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

Na + ‐selective, double‐barrelled microelectrodes were used to measure intracellular Na + activity (a   i Na ) 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   i Naby 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   i Naincreased by 7 to 25 mM. In contrast to glutamate, an initial decrease of a   i Nawas detected during the action of kainate. N‐methyl‐D‐aspartate (NMDA, 10 −5 –10 −3 M) had no effect of Em and a   i Na . The results indicate that leech glial cells have a kainate‐preferring non‐NMDA glutamate receptor.