Multicore vesicles: Hyperosmolarity and L-DOPA induce homotypic fusion of dense core vesicles

Aim: A fraction of vesicles in cells treated with hypertonic solution exhibit multiple dense cores and this is enhanced by treatment with l-3,4-dihydroxyphenylalanine (l-DOPA). These cells were examined to determine if the multicore vesicles are the product of endocytosis or homotypic fusion. Methods: Electron microscopy was used to determine the number of multicore vesicles and amperometry was used to examine if the multicore vesicles are a competent fraction of the readily releasable pool. Results: In this study, we observed that a substantial portion (15.3%) of large dense core vesicles in PC12 cells contained multiple cores in hypertonic saline loaded with l-DOPA, and amperometric measurements show a bimodal distribution of quantal sizes in treated cells. Conclusions: The results suggest that the multicored vesicles are formed from homotypic fusion of LCDVs prior to exocytosis.