Calcium uptake into acini from rat pancreas: Evidence for intracellular ATP-dependent calcium sequestration |
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Authors: | H Wakasugi T Kimura W Haase A Kribben R Kaufmann I Schulz |
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Institution: | (1) Max-Planck-Institut für Biophysik, Kennedyallee 70, 6000 Frankfurt (Main) 70, Germany;(2) Present address: The Third Department of Internal Medicine, Faculty of Medicine, Kyushu University, Maidashi 3-1-1, 812 Fukuoka, Japan;(3) Present address: Institut für Klinische Physiologie der Universität Düsseldorf, Düsseldorf, Germany |
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Abstract: | Summary Intracellular ATP-dependent Ca2+ sequestration mechanisms were studied in isolated dispersed rat pancreatic acini following treatment with saponin or digitonin to disrupt their plasma membranes. In the presence of45Ca2+ concentrations <10–6 mol/liter, addition of 5 mmol/liter ATP caused a rapid increase in45Ca2+ uptake exceeding the control by fivefold. ADP mimicked the ATP effect by 50 to 60%, whereas other nucleotides such as AMP-PNP, AMP-PCP, CTP, UTP, ITP, GTP, cAMP and cGMP did not. Maximal ATP-promoted Ca2+ uptake was obtained at 10–5 mol/liter Ca2+ uptake by mitochondrial inhibitors was dependent on the Ca2+ concentration, indicating the presence of different Ca2+ storage systems. Whereas the apparent half-saturation constant found for mitochondrial Ca2+ uptake was 4.5×10–7 mol/liter, in the presence of antimycin and oligomycin (nonmitochondrial uptake) it was 1.4×10–8 mol/liter. In the absence of Mg2+ both ATP- and ADP-promoted Ca2+ uptake was nearly abolished. The Ca2+ ionophore and mersalyl blocked Ca2+ uptake. Electron microscopy showed electrondense precipitates in the rough endoplasmic reticulum of saponintreated cells in the presence of Ca2+, oxalate and ATP, which were absent in intact cells and in saponin-cells without ATP or pretreated with A23187. The data suggest the presence of mitochondrial and nonmitochondrial ATP-dependent Ca2+ storage systems in pancreatic acini. The latter is likely to be located in the rough endoplasmic reticulum. |
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Keywords: | pancreas Ca2+ pools Ca2+ pump acini saponin secretagogue |
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