U-92032, a T-type Ca2+ channel blocker and antioxidant, reduces neuronal ischemic injuries

The T-type calcium channel enhancer SAK3 inhibits neuronal death following transient brain ischemia via nicotinic acetylcholine receptor stimulation

The T-type calcium channel enhancer SAK3 (ethyl 8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo[1,2-a]pyridin]-2-ene-3-carboxylate) promotes acetylcholine (ACh) release in mouse hippocampus, enhancing cognitive function. Here, we tested SAK3 neuroprotective activity in the context of transient brain ischemia using a 20-min bilateral common carotid arteries occlusion (BCCAO) mouse model. Mice were administered with SAK3 (0.1, 0.5 or 1.0 mg/kg, p.o.) 24 h after BCCAO ischemia. Oral SAK3 (0.5 or 1.0 mg/kg/day, p.o.) administration significantly blocked loss of hippocampal CA1 neurons and memory deficits seen in BCCAO mice. Treatment with α7 nicotinic ACh receptor (nAChR)-selective inhibitor methyllycaconitine (MLA: 6.0 mg/kg/day, i.p.) significantly antagonized both neuroprotection and improvement in memory promoted by SAK3 (0.5 mg/kg/day, p.o.). Acute SAK3 (0.5 mg/kg, p.o.) administration significantly enhanced protein kinase B (Akt) phosphorylation levels in CA1 of control and BCCAO mice. Importantly, treatment of control and BCCAO mice with the non-selective nAChR antagonist mecamylamine (MEC: 1.0 mg/kg, i.p.) or the α7-selective nAChR antagonist MLA (6.0 mg/kg, i.p.), but not the M1 muscarinic ACh receptor (mAChR) antagonist pirenzepine (PZ: 10 mg/kg, i.p.), blocked enhanced Akt activity elicited by SAK3 (0.5 mg/kg, p.o.). We also confirmed that decreased phosphorylated Akt immunoreactivities were rescued by SAK3 (0.5 mg/kg, p.o.) administration in NeuN-positive CA1 neurons of BCCAO mice, an effect blocked by MLA (6.0 mg/kg, i.p.). Finally, we observed α7 nAChR and phosphorylated Akt expression in CA1 pyramidal neurons. We conclude that the T-type calcium channel enhancer SAK3 is neuroprotective in the context of brain ischemia by stimulating nicotinic cholinergic neurotransmission.

The new pyridoindole antioxidant SMe1EC2 and its intervention in hypoxia/hypoglycemia-induced impairment of longterm potentiation in rat hippocampus

Previously, the pyridoindole SMe1EC2 was proved to inhibit lipoperoxidation and carbonylation of proteins in rat brain cortex in the system Fe²⁺/ascorbate and improvement of resistance of the rat hippocampus was reported against ischemic conditions in vitro (hypoxia/hypoglycemia) expressed by the enhanced neuronal response recovery in reoxygenation. The hippocampus fulfils many of the criteria for a neuronal correlate of learning and memory. Recently, an impairment of hippocampal long-term potentiation (LTP) was reported under oxidative stress. Different therapies, including antioxidants, have been studied intensively concerning the impairment of neuronal plasticity. In this study marked reduction of LTP, elicited by a single burst (100 Hz, 1s) in the CA3-CA1 area of rat hippocampal slices, was shown due to transient hypoxia/hypoglycemia compared to control slices. On the basis of previously reported antioxidant and neuroprotective effects of SMe1EC2, its effect on loss of LTP in the hippocampus due to ischemic conditions was studied in vitro. The pyridoindole tested improved hypoxia/hypoglycemia-induced reduction of LTP compared to untreated hypoxic slices. An opposite effect of SMe1EC2 on LTP induction was found in control slices. The mechanism of SMe1EC2 action on LTP in ischemic conditions has been suggested to differ from the mechanism of its effect in “normoxia” and may be due to different redox status in control and ischemic brain tissue. The manifested LTP-protective effect of SMe1EC2 observed in the rat hippocampus exposed to ischemia in vitro may find exploitation in therapy associated with injured neuronal plasticity in some conditions, including ischemia, trauma and aging in man.

