CA2-CELLS AND NEURONS CAUSED BY PHARMACOLOGICALLY DISTINCT GLUTAMATE RECEPTORS( INFLUX INTO LEECH GLIAL)

The effect of glutamatergic agonists on the intracellular free Ca2+ co ncentration ([Ca2+](i)) of neuropile glial cells and Retzius neurones in intact segmental ganglia of the medicinal leech Hirudo medicinalis was investigated by using iontophoretically injected fura-2. In physio logical Ringer solution the [Ca2+](i) levels of both cell types were a lmost the same (glial cells: 58 +/- 30 nM, n = 51; Retzius neurones: 6 1 +/- 27 nM, n = 64). In both cell types glutamate, kainate, and quisq ualate induced an increase in [Ca2+](i) which was inhibited by 6,7-din itroquinoxaline-2,3-dione (DNQX). This increase was caused by a Ca2+ i nflux from the extracellular space because the response was greatly di minished upon removal of extracellular Ca2+. The glutamate receptors o f neuropile glial cells and Retzius neurones differed with respect to the relative effectiveness of the agonists used, as well as with regar d to the inhibitory strength of DNQX, In Retzius neurones the agonist- induced [Ca2+](i) increase was abolished after replacing extracellular Na+ by organic cations or by mM amounts of Ni2+, whereas in glial cel ls the [Ca2+](i) increase was largely preserved under both conditions. It is concluded that in Retzius neurones the Ca2+ influx is predomina ntly mediated by voltage-dependent Ca2+ channels, whereas in neuropile glial cells the major influx occurs via the ion channels that are ass ociated with the glutamate receptors. (C) 1994 Wiley-Liss, Inc.