Barium and calcium stimulate secretion from digitonin-permeabilized bovine adrenal chromaffin cells by similar pathways.
We compared the characteristics of secretion stimulated by EGTA-buffered Ba(2+)- and Ca(2+)-containing solutions in digitonin-permeabilized bovine adrenal chromaffin cells. Half-maximal secretion occurred at approximately 100 microM Ba2+ or 1 microM Ca2+. Ba(2+)-stimulated release was not due to release of sequestered intracellular Ca2+ because at a constant free Ba2+ concentration, increasing unbound EGTA did not diminish the extent of release due to Ba2+. The maximal extents of Ba(2+)- and Ca(2+)-dependent secretion in the absence of MgATP were identical. MgATP enhanced Ba(2+)-induced secretion to a lesser extent than Ca(2+)-induced secretion. Half-maximal concentrations of Ba2+ and Ca2+, when added together to cells, yielded approximately additive amounts of secretion. Maximal concentrations of Ba2+ and Ca2+ when added together to cells for 2 or 15 min were not additive. Tetanus toxin inhibited Ba(2+)- and Ca(2+)-dependent secretion to a similar extent. Ba2+, unlike Ca2+, did not activate polyphosphoinositide-specific phospholipase C. These data indicate that (1) Ba2+ directly stimulates exocytosis, (2) Ba(2+)-induced secretion is stimulated to a lesser extent than Ca(2+)-dependent secretion by MgATP, (3) Ba2+ and Ca2+ use similar pathways to trigger exocytosis, and (4) exocytosis from permeabilized cells does not require activation of polyphosphoinositide-specific phospholipase C.
TerBush
D R
DR
Department of Pharmacology, University of Michigan, Ann Arbor 48109-0626.
Holz
R W
RW
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D004072:Digitonin / Q000493:pharmacokinetics*; D004338:Drug Combinations; D010539:Permeability; D013744:Tetanus Toxin / Q000494:pharmacology
D004338:Drug Combinations; D013744:Tetanus Toxin; D001464:Barium; D000255:Adenosine Triphosphate; D004072:Digitonin; D002118:Calcium