Figure 5. 0.5 Hz sAPs increase exocytosis in the absence of Ca²⁺ influx.

A, experiment schematic. ACCs were patched in normal external solution (with Ca²⁺). The whole cell configuration was achieved after the chamber was rapidly exchanged (within 3 min) with 30–40 ml of Ca²⁺-free external solution. The ACC and internal solution were allowed to equilibrate for 5 min and then 2 min amperometric recordings were performed, first in the absence of stimulation, followed by simultaneous stimulation with sAPs at 0.5 Hz. B, representative traces of amperometric events from two cells unstimulated (left) and then during stimulation with sAPs at 0.5 Hz for 120 s (right). The upper and lower sets of traces are from two separate cells. On the right the 120 s traces were divided into 60 segments of 2 s and overlaid, such that the onset of each trace is synchronized with the sAP as shown in the schematic above, i.e. 60 segments of 2 s where each starts at the initiation of an sAP. On the left the traces are similarly accumulated but in the absence of stimulation. C, data from B binned in the same fashion and according to the same conventions as in Fig.2B. Amperometric events in each 2 s segment were binned into 200 ms increments according to their latency from the last sAP during 0.5 Hz stimulation. Right, the first bin (coloured overlay) contains events within 200 ms of an sAP, which are considered as synchronized exocytosis (n = 22 cells, 1320 sAPs, 412 events). Left, control, pre-stimulation data from the same cells from each 2 s sweep were binned into 200 ms intervals beginning at the onset of each sweep, with no sAPs (177 events). D, effect of 0.5 Hz stimulation on asynchronous vs. synchronous release frequency. Events within 200 ms of an sAP increase from 0.047 ± 0.02 s⁻¹ (Pre) to 0.176 ± 0.05 s⁻¹ (P = 0.043); events after 200 ms of an sAP increase to 0.169 ± 0.05 s⁻¹ (P = 0.042) (Bonferroni-corrected, paired sample t tests).