Effects of Monovalent and Divalent Cations on Ca2+ Fluxes Across Chromaffin Secretory Membrane Vesicles
Article first published online: 5 OCT 2006
Journal of Neurochemistry
Volume 41, Issue 5, pages 1269–1276, May 1983
How to Cite
Krieger-Brauer, H. I. and Gratzl, M. (1983), Effects of Monovalent and Divalent Cations on Ca2+ Fluxes Across Chromaffin Secretory Membrane Vesicles. Journal of Neurochemistry, 41: 1269–1276. doi: 10.1111/j.1471-4159.1983.tb00821.x
- Issue published online: 5 OCT 2006
- Article first published online: 5 OCT 2006
- Received February 7, 1983; accepted April 19, 1983.
- Secretory vesicle;
- Na+/Ca2+ exchange;
- Ca2+/Ca2+ exchange;
- Bovine adrenal medulla
Abstract: Bovine chromaffin secretory vesicle ghosts loaded with Na+ were found to take up Ca2+ when incubated in K+ media or in sucrose media containing micromolar concentrations of free Ca2+. Li+- or choline+loaded ghosts did not take up Ca2+. The Ca2+ accumulated by Na+-loaded ghosts could be released by the Ca2+ ionophore A23187, but not by EGTA. Ca2+ uptake was inhibited by external Sr2+, Na +, Li +, or choline +. All the 45Ca2+ accumulated by Na+-dependent Ca2+ uptake could be released by external Na +, indicating that both Ca2+ influx and efflux occur in a Na+-dependent manner. Na + -dependent Ca2+ uptake and release were only slightly inhibited by Mg2+. In the presence of the Na+ ionophore Monensin the Ca2+ uptake by Na +-loaded ghosts was reduced. Ca2+ sequestered by the Na+-dependent mechanism could also be released by external Ca2+ or Sr2+ but not by Mg2+, indicating the presence of a Ca2+/Ca2+ exchange activity in secretory membrane vesicles. This Ca2+/Ca2+ exchange system is inhibited by Mg2+, but not by Sr2+. The Na + -dependent Ca2+ uptake system in the presence of Mg2+ is a saturable process with an apparent Km of 0.28 μM and a Vmax= 14.5 nmol min−1 mg protein−1. Ruthenium red inhibited neither the Na+/Ca2+ nor the Ca2+/Ca2+ exchange, even at high concentrations.