Calcium- and barium-dependent exocytosis from the rat insulinoma cell line RINm5F assayed using membrane capacitance measurements and serotonin release

Electrophysiological measurements of cell capacitance (Cm) and biochemical assays of [3H] serotonin ([3H]5-hydroxytryptamine or [3H]5-HT) release were combined to study the control of secretion in rat insulinoma RINm5F cells. Depolarizing pulses produced Cm changes (DeltaCm), indicative of exocytosi...

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Bibliographic Details
Published in:Pflügers Archiv 1996-06, Vol.432 (2), p.258-269
Main Authors: Richmond, J E, Codignola, A, Cooke, I M, Sher, E
Format: Article
Language:English
Subjects:
Animals
Barium - physiology
Cadmium - pharmacology
Calcium - physiology
Electric Conductivity
Electric Stimulation
Endocytosis
Exocytosis
Insulinoma - pathology
Insulinoma - physiopathology
Intracellular Membranes - metabolism
Pancreatic Neoplasms - pathology
Pancreatic Neoplasms - physiopathology
Patch-Clamp Techniques
Rats
Serotonin - metabolism
Tumor Cells, Cultured
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Summary:Electrophysiological measurements of cell capacitance (Cm) and biochemical assays of [3H] serotonin ([3H]5-hydroxytryptamine or [3H]5-HT) release were combined to study the control of secretion in rat insulinoma RINm5F cells. Depolarizing pulses produced Cm changes (DeltaCm), indicative of exocytosis, with the same voltage and Ca2+ dependency as the inward Ca2+ currents (ICa). Ba2+ was able to substitute for Ca2+ in stimulating exocytosis, but not endocytosis. However, both the relative potency and kinetics of Ca2+-versus Ba2+-triggered exocytosis differed significantly. 5-HT synthesis and uptake were demonstrated in RINm5F cells. This allowed the use of [3H]5-HT to study hormone release from cell populations. [3H]5-HT was released in a depolarization-, Ca2+- and time-dependent manner. Ba2+ also substituted for Ca2+ in depolarization-induced [3H]5-HT release. Thapsigargin, used to deplete Ca2+ stores, had no effects on Ca2+-triggered Cm increases, but Ca2+-triggered [3H]5-HT release was abolished. Ba2+-triggered [3H]5-HT release, however, was only slightly affected by Ca2+ store depletion. Ba2+ was found to act directly as a secretagogue of [3H]5-HT in intact cells, but not in Cm measurements of voltage-clamped cells, suggesting that cell depolarization is a prerequisite for this action.
ISSN:0031-6768
1432-2013
DOI:10.1007/s004240050132