FIGURE 1.

Illustration of two UVR release modes: pore flickering fusion versus full collapse fusion and [Ca²⁺] near SV upon different experimental conditions. (A,B) Proposed release mechanisms for multivesicular release: coordinated fusion of multiple vesicles at the same time (A) or homotypic fusion of vesicles prior to release (B) could lead to large compact sEPSCs. (C,D) Proposed release mechanism for univesicular release. The green solid line is a representative non-compact (C) or compact (D) sEPSC. The hypothetical release mode which leads to non-compact and compact sEPSCs is illustrated above, respectively. Pore-flickering fusion means the SV forms an intermediate fusion pore on the membrane and the pore opens and closes with certain frequencies, and in turn different amount of transmitter is released in different time period. Non-compact sEPSCs reflect such irregular transmitter release. On the other hand, full collapse fusion is the classical SV fusion on to cell membrane. (E–G) The red solid line shows [Ca²⁺] level (upper panel) and time course (lower panel) near SV when Ca²⁺ channel opens at 1.3 mM [Ca²⁺]_e. The blue solid line shows [Ca²⁺] level (upper panel) and time course (lower panel) near SV under (E) reduced [Ca²⁺]_e, (F) with isradipine, and (G) with BayK in reduced [Ca²⁺]_e. The [Ca²⁺] upon Ca²⁺ channel opening reaches similar level because the [Ca²⁺]_e is the same, so it creates similar driving force; whereas in reduced [Ca²⁺]_e with and without BayK [blue solid line in panels (E,G)].