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Pancreastatin inhibits insulin secretion in RINm5F cells through obstruction of G-protein mediated, calcium-directed
Z I Hertelendy1, D G Patel, J J Knittel
1Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, OH 45267-0004, USA.
Abstract:
To elucidate the regulatory pathway through which pancreastatin inhibits insulin secretion, RINm5F insulinoma cells were challenged with physiological and pharmacological probes known to stimulate insulin release through different mechanisms. Utilizing the electrophysiological technique of capacitance measurements as a correlate to exocytosis, pancreastatin was found to significantly diminish maximum capacitance changes evoked by glyceraldehyde, an effect which was attenuated in pertussis toxin-treated cells. In static incubations of this cell line, pancreastatin significantly inhibited insulin secretion stimulated by glyceraldehyde, carbachol and A23187, secretagogues known to directly elevate beta-cell cytosolic Ca2+. This peptide also inhibited insulin secretion stimulated by phorbol myristate acetate (PMA), but only at incubation times < or = 15 min. It was without effect on insulin secretion stimulated by mastoparan and longer incubations (30 min) with PMA, where the secretory mechanisms are not necessarily Ca(2+)-dependent. Additionally, pancreastatin had no effect on carbachol-generated inositol phosphate accumulation but inhibited simultaneously stimulated insulin secretion. All inhibitory effects of pancreastatin were pertussis toxin sensitive. These results suggest that pancreastatin inhibits insulin secretion in RINm5F cells through a G-protein regulated mechanism at a control point involved in the Ca(2+)-directed exocytotic machinery, a feature shared by other physiologic inhibitors of insulin secretion.
Insights
Pancreastatin inhibits insulin secretion by targeting the calcium-dependent exocytosis pathway in pancreatic beta cells. This inhibition is mediated by a pertussis toxin-sensitive G-protein signaling mechanism.
Area of Science:
- Endocrinology
- Cell Biology
- Molecular Biology
Background:
- Pancreastatin is a peptide hormone that regulates glucose homeostasis.
- The precise mechanism by which pancreastatin inhibits insulin secretion is not fully understood.
- Understanding this mechanism is crucial for developing new diabetes therapies.
Purpose of the Study:
- To investigate the regulatory pathway of pancreastatin-induced inhibition of insulin secretion.
- To identify the specific cellular targets and signaling cascades involved.
Main Methods:
- Utilized RINm5F insulinoma cells.
- Employed electrophysiological capacitance measurements to assess exocytosis.
- Stimulated insulin secretion using various agents like glyceraldehyde, carbachol, A23187, and phorbol myristate acetate (PMA).
- Assessed the role of G-proteins using pertussis toxin treatment.
- Measured inositol phosphate accumulation.
Main Results:
- Pancreastatin significantly reduced exocytosis and insulin secretion stimulated by calcium-dependent secretagogues.
- These inhibitory effects were attenuated in pertussis toxin-treated cells, indicating G-protein involvement.
- Pancreastatin inhibited insulin secretion stimulated by PMA at early time points (< or = 15 min) but not later.
- No effect on inositol phosphate accumulation was observed, suggesting the mechanism acts downstream of initial signaling.
- All inhibitory effects were sensitive to pertussis toxin.
Conclusions:
- Pancreastatin inhibits insulin secretion in RINm5F cells via a G-protein regulated pathway.
- The mechanism targets the calcium-directed exocytotic machinery.
- This finding aligns with other known physiological inhibitors of insulin secretion.