Development of depolarization-induced calcium transients in insect glial cells is dependent on the presence of afferent axons

Changes in the intracellular Ca(2+) concentration (Ca(2+)](i)) induced by depolarization have been measured in glial cells acutely isolated from antennal lobes of the moth Manduca sexta at different postembryonic developmental stages. Depolarization of the glial cell membrane was elicited by increasing the external K(+) concentration from 4 to 25 mM. At midstage 5 and earlier stages, less than 20% of the cells responded to 25 mM K(+) (1 min) with a transient increase in Ca(2+)](i) of approximately 40 nM. One day later, at late stage 5, 68% of the cells responded to 25 mM K(+), the amplitude of the Ca(2+)](i) transients averaging 592 nM. At later stages, all cells responded to 25 mM K(+) with Ca(2+)](i) transients with amplitudes not significantly different from those at late stage 5. In stage 6 glial cells isolated from deafferented antennal lobes, i.e., from antennal lobes chronically deprived of olfactory receptor axons, only 30% of the cells responded with Ca(2+)](i) transients. The amplitudes of these Ca(2+)](i) transients averaged 93 nM and were significantly smaller than those in normal stage 6 glial cells. Ca(2+)](i) transients were greatly reduced in Ca(2+)-free, EGTA-buffered saline, and in the presence of the Ca(2+) channel blockers cadmium and verapamil. The results suggest that depolarization of the cell membrane induces Ca(2+) influx through voltage-activated Ca(2+) channels into antennal lobe glial cells. The development of the depolarization-induced Ca(2+) transients is rapid between midstage 5 and stage 6, and depends on the presence of afferent axons from the olfactory receptor cells in the antenna.