Thiol oxidation by 2,2'-dithiodipyridine causes a reversible increase in cytoplasmic free Ca2+ concentration in pancreatic beta-cells. Role for inositol 1,4,5-trisphosphate-sensitive Ca2+ stores.
2,2'-Dithiodipyridine (2,2'-DTDP), a reactive disulphide that mobilizes Ca2+ from ryanodine-sensitive Ca2+ stores in muscle, induced a biphasic increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells loaded with fura 2. This increase consisted of an early transient followed by a second, slower, rise. The [Ca2+]i transient was dependent on extracellular Ca2+ and disappeared on treatment with nimodipine. The reactive disulphide caused plasma membrane depolarization, as studied by the perforated-patch configuration of the patch-clamp technique. Hence membrane depolarization and opening of the L-type voltage-gated Ca2+ channels were responsible for the first transient in [Ca2+]i. The second slower increase in [Ca2+]i was prolonged but readily reversed by the disulphide-reducing agent 1,4-dithiothreitol. This increase in [Ca2+]i was not decreased by nimodipine or by omission of extracellular Ca2+, but was eliminated when the Ins(1,4,5)P3-sensitive Ca2+ pool was first depleted by carbachol. Ryanodine or its beta-alanyl analogue did not release Ca2+ from intracellular stores, and a high concentration of ryanodine did not inhibit Ca2+ release by 2,2'-DTDP. The disulphide compound suppressed glucose metabolism and decreased the mitochondrial inner-membrane potential. We conclude that thiol oxidation by 2,2'-DTDP affects Ca2+ homeostasis in beta-cells by multiple mechanisms. However, unlike the situation in muscle, in beta-cells 2,2'-DTDP releases Ca2+ from intracellular pools by mechanisms that do not involve activation of ryanodine receptors. Instead, in these cells the Ins(1,4,5)P3-sensitive intracellular Ca2+ store comprises an alternative target for the Ca(2+)-mobilizing action of the reactive disulphide compound.
Islam
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MS
Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, Stockholm, Sweden.
Kindmark
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H
Larsson
O
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Berggren
P O
PO
D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology*; D002469:Cell Separation; D002470:Cell Survival; D003592:Cytophotometry; D003593:Cytoplasm / Q000378:metabolism* / Q000502:physiology; D004220:Disulfides / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D007424:Intracellular Fluid / Q000378:metabolism; D007425:Intracellular Membranes / Q000502:physiology; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials; D051379:Mice; D008820:Mice, Obese; D009249:NADP / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism*
D004220:Disulfides; D013438:Sulfhydryl Compounds; C001105:2,2'-dipyridyl disulfide; D009249:NADP; D015082:2,2'-Dipyridyl; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium