Inhibition of K+-evoked [3H]D-aspartate release and neuronal calcium influx by verapamil, diltiazem and dextromethorphan: evidence for non-L/non-N voltage-sensitive calcium channels

1 The modulation of depolarization (4-aminopyridine, 2 mM)-evoked endogenous glutamate release by k-opioid receptor activation and blockade of voltage-dependent Ca 2+ -channels has been investigated in synaptosomes prepared from rat and marmoset striatum. 2 4-Aminopyridine (4-AP)-stimulated, Ca 2+ -dependent glutamate release was inhibited by enadoline, a selective k-opioid receptor agonist, in a concentration-dependent and norbinaltorphimine (nor-BNI, selective k-opioid receptor antagonist)-sensitive manner in rat (IC 50 =4.4+0.4 mM) and marmoset (IC 50 =2.9+0.7 mM) striatal synaptosomes. However, in the marmoset, there was a signi®cant (&23%) nor-BNI-insensitive component. -channels in the marmoset. 6 In conclusion, the results presented suggest that there are species dierences in the control of glutamate release by k-opioid receptors and Ca 2+ -channels.

Section: +supporting

confidence: 82%

Control of glutamate release by calcium channels and κ‐opioid receptors in rodent and primate striatum

Hill¹,

Brotchie²

1999

“…Furthermore, the ability of micromolar concentrations of haloperidol and DTG to inhibit ischaemia-induced release of glutamate from rat hippocampal slices (Lobner & Lipton, 1990) may reflect their blockade of dihydropyridine-resistant Ca2+ channels which participate in neurotransmitter release (see Burke et al, 1993;Luebke et al, 1993;Wheeler et al, 1994). This possibility is supported by the fact that haloperidol, ifenprodil, rimcazole, DXM, carbetapentane and caramiphen are all able to reduce K+-stimulated excitatory amino acid release from hippocampal or striatal slices with micromolar IC50 values approximating those obtained for block of HVA Ca2" channels in the present experiments (Annels et al, 1991;Mangano et al, 1991;Ellis & Davies, 1994). Similarly, the weak IB, blocking action of (+)-3-PPP parallels its low potency as an inhibitor of K+-stimulated glutamate release from rat striatal slices (IC50> 100 gM; Ellis & Davies, 1994).…”

Section: Electrophysiological Studiesmentioning

confidence: 96%

Blockade by sigma site ligands of high voltage‐activated Ca²⁺ channels in rat and mouse cultured hippocampal pyramidal neurones

Church

Fletcher

1995

1 The effects of a series of structurally-dissimilar ai site ligands were examined on high voltage-activated Ca2`channel activity in two preparations of cultured hippocampal pyramidal neurones. 2 In mouse hippocampal neurones under whole-cell voltage-clamp, voltage-activated Ca2`channel currents carried by barium ions (IB.) were reduced with the rank order (IC" values in (18)>opipramol (32)>carbetapentane (40) (42)>caramiphen (47)>dextromethorphan (73). At the highest concentrations tested, the compounds almost abolished IB. in the absence of any other pharmacological agent.3 The current-voltage characteristics of the whole-cell IB. were unaffected by the test compounds. The drug-induced block was rapid in onset and offset, with the exceptions of carbetapentane and caramiphen where full block was achieved only after two to three voltage-activated currents and was associated with an apparent increase in the rate of inactivation of IB.4 In rat hippocampal neurones loaded with the Ca2"-sensitive dye Fura-2, rises in intracellular free Ca2+ concentration evoked by transient exposure to 50 mM K+-containing medium, either in the absence or in the presence of 10 pM nifedipine (to block L-type high voltage-activated Ca2`channels), were also reversibly attenuated by the ai ligands. The rank order potencies for the compounds in these experimental paradigms were similar to that observed for blockade of IB, in the electrophysiological studies. 5These results indicate that, at micromolar concentrations, the compounds tested block multiple subtypes of high voltage-activated Ca2" channels. These actions, which do not appear to be mediated by high-affinity a binding sites, may play a role in some of the functional effects previously described for the compounds.

