporter: study using cell lines expressing the wild-type and mutant rat dopamine transporters

AbstractThe Parkinsonism-inducing neurotoxin 1-methyl-4-phenylpyridinium (MPP+) causes specific cell death in dopaminergic neurons after accumulation by the dopamine transporter (DAT). COS cells, a non-neuronal cell line insensitive to high doses of MPP+, becomes sensitive to MPP+ when transfected with the rat DAT cDNA. We analyzed the bi-directional transport of MPP+ and its toxicity in several cell lines expressing wild or mutant DATs. Cell death in COS cells expressing wild DAT by exposure to MPP+ was concentration-dependent and cocaine-reversible. Increased wild DAT expression caused higher sensitivities to the toxin in HeLa cells. Although several mutant DATs demonstrated greater transport activity than the wild-type, they displayed similar or lower sensitivity to MPP+ toxicity. Reverse transport of preloaded [3H]MPP+ through DAT was facilitated in COS cells expressing certain mutant DATs, which consistently displayed less sensitivity to MPP+ toxicity. These results suggest that re-distribution of MPP+ due to influx/efflux turnover through the transporter is a key factor in MPP+ toxicity

MPP+ toxicity and plasma membrane dopamine transporter: study using cell lines expressing the wild-type and mutant rat dopamine transporters

AbstractThe Parkinsonism-inducing neurotoxin 1-methyl-4-phenylpyridinium (MPP+) causes specific cell death in dopaminergic neurons after accumulation by the dopamine transporter (DAT). COS cells, a non-neuronal cell line insensitive to high doses of MPP+, becomes sensitive to MPP+ when transfected with the rat DAT cDNA. We analyzed the bi-directional transport of MPP+ and its toxicity in several cell lines expressing wild or mutant DATs. Cell death in COS cells expressing wild DAT by exposure to MPP+ was concentration-dependent and cocaine-reversible. Increased wild DAT expression caused higher sensitivities to the toxin in HeLa cells. Although several mutant DATs demonstrated greater transport activity than the wild-type, they displayed similar or lower sensitivity to MPP+ toxicity. Reverse transport of preloaded [3H]MPP+ through DAT was facilitated in COS cells expressing certain mutant DATs, which consistently displayed less sensitivity to MPP+ toxicity. These results suggest that re-distribution of MPP+ due to influx/efflux turnover through the transporter is a key factor in MPP+ toxicity

Transport of dopamine and levodopa and their interaction in COS-7 cells heterologously expressing monoamine neurotransmitter transporters and in monoaminergic cell lines PC12 and SK-N-SH

The present study investigated the effects of levodopa, a precursor of dopamine (DA) therapeutically used for the treatment of Parkinson's disease, on DA transport in the two different systems, COS-7 cells heterologously expressing rat monoamine transporter cDNA and in monoaminergic cell lines PC12 and SK-N-SH. Levodopa enhanced uptake of [3H]DA and [3H]norepinephrine (NE) but not [3H]serotonin in the transfected COS-7 cells in a concentration-dependent manner. On the other hand, in PC12 and SK-N-SH cells where NET is functionally expressed, levodopa enhanced [3H]DA and [3H]NE uptake at low concentrations and inhibited the uptake at higher concentrations. The effects of levodopa on catecholamine transporters in the opposite direction suggest a different mechanism at the intra- and extracellular sites in a levodopa transport-dependent and independent manner

Development of tactile allodynia and thermal hyperalgesia by intrathecally administered platelet-activating factor in mice

Platelet-activating factor (PAF) is a potent inflammatory lipid mediator in peripheral tissues. However, its role in mediation of nociception in central nervous system is unknown. In the present study, whether PAF plays some role in pain transduction in the spinal cord was studied in mice. Intrathecal injection of PAF induced tactile pain, tactile allodynia at as low as 10 fg ~ 1 pg with a peak response at 100 fg, while lyso-PAF was without effect in the range of doses. Tactile allodynia induced by PAF was blocked by a PAF receptor antagonists, TCV-309, WEB 2086 and BN 50739. The expression of PAF receptor mRNA by RT-PCR was observed in DRG and spinal cord in mice. ATP P2X receptor antagonists, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) and 2',3'-O-(2,4,6-trinitrophenyl) adenosine 5-triphosphate (TNP-ATP), NMDA receptor antagonist, MK 801 and nitric oxide synthetase inhibitor, 7-nitroindazole blocked the PAF-induced tactile allodynia. PAF-induced tactile allodynia and thermal hyperalgesia disappeared in neonatally capsaicin-treated adult mice, while tactile allodynia but not thermal hyperalgesia induced by intrathecally injected α,β-methylene ATP, a P2X receptor agonist, was capsaicin-insensitive. The present study demonstrated that PAF is a potent inducer of tactile allodynia and thermal hyperalgesia at the level of the spinal cord. PAF-evoked tactile allodynia is suggested to be mediated by ATP and the following NMDA and NO cascade through capsaicin-sensitive fiber, different from exogenously injected α,β-methylene ATP which is insensitive to capsaicin treatment

