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

Abstract

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...

Antiarrhythmic calcium channel blocker verapamil inhibits trek currents in sympathetic neurons

“…It has been suggested that the binding site of verapamil on other potassium channels located intracellularly (Cohen et al, 1987;Rauer and Grissmer, 1999) and that their adhesion causes a collapse of the pore (Baba et al, 2015). However, it is also described that verapamil might exert its blockade by interacting with the extracellular side of these channels (Keith et al, 1994). Our dose-responses curves of verapamil with both the membrane depolarization and I RIL report a Hill coefficient that suggest that this effect happens through a similar mechanism which might require at least two interaction sites acting cooperatively in the channel (Monod et al, 1965;Weiss, 1997).…”

“…This is the case for class IV antiarrhythmic drugs used in pathological conditions such as chronic angina pectoris, cardiac arrhythmias or hypertension (Kato et al, 2004). In fact, the phenylalkylamine verapamil exerts its therapeutic action predominantly on cardiac cells, reducing heart contractility and rate (Cohen et al, 1987), by blocking L-type calcium channels (Keith et al, 1994;Bergson et al, 2011). Notwithstanding, verapamil has also been shown to exert a significant inhibition of T-type calcium channels expressed in both native and heterologous systems (Freeze et al, 2006;Bergson et al, 2011).…”

Efeitos cardiovasculares da peçonha e de um peptídeo isolado da aranha Vitalius dubius (Araneae, Theraphosidae)

“…Hanatoxinas, encontradas na peçonha de G. spatulata inibem canais de potássio do tipo Kv2.1 e Kv4.2 [56], enquanto a omega-grammotoxin SIA (GsTxSIA) bloqueia os canais de cálcio dependentes de voltagem do tipo N, P e Q [47,57].…”