Effects of K+-induced depolarization and purinergic receptor activation on elemental content in insulin-producing RINm5F-cells

• X-ray microanalysis was used to detect elemental changes in the insulin-producing tumor cell-lineRINm5F. To improve discrimination between mobile ions and ions bound to macromolecules a new approach was employed, consisting of multivariate statistical analysis of correlations between the concentrations of Na, Mg, P, S, CI, K, and Ca. RINm5F cells, cultured an Formvar-coated titanium grids, were stimulated with high K+ or ATP, that are both known to stimulate insulin release. The buffers used contained Ca2+ or one of the Ca2+-analogues Sr2+ and Ba2+, to represent Ca2+ uptake inresponse to stimulation. After stimulation the cells were shock-frozen and freeze-dried overnight. Incubation for 10-20 seconds in a Ca2+-containing buffer did not significantly affect elementalcomposition, whereas cellular Mg, P and K decreased in a Sr2+-containing buffer. Depolarization with high K+ concentration caused an increase in the cellular Na content, both in Ca2+- and Sr2+-containing buffers, but not in the buffer where Ca2+ had been replaced by Ba2+. X-ray microanalysis is useful for detection of elemental changes subsequent to stimulation of cultured cells. Moreover, multivariate statistical analysis strengthens the idea that stimulation of RINm5F cells causes redistribution of ions possibly due to changes in the state of binding of some elements to cellular proteins.

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