Figure 3. Bradykinin-induced anion currents in mouse astrocytes.

A, representative whole-cell anion currents activated by 1 μm bradykinin (BK) before and during application of 100 μm phloretin. Alternating step pulses of ±40 mV (0.5 s duration, every 5 s) or step pulses from −100 to +100 mV in 20 mV increments with a pre-pulse (0.1 s duration) to −100 mV and a post-pulse (0.1 s duration) to −100 mV (at a and b) were applied from a holding potential of 0 mV. a and b, expanded traces of current responses to step pulses before (a) and after (b) application of phloretin. Arrowheads: the zero-current level. B, instantaneous current–voltage relationships measured during BK application in the absence (Control, open circles) and presence of 100 μm phloretin (filled circles) or 10 μm DCPIB (filled squares). Instantaneous currents were measured 25–30 ms after the onset of the test pulses. The current density was evaluated by dividing the current by the cell capacitance (59.2 ± 3.8 pF, n= 33). Phloretin and DCPIB significantly inhibited bradykinin-activated anion currents at all the voltages tested (except for 0 mV). C and D, sensitivity of bradykinin-induced currents recorded at +100 mV (C) and −100 mV (D) to bradykinin receptor antagonists, anion channel blockers (phloretin, DCPIB and DIDS), cytosolic ATP removal (>15 min equilibration with ATP-free pipette solution) and osmotic cell shrinkage induced by a hypertonic challenge (350 mosmol (kg H₂O)⁻¹, P < 0.001), but not to a maxi-anion channel blocker (gadolinium, P > 0.1). The percentage inhibition was calculated from the bradykinin-induced peak currents recorded at ±100 mV from astrocytes under control (isotonic, ATP-containing, and blocker-free) conditions (n= 5) and the cells under test conditions. The concentrations of drugs are the same as those in Fig. 2.