Anticonvulsive action of (±)-kavain estimated from its properties on stimulated synaptosomes and Na + channel receptor sites

• Published in: European journal of pharmacology Vol. 315; no. 1; pp. 89 - 97
• Main Authors: Gleitz, Johannes, Friese, Jutta, Beile, Anne, Ameri, Angela, Peters, Thies
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 07-11-1996; Elsevier
• Subjects: 4-Aminopyridine - administration & dosage; Animals; Anticonvulsants - metabolism; Anticonvulsants - pharmacology; Batrachotoxins - metabolism; Biological and medical sciences; Calcium - metabolism; Cerebral Cortex - drug effects; Cerebral Cortex - metabolism; Dose-Response Relationship, Drug; Epilepsy; General pharmacology; Glutamic Acid - metabolism; Kava pyrone; Male; Medical sciences; Na + channel; Pharmacognosy. Homeopathy. Health food; Pharmacology. Drug treatments; Piper methysticum; Pyrones - metabolism; Pyrones - pharmacology; Rats; Rats, Wistar; Saxitoxin - metabolism; Sodium - metabolism; Sodium Channels - drug effects; Sodium Channels - metabolism; Synaptosome; Synaptosomes - drug effects; Synaptosomes - metabolism; Pacific Ocean Islands; Synaptosome; Kava pyrone; Piper methysticum; Epilepsy; Na + channel; Rat; Pharmacognosy; Rodentia; Piperaceae; Anticonvulsant; Ionic channel; In vitro; Vertebrata; Mammalia; Folk medicine; Dicotyledones; Animal; Angiospermae; Plant origin; Sodium ion; Spermatophyta; Mechanism of action
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/S0014-2999(96)00550-X

Kava pyrones are constituents of the intoxicating pepper (
Piper methysticum Forst.), which has been shown to be anticonvulsive. The question of how the excitability of neurons is affected was investigated by determining the interaction of (±)-kavain with epitopes (site 1, site 2) of voltage-dependent Na
+ channels and the action of (±)-kavain on 4-aminopyridine-stimulated synaptosomes as model of repetitive firing neurons. [
3H]Saxitoxin and [
3H]batrachotoxin were used for radioligand-binding assays performed with synaptosomal membranes. Glutamate released from 4-aminopyridine-stimulated cerebrocortical synaptosomes and the cytosolic concentrations of Na
+ and Ca
2+ ([Na
+]
i, [Ca
2+]
i) were detected fluorometrically by using an enzyme-linked assay, sodium-binding benzofuranisophthalate (SBFI) and Fura-2, respectively. (±)-Kavain failed to compete with [
3H]saxitoxin up to 400 μmol/l but dose-dependently suppressed binding of [
3H]batrachotoxin with an IC
50 value of 88 μmol/l (
K
i = 72
μmol/l) although displacement of [
3H]batrachotoxin was restricted to 33% of control at 400 μmol/l (±)-kavain. In stimulated synaptosomes, 5 mmol/1 4-aminopyridine provoked an increase in [Na
+]
i and [Ca
2+]
i by 9 mmol/l Na
+ and 235 nmol/l Ca
2+. Comparable to the reduction in [
3H]batrachotoxin binding, 400 μmol/l (±)-kavain suppressed the increase in [Na
+]
i and [Ca
2+]
i to 38 and 29% of control, respectively. Consistent with the increase in [Na
+]
i and [Ca
2+]
i, 5 mmol/l 4-aminopyridine provoked glutamate release (rate: 38 pmol/s∗mg protein) which was dose-dependently diminished to 60% of control by 400 μmol/l (±)-kavain. KCl depolarization (40 mmol/l) provoked an increase in [Ca
2+]
i and glutamate release almost identical to the responses elicited by 4-aminopyridine but 400 μmol/l (±)-kavain suppressed only the rate of glutamate release by 9% of control. The data suggest an interaction of (±)-kavain with voltage-dependent Na
+ and Ca
2+ channels, thereby suppressing the 4-aminopyridine-induced increase in [Na
+]
i, [Ca
2+]
i and the release of endogenous glutamate.