Effects of Intravesicular H+ and Extracellular H+ and Zn2+ on Insulin Secretion in Pancreatic Beta Cells*
- From the ‡Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200 and the ¶Comprehensive Tissue Center, Department of Surgery, University of Alberta, Edmonton, Alberta T6H 2R8, Canada
Abstract
The effects of extracellular Zn2+ and pH and intravesicular pH on insulin and 5-hydroxytryptamine (5-HT) secretion from pancreatic beta cells were investigated. Insulin and 5-HT secretion from single cells was detected by amperometry as a series of current spikes corresponding to detection of multimolecular packets secreted by exocytosis. Spike width was used as a measure of the kinetics of clearance from the cell and the area of spikes as a measure of amount released. Changes in extracellular pH from 6.9 to 7.9 caused insulin spikes to become narrower with no change in area, whereas the same treatments had no effect on 5-HT secretion. Treatment of cells with Bafilomycin A1 orN-ethylmaleimide, both of which are expected to increase intravesicular pH by inhibiting V-type H+-ATPase, had no effect on 5-HT secretion but caused insulin spikes to become more narrow. These results indicate that exposure to high pH, whether intravesicular or extracellular, accelerates release of insulin during exocytosis without affecting the amount of insulin released. Increasing extracellular Zn2+ concentration from 0 to 25 μm increased the width and decreased the area of insulin spikes without affecting 5-HT secretion. Zn2+ effects were likely exerted through a common-ion effect on Zn2+-insulin dissociation. It was concluded that intravesicular storage conditions and extracellular ions can affect free insulin concentration in the vicinity of beta cells during secretion.
Footnotes
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↵* This research was supported in part by National Institutes of Health Grant RO1 DK46960-01 from the NIDDK and by the Juvenile Diabetes Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Received support as a Presidential Faculty Fellow and an Alfred P. Sloan Fellow. To whom correspondence should be addressed, at the Department of Chemistry, University of Florida, P. O. Box 117200, Gainesville, FL 32611-7200. Tel.: 352-392-9839; Fax: 352-392-4582; E-mail: rtkenn{at}chem.ufl.edu.
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↵‖ Supported by a postdoctoral fellowship from the Alberta Heritage Foundation for Medical Research.
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↵1 The abbreviation used is: 5-HT, 5-hydroxytryptamine.
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↵2 C. A. Aspinwall, S. A. Brooks, J. R. T. Lakey, and R. T. Kennedy, submitted for publication.
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- Received August 6, 1997.
- Revision received October 3, 1997.