Effect of Saffron (Crocus sativus) on Neurobehavioral and Neurochemical Changes in Cerebral Ischemia in Rats

The modifying effects of Crocus sativus (CS) stigma extract on neurobehavioral activities, malondialdehyde (MDA), reduced glutathione (GSH), glutathione peroxidase, glutathione reductase, glutathione S-transferase, superoxide dismutase (SOD), catalase (CAT), and Na(+),K(+)-ATPase activities, and glutamate (Glu) and aspartate (Asp) content were examined in the middle cerebral artery (MCA) occlusion (MCAO) model of acute cerebral ischemia in rats. The right MCA of male Wistar rats was occluded for 2 hours using intraluminal 4-0 monofilament, and reperfusion was allowed for 22 hours. MCAO caused significant depletion in the contents of GSH and its dependent enzymes while significant elevation of MDA, Glu, and Asp. The activities of Na(+),K(+)-ATPase, SOD, and CAT were decreased significantly by MCAO. The neurobehavioral activities (grip strength, spontaneous motor activity, and motor coordination) were also decreased significantly in the MCAO group. All the alterations induced by ischemia were significantly attenuated by pretreatment of CS (100 mg/kg of body weight, p.o.) 7 days before the induction of MCAO and correlated well with histopathology by decreasing the neuronal cell death following MCAO and reperfusion. The present results may suggest the effectiveness of CS in focal ischemia most probably by virtue of its antioxidant property.

Actions of U-92032, a T-type Ca2+ channel antagonist, support a functional linkage between I(T) and slow intrathalamic rhythms

Thalamic relay neurons express high levels of T-type Ca(2+) channels, which support the generation of robust burst discharges. This intrinsically mediated form of phasic spike firing is thought to be critical in the generation of slow (3-4 Hz) synchronous oscillatory activity of absence epilepsy. Recordings made from brain slices or whole animals have shown that slow synchronous absence-like activity can be abolished when Ca(2+)-dependent burst firing in relay neurons is interrupted by the pharmacological or genetic inactivation of T-channels. Because succinimide drugs act as incomplete and nonspecific antagonists, we tested whether the novel T-channel antagonist U-92032 could provide stronger support for a role of T-channels in slow oscillatory activity. Ca(2+)-dependent rebound (LTS) bursts were recorded using whole cell current clamp in relay cells of the ventral basal complex (VB) from thalamic slices of adult rats. We used LTS kinetics to measure the availability of T-channels in VB cells after TTX. U-92032 (1 and 10 microM) reduced the maximum rate of depolarization of the isolated LTS by 51% and 90%, respectively, compared with the 35% reduction due to 2 mM methylphenylsuccinimide (MPS), the active metabolite of the antiabsence drug methsuximide. U-92032 (1 and 10 microM) also suppressed evoked, slow oscillations in thalamic slices with a time course similar for observed intracellular effects. Unlike MPS, we observed no substantial effects of short-term U-92032 applications (< or =2 h) on the generation of action potentials in VB cells. Our findings show U-92032 is a more potent, effective, and specific T-channel antagonist than previously studied succinimide antiabsence drugs and that it dramatically reduces epileptiform synchronous activity. This suggests that U-92032 or other specific T-channel antagonists may provide effective drug treatments for absence epilepsy.

Novel diphenylalkyl piperazine derivatives with dual calcium antagonistic and antioxidative activities

Two types of novel diphenylalkyl piperazine derivatives containing the thio or aminopropanol moiety substituted by phenyl or benzyl group were synthesized, and evaluated for their calcium antagonistic and antioxidative activities. These compounds showed apparent inhibitions against KCl-induced contractions in isolated rat aorta. Among them, phenylamino compound 9 and benzylamino compound 13 also possessed potent inhibitory activities against auto-oxidative lipid peroxidations in canine brain homogenates. Two representative compounds 3a and 9 were evaluated for their inhibitory activities against KCl-induced contractions in isolated canine arteries (basilar, coronary, mesenteric, and renal). Both compounds showed the most potent inhibitions to basilar artery.

