ISSN:
1432-1912
Keywords:
Daurisoline
;
P-type Ca2+ channels
;
Amino acid release
;
Monoamine release
;
Acetylcholine release
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The alkaloid and medicinal herb constituent, R,R-(−)-daurisoline, was originally reported to be a N-type Ca2+ channel blocker, but newer evidence indicates that it is a blocker of P-type Ca2+ channels. To clarify its specificity with respect to N- and P-channels, we compared its effects on the electrically induced release of endogenous glutamate, 3H-GABA and 3H-noradrenaline, from brain slices with those of ω-agatoxin IVA and ω-conotoxin GVIA. Like ω-agatoxin IVA (but with about 1000-fold lower potency), and unlike ω-conotoxin GVIA, R,R-(−)-daurisoline inhibited the release of 3H-GABA and glutamate, with IC50 values of 8 and 18 μM. However, inhibition particularly of 3H-GABA release was more complete than by ω-agatoxin IVA, indicating interaction with one or more additional voltage-sensitive Ca2+ channels, possibly the Q-type. Its potency to inhibit glutamate release elicited either electrically, by veratrine or by high concentrations of K+ was similar, in contrast to sodium channel blockkes. The effects of R,R-(−)-daurisoline on the release of 3H-noradrenaline, 3H-dopamine and 3H-acetylcholine were in agreement with previous knowledge from experiments with ω-agatoxin IVA suggesting an involvement of P-channels. A weak inhibition of 3H-noradrenaline release at 10 μM, similar to that by ω-agatoxin IVA at 0.03 μM, was occluded by α2-antagonistic properties and could be unmasked in presence of rauwolscine. At 10 μM, it also inhibited electrically evoked 3H-dopamine and 3H-5-hydroxytryptamine release and caused a marked spontaneous release of all three monoamines in a reserpine-like manner. Spontaneous and evoked release of 3H-acetylcholine was inhibited by about 25% at 10 μM. In radioligand binding studies, R,R-(−)-daurisoline interacted with α1 and α2-adrenoceptors, 5-HT2 and muscarinic cholinergic receptors with IC50 values close to 1 μM, and with μ opiate receptors even with 0.18 μM. Atropine reduced the weak inhibitory effect of R,R-(−)-daurisoline on 3H-acetylcholine release somewhat, suggesting that it was brought about by both P channel blockade and cholinergic agonist activity. The effect on 3H-GABA release was unaffected by naloxone, indicating that the interaction of R,R-(−)-daurisoline with μ opiate receptors is antagonistic. The pattern of effects on neurotransmitter release observed with R,R-(−)-daurisoline resembles that of ω-agatoxin IVA and supports previous electrophysiological data suggesting that the compound blocks P-type voltage-sensitive Ca2+ channels. However, the more complete blockade of amino acid release by R,R-(−)-daurisoline suggests interaction with additional Ca+ channel subtypes. Although it does also possess other pharmacological properties, we think that the compound is suitable to test whether blockade of glutamate release via voltage-sensitive Ca2+ channels is a viable concept to obtain novel neuroprotective and/or anticonvulsant compounds.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00171327
Permalink
