Protein phosphorylation at a postreceptor site can block desensitization and induce potentiation of secretion in chromaffin cells.
Desensitization or habituation to repeated or prolonged stimulation is a common property of secretory cells. Phosphorylation of receptors mediates some desensitization processes, but the relationship of phosphorylation to desensitization at postreceptor sites is not well understood. We have tested the effect of protein phosphorylation on desensitization in bovine chromaffin cells. To increase protein phosphorylation, we have used the protein phosphatase inhibitor okadaic acid at 12.5 nM, 100 microM 8-bromo-cyclic AMP to activate protein kinase A, and 10 nM phorbol 12,13-dibutyrate to activate protein kinase C. During repeated 6-s stimulation at 5-min intervals, catecholamine secretion from control cells decreases. Cells exposed to 8-bromo-cyclic AMP or okadaic acid alone show slightly decreased rates of desensitization. In cells pretreated with phorbol 12,13-dibutyrate, desensitization is blocked. Okadaic acid-treated cells stimulated in the presence of 8-bromo-cyclic AMP show potentiation of secretion with repeated stimulation. The protein kinase inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7) increases the desensitization rate. Because these phenomena are observed during secretion evoked with elevated K+ as well as by a nicotinic agonist, the effect of phosphorylation is at a postreceptor site. In contrast to desensitization to the repeated stimulations, desensitization to prolonged stimulation with high K+ is not altered by the above protocols in chromaffin cells.
Program in Molecular and Cellular Biology, University of Massachusetts, Amherst 01003.
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D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D004988:Ethers, Cyclic / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D019319:Okadaic Acid; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism
D004988:Ethers, Cyclic; D007546:Isoquinolines; D010750:Phosphoproteins; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011956:Receptors, Cell Surface; D019319:Okadaic Acid; D015124:8-Bromo Cyclic Adenosine Monophosphate; D015240:Phorbol 12,13-Dibutyrate; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011494:Protein Kinases; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D011188:Potassium