Effects of phosphatase inhibitors and a protein phosphatase on norepinephrine secretion by permeabilized bovine chromaffin cells.
A protein phosphatase and phosphatase inhibitors were used to examine the role of protein phosphorylation in the regulation of norepinephrine secretion in digitonin-permeabilized bovine chromaffin cells. Addition of okadaic acid, a potent inhibitor of type 1 and type 2A protein phosphatases, or 1-naphthylphosphate, a more general phosphatase inhibitor, to digitonin-permeabilized chromaffin cells caused about a 100% increase in the amount of norepinephrine secreted in the absence of Ca2+ (in 5 mM EGTA) without affecting the amount of norepinephrine secreted in the presence of 10 microM free Ca2+. This stimulation of norepinephrine secretion by protein phosphatase inhibitors suggests that in the absence of Ca2+ there is a slow rate phosphorylation and that this phosphorylation triggers secretion. Addition of an exogenous type 2A protein phosphatase caused almost a 50% decrease in Ca(2+)-dependent norepinephrine secretion. Thus, the amounts of norepinephrine released both in the absence of Ca2+ and in the presence of Ca2+ appear to depend upon the level of protein phosphorylation.
Wu
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YN
Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Wagner
P D
PD
D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D004988:Ethers, Cyclic / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D019319:Okadaic Acid; D009943:Organophosphorus Compounds / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology
D004988:Ethers, Cyclic; D007093:Imidazoles; D009281:Naphthalenes; D009943:Organophosphorus Compounds; D011506:Proteins; D019319:Okadaic Acid; D014268:Trifluoperazine; C014694:naphthyl phosphate; C031938:calmidazolium; D010749:Phosphoprotein Phosphatases; D002118:Calcium; D009638:Norepinephrine