[Ca(2+)](i)- and insulin-stimulating effect of the non-membranepermeable phosphatase-inhibitor microcystin-LR in intact insulin-secreting cells (RINm5F).
1. Microcystin-LR, a specific and effective inhibitor of serine/threonine phosphatases type 1/2A which does not permeate cells, was used to distinguish intracellular and extracellular effects of phosphatase inhibitors on insulin secretion by RINm5F cells. 2. Incubation of intact RINm5F cells with microcystin-LR (0.1 - 2 microM) almost doubled basal insulin release at 3 mM glucose but left maximal insulin release induced by KCl (30 mM) unaffected. 3. In parallel, there was an increase in cytosolic Ca(2+) by up to half maximum, which could be suppressed by the Ca(2+)-channel blocker D600. 4. In contrast, microcystin-LR incubation of intact cells did not affect phosphatase activity but significantly reduced phosphatase activity when used in cellular fractions. 5. From these data we conclude that microcystin-LR could affect Ca(2+)-channels and insulin release by inhibiting an extracellular phosphatase-like activity.
Leiers
T
T
Department of Pharmacology, Institute of Pharmaceutical Sciences, Eberhard-Karls University Tübingen, Germany.
Bihlmayer
A
A
Ammon
H P
HP
Wahl
M A
MA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002463:Cell Membrane Permeability; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D005711:Gallopamil / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic / Q000493:pharmacokinetics / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D011189:Potassium Chloride / Q000494:pharmacology; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology; D014407:Tumor Cells, Cultured
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D007328:Insulin; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D005711:Gallopamil; D011189:Potassium Chloride; D010749:Phosphoprotein Phosphatases; C057862:cyanoginosin LR; D002118:Calcium