Protein phosphatase inhibitors exert specific and nonspecific effects on calcium influx in thapsigargin-treated human neutrophils.
C2-ceramide but not inhibitors of phosphatase types 1 and 2A (okadaic acid, calyculin A, tautomycin) blocked store-regulated Ca2+ entry induced in human neutrophils by thapsigargin. This contrasts with previous results showing that both types of compounds inhibit Ca2+ influx in fmet-leu-phe-treated cells. In present studies, phosphatase inhibitors increased the rate of secondary Ca2+ influx in a temperature-dependent manner. Their mechanism of action appeared to be independent of phosphatase inhibition since the inactive congeners, norokadaone and tetraacetyl okadaic acid, also potentiated Ca2+ influx at similar concentrations. When Ca2+ stores were predischarged by thapsigargin, okadaic acid but not norokadaone acted synergistically with fMLP to inhibit subsequent Ca2+ entry. Results suggest that blockade of Ca2+ influx in neutrophils is mediated by a phosphorylation reaction that is prolonged by phosphatase inhibitors. The requisite phosphorylation occurs in fMLP-activated cells but may be absent in cells incubated with thapsigargin.
Wong
K
K
Department of Pharmacology and Therapeutics, University of Calgary, Alberta, Canada.
Li
X B
XB
D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D019284:Thapsigargin / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D019284:Thapsigargin; D010749:Phosphoprotein Phosphatases; D002118:Calcium