“…We recently showed that verapamil inhibits K+-evoked [3H]-D-aspartate release from hippocampal brain slices and K+-evoked increases in intracellular calcium in cortical neurones in primary culture (Mangano et al, 1991). The results from this study, as well as earlier studies that found verapamil inhibited K+-evoked synaptosomal 45Ca2" influx (Akerman & Nicholls, 1981;Reynolds et al, 1986;Wei & Chiang, 1986) Cell culture Primary cultures of rat cortical neurones were prepared by a procedure similar to that described by Dichter (1978).…”

Section: Introductionmentioning

confidence: 58%

“…The K+-evoked increase of intracellular calcium in cortical neurones in culture represents a measure of neuronal cell body calcium entry. Inasmuch as these K+-evoked responses are dependent on the presence of extracellular calcium, and inhibited by selective inhibitors of VSCC (Mangano et al, 1991;Mintz et al, 1992;Lampe et al, 1993b;Keith et al, 1994), it is likely that they represent functional responses of neuronal VSCC. Emopamil has been shown to be neuroprotective in a variety of experimental ischaemia models (Nakayama et al, 1989;Bielenberg et al, 1989;Lin et al, 1990;Block et al, 1990;Morikawa et al, 1991;Okiyama et al, 1992;Seega & Elger, 1993 emopamil 'anti-ischaemic' binding site has been discovered that is prevalent in liver but is also found in brain (Zech et al, 1991;Moebius et al, 1993b).…”

Section: Discussionmentioning

confidence: 99%

“…Methods involved in loading cells with fura-2 and estimation of intracellular calcium have previously been described in detail (Mangano et al, 1991) and are similar to those described by others (Murphy et al, 1987;Thayer et al, 1988;Murphy & Miller, 1989). The cells were perfused at a rate of 2 ml min-' (gravity flow) which allowed for a complete solution exchange in the superfusion system within approximately lO s. Where indicated, depolarization-induced calcium influx was produced by changing the perfusion solution from one with low K+ (5.4 mM) to one with high K+ (50 mM).…”

Section: Measurement Of Intracellular Calciummentioning

confidence: 98%

See 1 more Smart Citation

Differential inhibition of neuronal calcium entry and [³H]‐D‐aspartate release by the quaternary derivatives of verapamil and emopamil

Keith

Mangano

DeFeo

et al. 1994

1 Verapamil and emopamil are structurally related phenylalkylamine calcium channel/5-HT2 receptor antagonists that differ in their anti-ischaemic properties in experimental studies. The quaternary ammonium derivatives of these compounds were prepared and tested in assays of neuronal voltagesensitive calcium channel (VSCC) function to determine whether the compounds act at intra-or extracellular sites. 2 The compounds were tested in K+-evoked: (1) rat brain synaptosomal 45Ca2+ influx, (2) IntroductionEmopamil is a phenylalkylamine inhibitor of voltage-sensitive calcium channels (VSCC) and 5-hydroxytryptamine 5-HT2 receptors Szabo & Hofmann, 1989) that exhibits anti-ischaemic properties in a variety of in vivo models (Nakayama et al., 1988;Bielenberg et al., 1989;Lin et al., 1990;Block et al., 1990; Morikawa et al., 1991;Okiyama et al., 1992;Seega & Elger, 1993). Verapamil is chemically similar to emopamil, yet verapamil exhibits considerably less anti-ischaemic efficacy Lantos et al., 1990;Shirakura et al., 1993). It has been proposed that the limited access of verapamil to the central nervous system could account for its inability to exhibit neuroprotective activity (Szabo, 1989;Defeudis, 1989 Bradford, 1986;Affolter & Coronado, 1986;Cohen et al., 1986;. While the quaternary derivative of verapamil has been evaluated in cardiovascular preparations (Cohen et al., 1986;, neither verapamil nor emopamil quaternary derivatives have been evaluated in neuronal preparations. White & Bradford (1986) showed that D890, the quaternary derivative of methoxyverapamil (D600), was considerably less potent in inhibiting veratridine-induced synaptosomal 45Ca2+ influx and glutamate release. These observations suggest that phenylalkylamines inhibit VSCC by gaining access to an intracellular site. A complication, however, of studying veratridine-evoked responses is the finding that D600 inhibits neuronal VSCC and voltage-sensitive sodium channels at comparable concentrations (Pauwels et al., 1990).Although it has been suggested that the anti-ischaemic actions of emopamil are due to activity at neuronal sites (Bielenberg et al., 1989;Block et al., 1990;Matsumoto et al., 1993) Cell culturePrimary cultures of rat cortical neurones were prepared by a procedure similar to that described by Dichter (1978). Briefly, cortices were asceptically dissected from Sprague-Dawley foetal rats (17-19 days gestation). Following incubation with 0.08% trypsin, the tissue was triturated, diluted with minimal essential medium (MEM) supplemented with 10% foetal bovine serum and 10% heat-inactivated horse serum, and plated. Cells were plated in 35 mm plates (Fisher) at a density of 750,000 cells per plate. Each 35 mm plate contained a round 25 mm No. 1 cover glass (Erie Scientific) on which plated cells could attach. Culture plates and cover glasses were precoated by incubating them for 3 h with 0.1 mg ml-' poly-L-lysine in 0.01 M borate buffer, pH 8.4, followed by a wash with distilled water. At all times, cultures were maintained at 37°C in a humidifie...