Glutamate and kainate increase intracellular sodium activity in leech neuropile glial cells

Abstract

Na⁺‐selective, double‐barrelled microelectrodes were used to measure intracellular Na⁺ activity (a) and membrane potential (Em) in neuropile glial cells of isolated segmental ganglia in the leech Hirudo medicinalis. Bath application of glutamate (10⁻³ M) resulted in membrane depolarizations of about 5 mV and a concomitant increase of a by between 2 and 10 mM. Kainate (10⁻⁴ M) elicited depolarizations of up to 40 mV amplitude followed by a prominent afterhyperpolarization. During kainate, a increased by 7 to 25 mM. In contrast to glutamate, an initial decrease of a was detected during the action of kainate. N‐methyl‐D‐aspartate (NMDA, 10⁻⁵–10⁻³M) had no effect of Em and a. The results indicate that leech glial cells have a kainate‐preferring non‐NMDA glutamate receptor.