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 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.
Richmond
J E
JE
Békésy Laboratory of Neurobiology, University of Hawaii, Honolulu, Hawaii, USA.
Codignola
A
A
Cooke
I M
IM
Sher
E
E
D000818:Animals; D001464:Barium / Q000502:physiology*; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D004553:Electric Conductivity; D004558:Electric Stimulation; D004705:Endocytosis; D005089:Exocytosis; D007340:Insulinoma / Q000473:pathology / Q000503:physiopathology*; D007425:Intracellular Membranes / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000473:pathology / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D051381:Rats; D012701:Serotonin / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D002104:Cadmium; D001464:Barium; D012701:Serotonin; D002118:Calcium