Effects of ibudilast on hippocampal long-term potentiation and passive avoidance responses in rats with transient cerebral ischemia

The present study evaluated the effects of ibudilast on impaired passive avoidance responses and hippocampal long-term potentiation (LTP) caused by transient cerebral ischemia in rats. The hippocampal nerve cell density was also measured. The latency determined in retention trials of passive avoidance shortened significantly in the 4-vessel occlusion (4VO) group (in which four blood vessels were occluded for 20 min to cause cerebral ischemia). A significant recovery in the latency was observed by administration of ibudilast (10 mg kg (-1)). The population spike amplitude in both the hippocampal CA1 region and perforant path-dentate gyrus synapses was potentiated by tetanus stimulation in the sham-operated group, while in the 4VO group, LTP was significantly inhibited. This inhibition was reversed by administration of ibudilast (10 mg kg (-1)). A marked reduction of cell densities in the CA1 region was observed in the 4VO group compared with the normal group. The nerve cell density in the hippocampal CA1 region was decreased by 20 min of cerebral ischemia. Ibudilast significantly inhibited the reduction of cell densities in a dose-dependent manner. In contrast, the cell density in the dentate gyrus was comparable in the 4VO and normal groups, and no significant changes were observed in the ibudilast groups. These findings suggest that ibudilast might possess neuronally protective properties, i.e. protecting neurons not only from deaths but also from functional damage due to certain cerebral ischemia.

Synthesis and biological evaluation of new 4-arylpiperidines and 4-aryl-4-piperidinols: dual Na(+) and Ca(2+) channel blockers with reduced affinity for dopamine D(2) receptors

A series of novel 4-arylpiperidines and 4-aryl-4-piperidinols (2a-f, 3a-f and 4a-f) was synthesized and evaluated for blocking effects on both neuronal Na(+) and T-type Ca(2+) channels and binding affinity for dopamine D(2) receptors. Most of the compounds blockaded both ion channels with potency greater than or equal to flunarizine 1a which was adopted as a reference standard. In addition, these compounds had significantly reduced affinity for dopamine D(2) receptors which is common in this class of structure. Compounds 2a-f, 3a-f and 4a-f exhibited potent anticonvulsant effects following systemic (ip) administration on audiogenic seizures in DBA/2 mice, indicating their excellent brain permeability. The neuroprotective activity of 2a, 3a and 4a was also assessed in a transient middle cerebral artery occlusion (MCAO) model. These compounds significantly reduced neuronal damage without affecting ischemic hyperthemia, while flunarizine 1a produced only minor reductions. In particular, 4a had 1.7-fold the potency in this MCAO model but only 1/20 the affinity for dopamine D(2) receptors of 1a. The superposition of 2a, 3a and 4a on the basis of analyses of systematic conformation and similar structure has revealed that the cinnamyl, phenacyl and phenoxypropanol groups are likely to be structurally and biologically equivalent. Moreover, the superposition of 2a and 2f shows that diphenyl ether and biphenyl groups occupy a similar space, suggesting that both groups act as a bioisostere for the blockade of ion channels; however, this is not the case for dopamine D(2) receptors since only biphenyl compounds such as 2f had high affinity similar to flunarizine 1a. Compound 4a (SUN N5030) has a good pharmacological profile and may be useful in the alleviation and treatment of ischemic diseases.

Differential inhibition of T-type calcium channels by neuroleptics

T-type calcium channels play critical roles in cellular excitability and have been implicated in the pathogenesis of a variety of neurological disorders including epilepsy. Although there have been reports that certain neuroleptics that primarily target D2 dopamine receptors and are used to treat psychoses may also interact with T-type Ca channels, there has been no systematic examination of this phenomenon. In the present paper we provide a detailed analysis of the effects of several widely used neuroleptic agents on a family of exogenously expressed neuronal T-type Ca channels (alpha1G, alpha1H, and alpha1I subtypes). Among the neuroleptics tested, the diphenylbutylpiperidines pimozide and penfluridol were the most potent T-type channel blockers with Kd values (approximately 30-50 nm and approximately 70-100 nm, respectively), in the range of their antagonism of the D2 dopamine receptor. In contrast, the butyrophenone haloperidol was approximately 12- to 20-fold less potent at blocking the various T-type Ca channels. The diphenyldiperazine flunarizine was also less potent compared with the diphenylbutylpiperadines and preferentially blocked alpha1G and alpha1I T-type channels compared with alpha1H. The various neuroleptics did not significantly affect T-type channel activation or kinetic properties, although they shifted steady-state inactivation profiles to more negative values, indicating that these agents preferentially bind to channel inactivated states. Overall, our findings indicate that T-type Ca channels are potently blocked by a subset of neuroleptic agents and suggest that the action of these drugs on T-type Ca channels may significantly contribute to their therapeutic efficacy.

