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Bidirectional Insulin Granule Turnover in the Submembrane Space During K + Depolarization‐Induced Secretion
Author(s) -
Hatlapatka Kathrin,
Matz Magnus,
Schumacher Kirstin,
Baumann Knut,
Rustenbeck Ingo
Publication year - 2011
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1111/j.1600-0854.2011.01231.x
Subject(s) - depolarization , biology , granule (geology) , secretion , microbiology and biotechnology , biophysics , insulin , cell fractionation , endocrinology , medicine , biochemistry , membrane , paleontology
Like primary mouse islets, MIN6 pseudoislets responded to the depolarization by 40 m m KCl and the resulting increase in the free cytosolic Ca 2+ concentration ([Ca 2+ ] i ) with a massive increase in insulin secretion, whereas 15 m m KCl had little effect in spite of a clear increase in [Ca 2+ ] i . Analysis of insulin‐enhanced green fluorescent protein (EGFP)‐labeled granules in MIN6 cells by total internal reflection fluorescence (TIRF) microscopy showed that 40 m m KCl increased the number of short‐term resident granules (<1 second presence in the submembrane space), while the total granule number and the number of long‐term resident granules decreased. The rates of granule arrival at and departure from the submembrane space changed in parallel and were two orders of magnitude higher than the release rates, suggesting a back‐and‐forth movement of the granules as the primary determinant of the submembrane granule number. The effect of 15 m m KCl resembled that of 40 m m but did not achieve significance. Both 15 and 40 m m KCl evoked a [Ca 2+ ] i increase, which was antagonized by 10 µ m nifedipine. Nifedipine also antagonized the effect on secretion and on granule number and mobility. In conclusion, during KCl depolarization L‐type Ca 2+ channels seem to regulate two processes, insulin granule turnover in the submembrane space and granule exocytosis.