Arachidonic acid release and catecholamine secretion from digitonin-treated chromaffin cells: effects of micromolar calcium, phorbol ester, and protein alkylating agents.
The relationship between catecholamine secretion and arachidonic acid release from digitonin-treated chromaffin cells was investigated. Digitonin renders permeable the plasma membranes of bovine adrenal chromaffin cells to Ca2+, ATP, and proteins. Digitonin-treated cells undergo exocytosis of catecholamine in response to micromolar Ca2+ in the medium. The addition of micromolar Ca2+ to digitonin-treated chromaffin cells that had been prelabeled with [3H]arachidonic acid caused a marked increase in the release of [3H]arachidonic acid. The time course of [3H]arachidonic acid release paralleled catecholamine secretion. Although [3H]arachidonic acid release and exocytosis were both activated by free Ca2+ in the micromolar range, the activation of [3H]arachidonic acid release occurred at Ca2+ concentrations slightly lower than those required to activate exocytosis. Pretreatment of the chromaffin cells with N-ethylmaleimide (NEM) or p-bromophenacyl bromide (BPB) resulted in dose-dependent inhibition of 10 microM Ca2+-stimulated [3H]arachidonic acid release and exocytosis. The IC50 of NEM for both [3H]arachidonic acid release and exocytosis was 40 microM. The IC50 of BPB for both events was 25 microM. High concentrations (5-20 mM) of Mg2+ caused inhibition of catecholamine secretion without altering [3H]arachidonic acid release. A phorbol ester that activates protein kinase C, 12-O-tetradecanoylphorbol-13-acetate (TPA), caused enhancement of both [3H]arachidonic acid release and exocytosis. The findings demonstrate that [3H]arachidonic acid release is stimulated during catecholamine secretion from digitonin-treated chromaffin cells and they are consistent with a role for phospholipase A2 in exocytosis from chromaffin cells. Furthermore the data suggest that protein kinase C can modulate both arachidonic acid release and exocytosis.
D000098:Acetophenones / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002837:Chromaffin Granules / Q000187:drug effects* / Q000378:metabolism; D002838:Chromaffin System / Q000187:drug effects*; D004072:Digitonin / Q000494:pharmacology*; D005033:Ethylmaleimide / Q000494:pharmacology; D005089:Exocytosis; D050356:Lipid Metabolism; D008274:Magnesium / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D010704:Phorbols / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D000098:Acetophenones; D001095:Arachidonic Acids; D002395:Catecholamines; D010704:Phorbols; D016718:Arachidonic Acid; D008274:Magnesium; D004072:Digitonin; D013755:Tetradecanoylphorbol Acetate; D005033:Ethylmaleimide; C006821:4-bromophenacyl bromide; D002118:Calcium; D009638:Norepinephrine