Effect of nordihydroguaiaretic acid on behavioral impairment and neuronal cell death after forebrain ischemia

The purpose of this study was to evaluate the neuroprotective effect of nordihydroguaiaretic acid (NDGA), an antioxidant and/or 5-lipoxygenase inhibitor, on ischemia-reperfusion injury behavioral pharmacologically and histologically in vivo. First, the antioxidant activity of NDGA was evaluated in vitro by measuring the production of thiobarbituric acid reactive substances (TBARS) in rat brain homogenate. Second, the effect of NDGA on learning and memory impairment induced by rat four-vessel occlusion transient ischemia was investigated with the Morris water-maze task. Third, the effect of NDGA on pyramidal cell loss in the hippocampus after transient ischemia was examined. NDGA inhibited the production of TBARS with an IC(50) of 0.1 microM, and significantly attenuated postischemic learning and memory impairment at 10 mg/kg. Furthermore, consecutive 4-day administration of NDGA at 10 mg/kg significantly reduced the postischemic neuronal death. NDGA was found to be potent and effective as an anti-ischemia-reperfusion injury agent in terms of behavioral pharmacology and histology. The present results suggest that NDGA has beneficial effects on behavioral deficits and histological injury caused by ischemia-reperfusion.

Molecular pharmacology of T-type Ca2+ channels

Over the past few years increasing attention has been focused on T-type calcium channels and their possible physiological and pathophysiological roles. Efforts toward elucidating the exact role(s) of these calcium channels have been hampered by the lack of T-type specific antagonists, resulting in the subsequent use of less selective calcium channel antagonists. In addition, the activity of these blockers often varies with cell or tissue type, as well as recording conditions. This review summarizes a variety of compounds that exhibit varying degrees of blocking activity towards T-type Ca2+ channels. It is designed as an aid for researchers in need of antagonists to study the biophysical and pathological nature of T-type channels, as well as a starting point for those attempting to develop potent and selective antagonists of the channel.

Flunarizine improves the survival of grafted dopaminergic neurons

Embryonic nigral grafts can survive, reinnervate the striatum and reverse functional deficits in both experimental and clinical Parkinsonism. A major drawback is that only around 10% of the implanted dopaminergic neurons survive. The underlying mechanisms leading to this 90% cell death are not fully understood, but oxidative stress and a substantial loss of neurotrophic support are likely to be involved. Hypoxia and mechanical trauma, which are unavoidable during tissue preparation, may be a trigger for cell death. Recent studies have provided evidence that the type of cell death occurring is, to a large extent, apoptotic. Flunarizine is an antagonist of L-, T- and N-type calcium channels, which permits calcium entry into cells via a voltage-dependent mechanism. Flunarizine has been shown to protect neurons against death induced by serum deprivation, nerve growth factor deprivation, oxidative stress, axotomy and ischemia. This study was designed to investigate whether flunarizine can protect grafted embryonic dopaminergic neurons from death when implanted in a rat model of Parkinson's disease. Addition of 1 microM flunarizine inhibited cell death in a suspension of cells derived from the rat's ventral mesencephalon and when such a treated suspension was injected into the neostriatum there was a 2.6-fold greater number of surviving dopaminergic neurons, a doubling of the graft volume and a doubling of the volume of the host neostriatum innervated by dopaminergic fibers from the graft, compared with suspensions not exposed to flunarizine. Furthermore, rats injected with cells that had been exposed to flunarizine displayed a greater recovery of function in the amphetamine-induced rotation test.

Efficient functional coupling of the human D3 dopamine receptor to G(o) subtype of G proteins in SH-SY5Y cells

1 The D3 dopamine receptor presumably activates Gi/Go subtypes of G-proteins, like the structurally analogous D2 receptor, but its signalling targets have not been clearly established due to weak functional signals from cloned receptors as heterologously expressed in mostly non-neuronal cell lines. 2 In this study, recombinant human D3 receptors expressed in a human neuroblastoma cell line, SH-SY5Y, produced much greater signals than those expressed in a human embryonic kidney cell line, HEK293. Quinpirole, a prototypic agonist, markedly inhibited forskolin-stimulated cyclic AMP production and Ca2+-channel (N-type) currents in SH-SY5Y cells, and enhanced GTPgamma35S binding in isolated membranes, nearly ten times greater than that observed in HEK293 cell membranes. 3 GTPgamma35S-bound Galpha subunits from quinpirole-activated and solubilized membranes were monitored upon immobilization with various Galpha-specific antibodies. Galphao subunits (not Galphai) were highly labelled with GTPgamma35S in SH-SY5Y, but not in HEK293 cell membranes, despite their abundance in the both cell types, as shown with reverse transcription-polymerase chain reaction and Western blots. N-type Ca2+ channels and adenylyl cyclase V (D3-specific effector), on the other hand, exist only in SH-SY5Y cells. 4 More efficient coupling of the D3 receptor to Go subtypes in SH-SY5Y than HEK293 cells may be attributed, at least in part, to the two D3 neuronal effectors only present in SH-SY5Y cells (N-type Ca2+-channels and adenylyl cyclase V). The abundance of Go subtypes in the both cell lines seems to indicate their availability not a limiting factor.

