Effects of Kainic Acid on Brain Calcium Fluxes Studied In Vivo and In Vitro

Abstract

The effect of in vivo administration of kainic acid into the rabbit hippocampus was studied with brain dialysis and subsequent determination of the Ca²⁺ concentration in the dialysate. When included in the perfusing medium, kainic acid as well as veratridine induced a decrease in extracellular Ca²⁺. The effect of kainic acid (but not of veratridine) was insensitive to tetrodotoxin. In vitro studies revealed no effect of kainic acid on ⁴⁵Ca²⁺ uptake by isolated astrocytes, but showed an enhancement of synaptosomal ⁴⁵Ca²⁺ accumulation. This was, however, only 25% of the stimulatory effect of high K⁺ depolarization. Glutamate activated synaptosomal Ca²⁺ uptake, whereas dihydrokainate had no effect. The up take evoked by kainate and glutamate was independent of the K⁺ level in the medium which indicates the involvement of other than voltage-sensitive Ca²⁺ channels. The results confirm previous findings that kainic acid promotes the uptake of Ca²⁺ in brain cells. Kainate affects Ca²⁺ fluxes pre- and postsynaptically. Presynaptic Ca²⁺ influx may be mediated by chemically gated mechanisms.