title: Evidence that phorbol ester interferes with stimulated Ca2+ redistribution by activating Ca2+ efflux in neutrophil leucocytes.
abstract: The free calcium ion concentration, [Ca2+]i, in the cytoplasmic matrix of quin2-loaded neutrophil leucocytes increases rapidly after addition of concanavalin A. This increase is effectively abolished by a short (3 min) preincubation with 10 nM-TPA (12-O-tetradecanoylphorbol 13-acetate). TPA also inhibits a [Ca2+]i rise of similar magnitude induced by low concentrations (10 nM) of calcium ionophore A23187, suggesting that phorbol ester does not interfere with a physiological influx mechanism. To investigate the effects of TPA further, cells were depleted of Ca2+ during quin2 loading and then re-equilibrated with normal extracellular [Ca2+]. The return to a stable [Ca2+]i value was preceded by a transient overshoot in [Ca2+]i, implying delayed activation of an efflux mechanism by rising [Ca2+]i. TPA abolished the transient, suggesting preactivation by TPA of the efflux mechanism before Ca2+ influx. TPA also stimulates net Ca2+ efflux from neutrophils and neutrophil cytoplasts. These observations are consistent with the thesis that TPA stimulates a Ca2+-efflux mechanism in these cells.
mesh_terms: D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000097:blood*; D003208:Concanavalin A / Q000494:pharmacology; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D010704:Phorbols / Q000494:pharmacology*; D013552:Swine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D000634:Aminoquinolines; D005456:Fluorescent Dyes; D010704:Phorbols; D003208:Concanavalin A; D013755:Tetradecanoylphorbol Acetate; C035739:Quin2; D002118:Calcium