A novel class of Na+ and Ca2+ channel dual blockers with highly potent anti-ischemic effects

A series of novel arylpiperidines (4a-d) which have highly potent blocking effects for both neuronal Na+ and T-type Ca2+ channels with extremely low affinity for dopamine D2 receptors were synthesized. Among these compounds, 1-(2-hydroxy-3-phenoxy)propyl-4-(4-phenoxyphenyl)-piperidine hydrochloride (4c; SUN N5030) exhibited remarkable neuroprotective activity in a transient middle cerebral artery occlusion (MCAO) model.

Neuroprotective effects of a novel broad-spectrum cation channel blocker, LOE 908 MS, on experimental focal ischemia: a multispectral study

Thirty-four rats undergoing 90 minutes of temporary middle cerebral artery occlusion were randomly and blindly assigned to vehicle or (RS)-(3,4-dihydro-6, 7-dimethoxyisoquinoline-1-gamma1)-2-phenyl-N,N-di-2-(2, 3, 4-trimethoxyphenyl)ethyl acetamide (LOE 908 MS; 0.5 mg/kg) i.v. bolus at 30 minutes after arterial occlusion followed by a 5 mg/kg/hr i.v. infusion for 3.8 hours (n =17/group). Perfusion-, diffusion- and T(2)-weighted magnetic resonance imaging was performed before treatment and repeatedly after treatment. Multispectral analysis was used to define ischemic abnormalities. The size of the ischemic abnormalities, including the ischemic core and penumbra, was not different between the two groups before treatment. However, a significant difference in ischemic lesion size was detected beginning 1.5 hours after treatment. The size of the ischemic core was significantly smaller in the treatment group, while the size of the ischemic penumbra was similar in the two groups at 85 minutes after arterial occlusion. Postmortem infarct size at 24 hours was significantly smaller in the drug-treated group than in the placebo group. These results demonstrate that LOE 908 MS can reduce ischemic lesion size, which is probably attributable to inhibition of expansion of the ischemic core. J. Magn. Reson. Imaging 1999;10:138-145.

A calcium antagonist protects against doxorubicin-induced impairment of calcium handling in neonatal rat cardiac myocytes

The effects of doxorubicin (DOX) on intracellular calcium transients and the cardioprotective effects of a calcium antagonist on DOX-induced impairment of calcium handling were examined in neonatal rat cultured cardiac myocytes. Cultured cardiac myocytes isolated from neonatal Wistar-Kyoto rats were treated with DOX for 24 h. Field-stimulated calcium transients in single myocytes were measured in the presence or absence of isoproterenol using fura-2/AM. Calcium transients were also measured after the addition of DOX to myocytes pretreated with a calcium antagonist, benidipine. DOX reduced the amplitude, maximum velocity of increase and decrease of calcium transients and prolonged the time course of calcium transients and impaired the beta-adrenoceptor responsiveness of calcium transients in a concentration-dependent manner. The DOX-induced impairment of calcium transients and beta-adrenoceptor responsiveness was improved by 10(-8) mol/L of benidipine. However, these improvements decreased with increasing concentrations of benidipine. DOX impaired both the mobilization and removal of intracellular calcium ions in contraction-relaxation cycles and the response of calcium transients to beta-adrenoceptor stimulation. Appropriate concentration of benidipine ameliorated DOX-induced impairment of calcium dynamics, suggesting that benidipine, a long-acting calcium antagonist, has potential clinical usefulness on DOX-induced abnormal calcium handling.

