Ion channels in human neutrophils activated by a rise in free cytosolic calcium concentration.
A rapid, transient rise in the free cytosolic Ca2+ concentration ([Ca2+]i) is one of the earliest events in neutrophil activation and is assumed to be involved in many of the subsequent cellular reactions. Both Ca2+ release from intracellular stores and Ca2+ influx from the extracellular space contribute to the rise in [Ca2+]i. In an attempt to assess the relative importance of these pools and the sequences leading to the rise in [Ca2+]i, we have studied the time course of changes in [Ca2+]i after stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) or platelet-activating factor (PAF) using the Ca2+ indicators quin-2 and fura-2. We observed a time lag of 1-3 s between stimulation and rise in [Ca2+]i. This lag depends on the agonist concentration but is independent of extracellular Ca2+. Thus Ca2+ release from intracellular stores is rate limiting for the rise in [Ca2+]i. After this, cation channels in the plasma membrane (measured with the patch clamp method) are opened. These non-selective channels, which also pass Ca2+, are activated by the initial rise in [Ca2+]i, but by neither fMLP nor inositol 1,4,5-trisphosphate (IP3) directly.
D002118:Calcium / Q000097:blood*; D002122:Calcium Chloride / Q000494:pharmacology; D003600:Cytosol / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology*; D010972:Platelet Activating Factor / Q000494:pharmacology
D007473:Ion Channels; D010972:Platelet Activating Factor; D004533:Egtazic Acid; D009240:N-Formylmethionine Leucyl-Phenylalanine; D002122:Calcium Chloride; D002118:Calcium