Mechanisms of pain sensitization and the treatments

Hyperalgesia and allodynia, major symptoms of neuropathic pain can results after nerve injury or chronic inflammation. Trigeminal neuropathic pain resulting from alterations in peripheral and central noxious transmission systems often produced after nerve injury by pulpectomy or tooth-extraction or from temporomandibular joint inflammation. Neuropathic also occurs in some disease state, diabetic peripheral neuropathy, post-herpetic neuropathy and trigeminal neuralgia. Allodynia is characterized by long lasting pain evoked by essentially non-painful stimuli such as just light touch and tolerance to medication with conventional analgesics.Neuropathic pain is probably not a result of a single pathological mechanism, but the final product of an altered peripheral and central processing. Recent advances in pain research revealed that many factors derived from neurons and also non-neuronal neighboring residents participate in the initiation, development and maintenance. Among them, lipid mediators such as prostaglandins, lysophosphatidic acid and platelet-activating factor are recently found to play conspicuous roles for development of allodynia and hyperalgesia in spinal cord. Further advance by using cellular biological and molecular techniques would dig into the mechanisms underlying neuropathic pain and illustrate the new strategy and target candidate for drug development.There are also needs for tools and methods to assess neuropathic pain, common guidelines on classification, diagnosis and management, and evidence-based approach to the treatment of neuropathic pain

Chronic inhibition of the norepinephrine transporter in the brain participates in the seizure sensitization to cocaine and local anesthetics

Involvement of chronic inhibition of monoamine transporters (MAT) in the brain concerning the sensitization of cocaine- and local anesthetic-induced seizures was studied in mice. Repeated administration of subconvulsive doses of meprylcaine as well as cocaine, both of which inhibit MAT, but not lidocaine, which does not inhibit MAT, increased seizure activity and produced sensitization to other local anesthetics. Effects of 5 daily treatments of monoamine transporter inhibitors on lidocaine-induced convulsions were examined 2 or 3 days after the last dose of the inhibitors. The daily treatments of GBR 12935, a specific inhibitor of dopamine uptake, significantly increased the incidence and the intensity of lidocaine-induced convulsions at 20 mg/kg and decreased the threshold of the convulsions. The daily treatments of desipramine and maprotiline, selective norepinephrine uptake inhibitors, markedly increased the incidence and intensity of lidocaine-induced convulsions, and decreased the threshold with dose-dependent manner between 5 and 20 mg/kg. The daily treatments of citaloplam, a selective serotonin uptake inhibitor, 10 and 20 mg/kg, produced no significant increase in the incidence or intensity of lidocaine-induced convulsions but decreased the threshold of the convulsions. These results suggest that the chronic intermittent inhibition of monoamine uptake increases susceptibility to cocaine- and local anesthetic-induced seizures, and a norepinephrine transporter is an integral component of this sensitization

Inhibition of serotonin transporters by cocaine and meprylcaine

The present study examined whether the inhibition of serotonin transporters (SERT) contributes to cocaine- and other local anesthetics-induced convulsions, and which subtypes of 5-HT receptor are involved in the convulsions. For this purpose, cocaine, meprylcaine and lidocaine, all of which have different effects on SERT, were used as convulsants and the effects of serotonin reuptake inhibitors (SSRIs), specific agonists and antagonists for 5-HT receptor subtypes were evaluated in mice.Administration of SSRI, zimelidine, citalopram and fluoxetine, 5-HT2A,2C receptor agonist, R(-)-DOI and the 5-HT2C receptor agonists, mCPP and MK212 resulted in a marked increase in incidence of convulsions and a reduction in the threshold of lidocaine-induced convulsions, while the 5-HT2B receptor agonist, BW723C86, had little influence. On the other hand, SSRI did not affect the measured parameters in meprylcaine- and cocaine-induced convulsions. R(-)-DOI, mCPP and MK212 reduced the threshold of meprylcaine or cocaine with less extent than the reduction of lidocaine threshold. Incidence of cocaine- and meprylcaine-induced convulsions were significantly reduced by 5-HT2A,2B,2C antagonist, LY-53857 and 5-HT2C antagonist, RS 102221. The threshold of cocaine and meprylcaine was significantly increased by both antagonists. 5-HT2A antagonists MDL-11,939 and ketanserin, and 5-HT2B antagonist SB-204741 except at high doses had little effect on cocaine- and meprylcaine-induced convulsions. None of these antagonists altered the parameters of lidocaine-induced convulsions. Pretreatment with fluoxetine but not citalopram increased the plasma concentration of lidocaine. These results suggest that the increase of serotonergic neuronal activity through 5-HT2C receptor stimulation was responsible for increased activity of local anesthetics-induced convulsions and support the involvement of this mechanism in cocaine- and meprylcaine- but not in lidocaine- induced convulsions through their direct inhibitory action on central SERT