Elevated extracellular glutamate concentrations increased malondialdehyde production in anesthetized rat brain cortex

Oxidative stress is believed to be involved in the damaging mechanism of excitotoxic insult. Thus, we investigated the effect of elevated extracellular glutamate levels on malondialdehyde production, a common index of lipid peroxidation, in anesthetized rat brain cortex. Elevation of extracellular glutamate levels was achieved either by exogenously perfusing glutamate solutions, or by perfusing L-trans-pyrrolidine-2,4-dicarboxylate (PDC), a competitive inhibitor of glutamate uptake transporter, through an implanted microdialysis probe. Malondialdehyde levels in the microdialysates, which were reacted with thiobarbituric acid, were analyzed by a high performance liquid chromatography system equipped with a fluorescence detector. Perfusion of glutamate (1.5 and 15 mM) resulted in dose-dependent increases in extracellular malondialdehyde production (as high as a 6-fold increase in malondialdehyde production following perfusion of 15 mM glutamate solution). PDC (3.14 and 31.4 mM), not only significantly increased the extracellular glutamate levels in a dose-dependent manner, but also dramatically increased malondialdehyde production (as high as 20-fold increase). These results suggest that excitotoxicity induces oxidative stress in anesthetized rat brain cortex, as evidenced by the glutamate-induced increase in malondialdehyde production.

Inhibition by levetiracetam of a non-GABAA receptor-associated epileptiform effect of bicuculline in rat hippocampus

1. Extracellular recording of field potentials, evoked by commissural stimulation in hippocampal area CA3 of anaesthetized rats, was performed in order to study the mode of action of the novel antiepileptic drug levetiracetam (ucb LO59). 2. The amplitude of orthodromic field population spike (PS2) markedly increased and repetitive population spikes appeared when the recording micropipette contained either bicuculline methiodide (BMI), or the specific GABAA antagonist gabazine (SR-95531). 3. BMI-induced increases in PS2 were reduced in a dose-dependent manner by 1 to 320 mumol kg-1 levetiracetam i.v., with a U-shape dose-response relationship. However, levetiracetam did not reduce the increases in PS2 produced by gabazine. 4. Clonazepam (1 mg kg-1, i.p.), carbamazepine (20 mg kg-1, i.p.) and valproate (200 mg kg-1, i.v.) were ineffective in preventing BMI-induced increases in PS2, while the calcium channel antagonist flunarizine, 50 mumol kg-1, i.p., reduced PS2 increments caused by BMI. The L-type calcium channel blocker nifedipine, 100 mumol kg-1, i.p., was without effect. Similar to levetiracetam, flunarizine did not reduce the increases in PS2 induced by gabazine. 5. These data suggest that the increased excitability of CA3 neurones, caused by BMI administered in situ, involves calcium-dependent processes not associated with blockade of GABAA receptors. The inhibition by levetiracetam of this calcium-dependent effect of BMI might contribute to the antiepileptic effects of the drug.

Na+ and high-voltage-activated Ca2+ channel blocking actions of NS-7, a novel neuroprotective agent, in NG108-15 cells

The actions of a novel neuroprotective compound, 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride (NS-7), on voltage-gated Na+, Ca2+ and K+ channels were investigated in a mouse neuroblastoma and rat glioma hybrid cell line, NG108-15, using a whole-cell voltage clamp technique. NG108-15 cells have a tetrodotoxin-sensitive Na+ channel, three types of Ca2+ channel (L, N and T) and voltage-gated K+ channels, all of which were inhibited by NS-7 in a concentration-dependent manner. However, there was a considerable difference in its potency: the IC50 values for the tetrodotoxin-sensitive Na+ channel, L-type Ca2+ channel and N-type Ca2+ channel were similar (7.8, 4.5 and 7.3 microM, respectively), lower than the IC50 value for the T-type Ca2+ channel (17.1 microM), and much lower than the IC50 value for the voltage-gated K+ channel (160.5 microM). NS-7 altered neither the shape nor the reversal potential of the current-voltage curves for Na+, L-type or N-type Ca2+ channels, although the currents were reduced at every potential tested. These results indicate that NS-7 is a Na+ and high-voltage-activated (L- and N-type) Ca2+ channel blocker, and its channel-blocking properties may contribute to its neuroprotective action.

