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Quantal analysis of 5-hydroxytryptamine release from mouse pancreatic beta-cells
P A Smith1, P Proks, F M Ashcroft
1University Laboratory of Physiology, Oxford, UK. pas59404@glaxowellcome.co.uk
The Journal of Physiology
|December 22, 1999
Summary
Pancreatic beta-cells secrete hormones based on calcium (Ca2+) levels. This study reveals secretion kinetics and Ca2+ dependence, identifying a readily releasable pool of ~200 vesicles critical for hormone release.
Area of Science:
- Endocrinology
- Cell Biology
- Neuroscience
Background:
- Pancreatic beta-cells are crucial for glucose homeostasis.
- Voltage-gated calcium channels (VGCCs) regulate insulin secretion.
- Understanding the precise kinetics of Ca2+ entry and exocytosis is vital.
Purpose of the Study:
- To investigate the Ca2+ dependence and kinetics of secretion from pancreatic beta-cells.
- To correlate voltage-gated Ca2+ entry with the amount and timing of secretion.
- To characterize the readily releasable pool and unitary vesicle fusion events.
Main Methods:
- Patch-clamp electrophysiology to measure Ca2+ currents.
- Amperometry to detect 5-hydroxytryptamine (5-HT) release.
- Fluorimetry to assess intracellular Ca2+ concentration ([Ca2+]i).
Main Results:
- Secretion magnitude directly mirrored Ca2+ current and entry, indicating voltage dependence.
- A readily releasable pool of ~200 vesicles accounted for secretion under single pulse stimulation.
- Secretion onset showed a variable latency (~50 ms), and rapid decay upon repolarization, despite elevated [Ca2+]i.
- Local Ca2+ concentration at release sites was estimated to be >0.4 µM, peaking at 2-10 µM during secretion.
Conclusions:
- Secretion from pancreatic beta-cells is tightly regulated by voltage-gated Ca2+ entry and local Ca2+ dynamics.
- The kinetics of secretion are rapid and precisely controlled by the readily releasable pool and unitary vesicle fusion.
- These findings provide critical insights into the mechanisms of glucose-stimulated insulin secretion.