Ca²⁺ influx into leech glial cells and neurones caused by pharmacologically distinct glutamate receptors

Abstract

The effect of glutamatergic agonists on the intracellular free Ca2+ concentration ([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 physiological Ringer solution the [Ca2+]i levels of both cell types were almost the same (glial cells: 58 +/- 30 nM, n = 51; Retzius neurones: 61 +/- 27 nM, n = 64). In both cell types glutamate, kainate, and quisqualate induced an increase in [Ca2+]i which was inhibited by 6,7-dinitroquinoxaline-2,3-dione (DNQX). This increase was caused by a Ca2+ influx from the extracellular space because the response was greatly diminished upon removal of extracellular Ca2+. The glutamate receptors of neuropile glial cells and Retzius neurones differed with respect to the relative effectiveness of the agonists used, as well as with regard 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 cells the [Ca2+]i increase was largely preserved under both conditions. It is concluded that in Retzius neurones the Ca2+ influx is predominantly mediated by voltage-dependent Ca2+ channels, whereas in neuropile glial cells the major influx occurs via the ion channels that are associated with the glutamate receptors.

Ca2+ influx into identified leech neurons induced by 5‐hydroxytryptamine

“…1 (Dierkes et al, 1997b;Lohr et al, 2001). 3) In general, glutamate receptors mediating synaptic transmission in the leech CNS are Ca 2ϩ -impermeable (Dierkes et al, 1996;Hochstrate and Schlue, 1994;Löhrke and Deitmer, 1996).…”

Ionic mechanism of ouabain-induced swelling of leech Retzius neurons

“…The experimental procedures and the technical equipment have been described previously in detail [22,23]. In short, the cells were iontophoretically loaded with the dye by using conventional microelectrodes, the tip of which was filled with an aqueous solution of the pentapotassium salt of Fura-2 (50-100 mM; 10-20 nA for 60 s).…”

Effects of ATP and derivatives on neuropile glial cells of the leech central nervous system

“…A possible artifact due to spontaneous Ca 2ϩ oscillations seems unlikely to be the cause for the ATP-induced Ca 2ϩ increase observed in Ca 2ϩ -free solutions, because in all experiments the second Ca 2ϩ peak was clearly correlated to the ATP administration. The fact that the [Ca 2ϩ ] i base level is not reduced upon removal of extracellular Ca 2ϩ has been observed previously Hochstrate and Schlue, 1994), but no sufficient explanation has yet been proposed. Plotted is the Fura-2 fluorescence ratio (F 340 /F 380 ) measured at excitation wavelengths of 340 nm and 380 nm.…”