Figure 8. Effects of ISP on synchronous and asynchronous GABA release from BCs.

A, stimulation-evoked synchronous IPSCs recorded in a PC in the control solution containing normal [Ca²⁺]_o (top trace), and in a solution in which Ca²⁺ was replaced by equimolar Sr²⁺ (middle trace) and during 20 μm ISP application in the Sr²⁺-containing solution (bottom trace). Three successive eIPSCs were superimposed in each record. B, relative amplitudes of synchronous eIPSCs in control (Ca²⁺) and Sr²⁺-containing (Sr²⁺, 31.0 ± 4%) solutions and during the ISP application in the Sr²⁺-containing solution (Sr²⁺+ ISP, 53.3 ± 8.6%). The IPSC amplitude was expressed as a percentage of that determined in the control Ca²⁺-containing solution. C, time course of ISP-induced enhancement of synchronous eIPSCs in the Sr²⁺-containing solution (n = 11). The amplitude of eIPSC was expressed as a percentage of the control (determined before ISP application). D and E, effects of ISP on asynchronous GABA release. In the Sr²⁺-containing solution, a single stimulation (at arrowhead) induced a marked increase in the frequency of asynchronous IPSCs during the time window of 500 ms (indicated by a horizontal bar and shaded area) (D), and the asynchronous IPSCs were further increased by 20 μm ISP application (E). F, pooled data for increases in the occurrence of asynchronous IPSCs in the Sr²⁺-containing solution and its enhancement by ISP application. Asynchronous IPSCs were recorded as in D and expressed as a frequency difference of events detected between pre- and poststimulus time windows (as in D and E) in the control ACSF (Ca²⁺), and Sr²⁺-containing ACSF (Sr²⁺) and during 20 μm IPS application in Sr²⁺-containing ACSF (Sr²⁺+ ISP) (n = 10 for each condition).