(+/-)-kavain inhibits the veratridine- and KCl-induced increase in intracellular Ca2+ and glutamate-release of rat cerebrocortical synaptosomes.
The action of (+/-)-kavain on the veratridine, monensin and KCl-depolarization evoked increase in free cytosolic Ca2+ concentration ([Ca2+]i), and its influence on the release of endogenous glutamate from rat cerebrocortical synaptosomes were investigated. [Ca2+]i was fluorimetrically determined employing FURA as the Ca2+ sensitive fluorophore, and glutamate was detected by a continuous enzyme-linked fluorimetric assay. The incubation of synaptosomes in the presence of (+/-)-kavain up to a concentration of 500 mumol/l affected neither basal [Ca2+]i nor spontaneous release of glutamate, but dose-dependently reduced both veratridine-elevated [Ca2+]i (IC50 = 63.2 mumol/l) and glutamate-release (IC500 = 116.4 mumol/l). The inhibition of these parameters, attained with 500 mumol/l(+/-)-kavain, could be overcome by inducing an artificial Na+ influx, using monensin as a Na+ ionophore, An application of (+/-)-kavain after veratridine caused a decrease in veratridine-elevated [Ca2+]i, which was similar to the action of tetrodotoxin (TTX) with regard to time course, half-life of [Ca2+]i decline and the final steady state level of [Ca2+]i. Concomitantly, veratridine-induced glutamate-release was blocked. The results indicate that specific inhibition of voltage-dependent Na+ channels is a primary target of (+/-)-kavain, thus preventing a [Na+]i provoked increase in [Ca2+]i and glutamate-release. However, pathways related to the elevation of [Ca2+]i by [Na+]i itself, and the processes involved in normalization of elevated [Ca2+]i and glutamate-release downstream to enhanced [Ca2+]i, seems to be unaffected by (+/-)-kavain. Using KCl-depolarized synaptosomes, 400 mumol/l (+/-)-kavain reduced, in analogy to Aga-GI toxin, KCl-evoked [Ca2+]i and diminished the part of glutamate-exocytosis which is related to external Ca2+ to about 75% of control. At a concentration of 150 mumol/l, which is above the IC50 value necessary to block voltage-dependent Na+ channels, (+/-)-kavain affected neither basal nor the KCl-induced increase in [Ca2+]i. These results might suggest that (+/-)-kavain at concentrations sufficient to block Na+ channels completely. moderately inhibits the non-inactivating Ca2+ channels located on mammalian presynaptic nerve endings.
Gleitz
J
J
Institute of Naturheilkunde, University Clinics Ulm, Germany.
Beile
A
A
Peters
T
T
D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D016257:Fura-2; D018698:Glutamic Acid / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008985:Monensin / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology*; D011753:Pyrones / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014701:Veratridine / Q000494:pharmacology*
D014151:Anti-Anxiety Agents; D007476:Ionophores; D011753:Pyrones; D018698:Glutamic Acid; D011189:Potassium Chloride; D014701:Veratridine; D008985:Monensin; D002118:Calcium; D016257:Fura-2; C011889:kavain