Regulated Exocytosis and Kiss-and-Run of Synaptic-Like Microvesicles in INS-1 and Primary Rat β-Cells

  1. Patrick E. MacDonald1,
  2. Stefanie Obermüller1,
  3. Jenny Vikman1,
  4. Juris Galvanovskis1,
  5. Patrik Rorsman12 and
  6. Lena Eliasson1
  1. 1Section of Diabetes, Metabolism and Endocrinology, Lund University, Lund, Sweden
  2. 2Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Oxford, U.K
  1. Address correspondence and reprint requests to Dr. Patrick E. MacDonald, Lund University, Molecular and Cellular Physiology, Tornavägen 10, BMC B11, 221 84 Lund, Sweden. E-mail: patrick.macdonald{at}mphy.lu.se

Abstract

We have applied cell-attached capacitance measurements to investigate whether synaptic-like microvesicles (SLMVs) undergo regulated exocytosis in insulinoma and primary pancreatic β-cells. SLMV and large dense-core vesicle (LDCV) exocytosis was increased 1.6- and 2.4-fold upon stimulation with 10 mmol/l glucose in INS-1 cells. Exocytosis of both types of vesicles was coupled to Ca2+ entry through l-type channels. Thirty percent of SLMV exocytosis in INS-1 and rat β-cells was associated with transient capacitance increases consistent with kiss-and-run. Elevation of intracellular cAMP (5 μmol/l forskolin) increased SLMV exocytosis 1.6-fold and lengthened the duration of kiss-and-run events in rat β-cells. Experiments using isolated inside-out patches of INS-1 cells revealed that the readily releasable pool (RRP) of SLMVs preferentially undergoes kiss-and-run exocytosis (67%), is proportionally larger than the LDCV RRP, and is depleted more quickly upon Ca2+ stimulation. We conclude that SLMVs undergo glucose-regulated exocytosis and are capable of high turnover. Following kiss-and-run exocytosis, the SLMV RRP may be reloaded with γ-aminobutyric acid and undergo several cycles of exo- and endocytosis. Our observations support a role for β-cell SLMVs in a synaptic-like function of rapid intra-islet signaling.

Footnotes

    • Accepted December 13, 2004.
    • Received August 18, 2004.
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