Figure 1.

Passive astrocytes do not express functional voltage-gated calcium channels. (A) Astrocytes in stratum radiatum of acute hippocampal slices were patch-clamped with a small pipette tip (7–9 MΩ) in order to limit dialysis of the pipette contents during the recording. Included in the pipette was 150 μM of the cell impermeant Ca²⁺ indicator Oregon Green BAPTA-1 (OGB-1). (B) Passive mature astrocytes were characterized by the absence of voltage-gated currents evoked by a voltage-step protocol (−180 to +80 mV in 20 mV increments). (C) In 6/10 astrocytes from 10 slices, despite whole-cell voltage clamp the astrocytes exhibited spontaneous Ca²⁺ elevations (arrows) and evoked Ca²⁺ responses to an agonist cocktail consisting of 10 μM each of the G_q GPCR agonists histamine, carbachol, and ATP. However, strong depolarizing trains (−90 to 0 mV at 1 Hz for 10 or 50 s) through the patch pipette did not produce any increases in fluorescence, indicating a lack of voltage-gated Ca²⁺ channels in astrocytes. The remaining 4/10 astrocytes did not respond to depolarization or agonist cocktail with Ca²⁺ elevations, but did respond to agonist cocktail after pipette removal. This is presumably an effect of dialysis of the cell by the whole-cell recording pipette.