Figure 1.

Receptor exocytosis is mediated by two different modes of vesicular fusion. (A) Dissociated hippocampal cultures (>15 DIV) were transfected with TfR-SEP and imaged under TIRF illumination. (B) Sequential images from the cell in (A) show a single transient exocytotic event. Red and white boxes define a 4 and 16 μm² regions of interest analyzed in (C) (Top). Kymograph obtained from (A) shows multiple exocytic events (yellow arrows). (C) Maximum intensity measurements from (A) depict a rapid increase indicating fusion pore opening and a subsequent decay, indicating cargo release to the plasma membrane. (D) Kymograph depicting a single TfR-SEP persistent event in which receptors remain clustered at their site of insertion. Yellow arrow indicates exocytic event. (E) Maximum intensity measurements from (D) show fusion pore opening and lateral receptor diffusion from the insertion site. (F) Kymograph of a representative SEP-B2AR persistent event. (G) Intensity measurements from (F). (H) SEP-GluR1 persistent insertion event. (I) Kymograph from (H). (J) Proportion of transient vs. persistent events was counted for all the receptors in hippocampal cultures and for TfR-SEP in hippocampal and striatal cultures. Persistent events were 9.8 ± 5.5% from the total of TfR events. B2AR showed 8.5 ± 5.1% and Glur1 7.3 ± 4.8% (n = 7–10 cells) (K) Proportion of TfR-SEP persistent events during neuronal development in vitro.