J. Biol. Chem., Vol. 259, Issue 16, 10118-10123, 08, 1984

Regulation of Ca2+ transport by isolated organelles of a rat insulinoma. Studies with endoplasmic reticulum and secretory granules

M Prentki, D Janjic, TJ Biden, B Blondel and CB Wollheim

The regulation of extramicrosomal Ca2+ concentration maintained by suspensions of rat insulinoma microsomes was studied using Ca2+- selective minielectrodes. The Ca2+-transporting activity was MgATP dependent and correlated with the endoplasmic reticulum marker NADPH- cytochrome c reductase. When incubated in a high KCl medium containing Mg2+ and phosphate, the microsomes lowered [Ca2+] within less than 10 min to around 0.2 microM. They had a high Ca2+-sequestering activity since they were able to take up and retain several small Ca2+ additions. No evidence for a Na+/Ca2+ countertransport was obtained. The accumulated Ca2+ was released by the Ca2+ ionophore A23187 or upon transforming ATP into ADP using glucose plus hexokinase. The addition of ADP, at concentrations present in cells, resulted in a dose- dependent and reversible net Ca2+ efflux from the microsomes until a higher [Ca2+] steady state was reached. This was specific for ADP since GDP, UDP, CDP, IDP, and the nonhydrolyzable analogue methylene-ADP as well as AMP and cAMP did not reproduce the effect. Insulin secretory granules were unable to lower medium [Ca2+] or to take up a pulse addition of Ca2+. However, most of the large granular calcium content was released by A23187. The addition of Na+ and lowering or increasing medium pH by 0.2 pH unit did not induce Ca2+ uptake or efflux from the secretory granules. The results indicate that insulinoma endoplasmic reticulum but not insulin secretory granules may play a critical role in the regulation of cytosolic Ca2+. A variation in cellular ADP content following secretagogue addition might modulate Ca2+ fluxes across the endoplasmic reticulum and contribute in raising cytosolic Ca2+.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				R. Rizzuto and T. Pozzan Microdomains of Intracellular Ca2+: Molecular Determinants and Functional Consequences Physiol Rev, January 1, 2006; 86(1): 369 - 408. [Abstract] [Full Text] [PDF]

				P. Gilon and J.-C. Henquin Mechanisms and Physiological Significance of the Cholinergic Control of Pancreatic {beta}-Cell Function Endocr. Rev., October 1, 2001; 22(5): 565 - 604. [Abstract] [Full Text] [PDF]

				A. Tengholm, B. Hellman, and E. Gylfe Glucose Regulation of Free Ca2+ in the Endoplasmic Reticulum of Mouse Pancreatic Beta Cells J. Biol. Chem., December 24, 1999; 274(52): 36883 - 36890. [Abstract] [Full Text] [PDF]

				G. G. Xu, Z.-y. Gao, P. D. Borge Jr., and B. A. Wolf Insulin Receptor Substrate 1-induced Inhibition of Endoplasmic Reticulum Ca2+ Uptake in beta -Cells. AUTOCRINE REGULATION OF INTRACELLULAR Ca2+ HOMEOSTASIS AND INSULIN SECRETION J. Biol. Chem., June 18, 1999; 274(25): 18067 - 18074. [Abstract] [Full Text] [PDF]

				K. J. Mitchell, P. Pinton, A. Varadi, C. Tacchetti, E. K. Ainscow, T. Pozzan, R. Rizzuto, and G. A. Rutter Dense core secretory vesicles revealed as a dynamic Ca2+ store in neuroendocrine cells with a vesicle-associated membrane protein aequorin chimaera J. Cell Biol., October 1, 2001; 155(1): 41 - 52. [Abstract] [Full Text] [PDF]