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, Ca2+i, using the change in fluorescence ratio of intracellularly injected fura-2, in these glial cells in situ. 20-50 microM kainate produced a depolarization of 18-28 mV and a decrease of pH(i) by 0.27 +/- 0.07 pH units. Ca2+i 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 Ca2+i, which were however, much smaller. Quisqualate and N-methyl-D-aspartate had only small or no effects on membrane potential, pH(i) or Ca2+i. It is concluded that leech neuropile glial cells have a kainate-type glutamate receptor, which mediate significant transients of intracellular H+ and Ca2+.