KAINATE GLUTAMATE-INDUCED CHANGES IN INTRACELLULAR CALCIUM AND PH IN LEECH GLIAL-CELLS

KAINATE evokes a non-desensitizing membrane depolarization in neuropile glial cells of the leech Hirudo medicinalis. We measured membrane potential and intracellular pH, pH-i, using double-barrelled pH-sensitive microelectrodes, and intracellular calcium, Ca-i(2+), using the change in fluorescence ratio of intracellularly injected fura-2, in these glial cells in situ. 20-50-mu-M kainate produced a depolarization of 18-28 mV and a decrease of pH-i by 0.27 +/- 0.07 pH units. Ca-i(2+) increased by 306 +/- 128 nM upon kainate, which could be inhibited by the non-NMDA antagonist CNQX. Glutamate (0.1 mM) also produced a fall in pH-i and a rise in Ca-i(2+), which were however, much smaller. Quisqualate and N-methyl-D-aspartate had only small or no effects on membrane potential, pH-i or Ca-i(2+). It is concluded that leech neuropile glial cells have a kainate-type glutamate receptor, which mediate significant transients of intracellular H+ and Ca2+.