title: Silence of synaptotagmin I in INS-1 cells inhibits fast exocytosis and fast endocytosis.
abstract: Synaptotagmin I (Syt I) is a Ca(2+) sensor for triggering fast synchronized release of neurotransmitters. However, controversy remains whether Syt I is also obligatory for the exocytosis and endocytosis of larger dense core vesicles (LDCVs) in endocrine cells. In this study, we used a short hairpin RNA (shRNA) to silence the expression of Syt I and investigated the roles of Syt I on exocytosis and endocytosis in INS-1 cells. Our results demonstrated that expression of Syt I is remarkably reduced by the Syt I gene targeting shRNA. Using high-time resolution capacitance measurement, we found that the silence of Syt I decreased the calcium sensitivity of fusion of insulin granules and therefore reduced the exocytotic burst triggered by step-like [Ca(2+)](i) elevation. In addition, the occurrence frequency and amplitude of fast endocytosis were remarkably reduced in the silenced cells. We conclude that Syt I not only participates in the Ca(2+)-sensing of LDCV fusion with plasmalemma, but also plays a crucial role in fast endocytosis in INS-1 cells.
authors.affiliation: Institute of Biophysics and Biochemistry, HuaZhong University of Science and Technology, Wuhan, PR China.
authors.forename: Xiong
authors.initials: X
authors.lastname: Xiong
authors.forename: Ke-Ming
authors.initials: KM
authors.lastname: Zhou
authors.forename: Zheng-Xing
authors.initials: ZX
authors.lastname: Wu
authors.forename: Tao
authors.initials: T
authors.lastname: Xu
mesh_terms: D000818:Animals; D002460:Cell Line; D004705:Endocytosis / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D020868:Gene Silencing; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism*; D050863:Synaptotagmin I / Q000235:genetics* / Q000378:metabolism*
chemical_list: D007328:Insulin; D050863:Synaptotagmin I