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.

Divergent effects of co‐carcinogenic phorbol esters and a synthetic diacylglycerol on human neutrophil chemokinesis and granular enzyme secretion

“…Several authors have shown that stimulation of neutrophils by phorbol esters or OAG causes inhibition of agonist-induced and A23187-induced increases in cytosolic Ca2" and speeds the rate of its return towards or below the prestimulation values (e.g. Sha'afi et al, 1983;Fujita et al, 1984;Schell-Frederick, 1984;Rickard & Sheterline, 1985;Naccache et al, 1985;Della Bianca et al, 1986), and we found this too (see Results).…”

“…At least two mechanisms for this effect on calcium are possible: activation of a calcium extruding plasma membrane pump (Lagast et al, 1984;Rickard & Sheterline, 1985), or inhibition of phospholipase Cdependent phosphoinositide turnover in the PMN (Della Bianca et al, 1986), leading to decreased mobilization of cytoplasmic free calcium by inositol trisphosphate. This latter substance is thought to be responsible, at least in part, for calcium mobilization from the endoplasmic reticulum in many cells including neutrophils (Burgess et al, 1984;Prentki et al, 1984).…”

Differentiation‐associated decrease in muscarinic receptor sensitivity in human neuroblastoma cells

“…In PC-12 cells a short term (around 4-10 min) incubation in the presence of TPA leads to a reduction in the rise in cytosolic Ca2+ induced by saturating concentrations of carbachol (Vicentini et al, 1985). Similar short-term effects of TPA on stimulus-induced Ca2 + mobilization have also been observed in other cells where the effects appear, at least in some cases, to be due to an activation of a Ca2+ extrusion mechanism in the cells induced by the phorbol ester through protein kinase C (Rickard and Sheterline, 1985;Tsien et al, 1982b). A more effective Ca2' extrusion mechanism would cause a relative decrease in intracellular Ca2+ stores and thereby limit the rise in cytosolic Ca2+.…”

Analysis of the stimulative effect of thapsigargin, a non‐TPA‐type tumour promoter, on arachidonic acid metabolism in rat peritoneal macrophages

“…However, since TPA has been shown to decrease A23187-or concanavalin Ainduced Ca2+ influx in pig neutrophils (Rickard & Sheterline, 1985), the combined effect by thapsigargin and TPA on arachidonic acid release cannot be explained solely by stimulation of Ca2 + influx. Fourthly, an inhibitor of protein kinases H-7 failed to suppress thapsigargin-stimulated release of radioactivity ( Figure 6).…”