Abstract
Electrothermal atomic absorption spectroscopy was employed for measuring barium in β-cell-rich pancreatic islets microdissected from
ob/ob-mice. Both the uptake and efflux of barium displayed two distinct phases. There was a 4-fold accumulation of barium into intracellular stores when its extracellular concentration was 0.26 mM. Unlike divalent cations with more extensive intracellular accumulation, the washout of Ba
2+ was not inhibited by
d-glucose. Ba
2+ served as a substitute for Ca
2+ both in maintaining the glucose metabolism after removal of extracellular Ca
2+ and making it possible for glucose to stimulate insulin release. Furthermore, Ba
2+ elicited insulin release in the absence of glucose and other secretagogues. The latter effect was reversible and was markedly potentiated under conditions known to increase the β-cell content of cyclic AMP. It is likely that the observed actions of Ba
2+ are mediated by Ca
2+, since Ca
2+-dependent regulatory proteins, such as calmodulin, apparently cannot bind Ba
2+ specifically.
