Ca2+ channel-mediated currents in retinal glial (Muller) cells of the toad(Bufo marinus)

Whole-cell voltage-clamp recordings were used to detect voltage-gated Ca2channels in freshly isolated retinal glial (Muller) cells of the toad (Bufo marinus). Using Ca2+ ions (2 mM) as charge carriers (in the presence of 1 mM Mg2+), no inwardly directed currents could be observed during the applic ation of depolarizing voltage steps. However, after omitting the: divalent cations from the bath solution, large-amplitude inwardly directed currents were evoked that were carried by Na+ ions, and were mediated by at least tw o different kinds of Ca2+ channels, transient low voltage-activated (LVA) c hannels and sustained high voltage-activated (HVA) channels. While the LVA currents activated at potentials positive to -90 mV and peaked at -40 mV, t he HVA currents activated positive to -60 mV and peaked at -20 mV. It is co ncluded that Muller glial cells of the toad express distinct types of volta ge-gated Ca2+ channels that may be activated, under certain conditions, dos e to physiological membrane potentials. (C) 2000 Elsevier Science Ireland L td. All rights reserved.