The effects of SB 206284A, a novel neuronal calcium-channel antagonist, in models of cerebral ischemia

The effects of SB 206284A, 1-[7-(4-benzyloxyphenoxy)heptyl] piperidine hydrochloride, have been investigated in vitro on calcium and sodium currents in rat-cultured dorsal root ganglion (DRG) neurones and potassium-mediated calcium influx in rat synaptosomes. Cardiovascular hemodynamic effects in both anesthetized and conscious rats, and neuroprotective activity in in vivo cerebral ischemia models were also investigated. In the rat DRG cells, SB 206284A caused almost complete block of the sustained inward Ca2+ current (IC50 = 2.4 microM), suggesting that the compound is an effective blocker of slowly inactivating, high-voltage calcium current. SB 206284A reduced locomotor hyperactivity in the gerbil bilateral carotid artery occlusion model without affecting ischemia-induced damage in the hippocampal CA1 region. In the rat middle cerebral artery occlusion model, SB 206284A reduced lesion volume in the posterior forebrain, and in the rat photochemical cortical lesion model, lesion volume was reduced even when treatment was delayed until 4 hours after occlusion. At neuroprotective doses, SB 206284A had no cardiovascular effects. These findings show that SB 206284A is a novel calcium channel antagonist that shows neuroprotective properties.

Ca2+ channel antagonist U-92032 inhibits both T-type Ca2+ channels and Na+ channels in hippocampal CA1 pyramidal neurons

The effects of 7-[[4-[bis(4-fluorophenyl)-methyl]-1-piperazinyl]methyl] -2-[(2-hydroxyethyl)amino] 4-(1-methylethyl)-2,4,6-cycloheptatrien-1-one (U-92032), a newly described Ca2+ channel blocker, on voltage-gated ionic currents were measured. Whole cell voltage-clamp records were obtained from acutely isolated CA1 hippocampal pyramidal neurons from 7- to 14-day-old rats. Dimethyl sulfoxide, at either 0.01% or 0.1%, partially inhibited T-type Ca2+ currents (approximately 20% inhibition) but not high-voltage-activated (HVA) Ca2+ currents. Ethanol (0.2%) did not affect Ca2+ currents. U-92032 selectively inhibited T-type Ca2+ currents (median inhibiting concentration approximately 500 nM). HVA Ca2+ currents were less sensitive, with approximately 75% of the current resistant at 10 microM. Inhibition of Ca2+ currents was reversible. U-92032 inhibited Na+ currents at concentrations similar to those required for T-type currents (> 33% block at 1 microM). Block of Na+ currents took several minutes to develop and was irreversible. Voltage-gated K+ currents were insensitive to U-92032 (1 or 10 microM). These results indicate that U-92032 inhibits both T-type Ca2+ channels and Na+ channels, constraining its utility in certain studies. Among Ca2+ channels, however, U-92032 should prove a useful tool for distinguishing physiological contributions of T-type channels.

Negative chronotropic and inotropic effects of U-92032, a novel T-type Ca2+ channel blocker, on the isolated, blood-perfused dog atrium

We investigated the effects of U-92032 ((7-((bis-4-fluorophenyl) methyl)-1-piperazinyl)-2-2(2-hydroxyethylamino)-4-(1-methylethyl)- 2,4, 6-cycloheptatrien-1-one), a novel T-type Ca2+ channel blocker, on sinus rate and atrial contractile force in the isolated, blood-perfused atrium of the dog. U-92032 (1 to 300 nmol) induced negative chronotropic and inotropic responses in a dose-dependent manner, and the percentage decrease in sinus rate was less than that in atrial contractile force. Atropine did not affect the negative responses to U-92032. These results suggest that U-92032, a T-type Ca2+ channel blocker, simultaneously decreases the sinus rate and atrial force as do L-type Ca2+ channel blockers in the isolated dog atrium.

New drug binding sites in Ca2+ channels

New classes of drugs modifying Ca2+ channel activity have become available, this may enlarge the clinical utilities that have been associated with established Ca2+ channel antagonists such as the dihydropyridines (for example, nifedipine). Two such classes are reviewed by Michael Spedding, Barry Kenny and Pierre Chatelain. Fantofarone is a non-dihydropyridine with a novel site of action in the L-type Ca2+ channel that appears to yield a distinct cardiovascular profile. In contrast, fluspirilene and related Na+ and Ca2+ channel inhibitors have a distinct site of action in Ca2+ channels, which is not specific for one channel type. The utility of Na+ and Ca2+ channel inhibitors in ischaemic stroke is compared with new and more selective Na+ channel inhibitors.