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Influence of cell number on the characteristics and synchrony of Ca 2+ oscillations in clusters of mouse pancreatic islet cells
Author(s) -
Jonkers Françoise C.,
Jonas JeanChristophe,
Gilon Patrick,
Henquin JeanClaude
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.00839.x
Subject(s) - intracellular , biophysics , islet , chemistry , stimulation , cytoplasm , endocrinology , medicine , biology , biochemistry , insulin
1 The cytoplasmic Ca 2+ concentration ([Ca 2+ ] i ) was measured in single cells and cell clusters of different sizes prepared from mouse pancreatic islets. 2 During stimulation with 15 mM glucose, 20 % of isolated cells were inert, whereas 80 % showed [Ca 2+ ] i oscillations of variable amplitude, duration and frequency. Spectral analysis identified a major frequency of 0.14 min −1 and a less prominent one of 0.27 min −1 . 3 In contrast, practically all clusters (2–50 cells) responded to glucose, and no inert cells were identified within the clusters. As compared to single cells, mean [Ca 2+ ] i was more elevated, [Ca 2+ ] i oscillations were more regular and their major frequency was slightly higher (but reached a plateau at ≈0.25 min −1 ). In some cells and clusters, faster oscillations occurred on top of the slow ones, between them or randomly. 4 Image analysis revealed that the regular [Ca 2+ ] i oscillations were well synchronized between all cells of the clusters. Even when the Ca 2+ response was irregular, slow and fast [Ca 2+ ] i oscillations induced by glucose were also synchronous in all cells. 5 In contrast, [Ca 2+ ] i oscillations resulting from mobilization of intracellular Ca 2+ by acetylcholine were restricted to certain cells only and were not synchronized. 6 Heptanol and 18α‐glycyrrhetinic acid, two agents widely used to block gap junctions, altered glucose‐induced Ca 2+ oscillations, but control experiments showed that they also exerted effects other than a selective uncoupling of the cells. 7 The results support theoretical models predicting an increased regularity of glucose‐dependent oscillatory events in clusters as compared to isolated islet cells, but contradict the proposal that the frequency of the oscillations increases with the number of coupled cells. Islet cell clusters function better as electrical than biochemical syncytia. This may explain the co‐ordination of [Ca 2+ ] i oscillations driven by depolarization‐dependent Ca 2+ influx during glucose stimulation.