Ion channels in human neutrophils activated by a rise in free cytosolic calcium concentration

A rapid, transient rise in the free cytosolic Ca 2+ concentration ([Ca 2+ ] i ) is one of the earliest events in neutrophil activation and is assumed to be involved in many of the subsequent cellular reactions 1–3 . Both Ca 2+ release from intracellular stores and Ca 2+ influx from the extracellular space contribute to the rise in [Ca 2+ ] i 4 . In an attempt to assess the relative importance of these pools and the sequences leading to the rise in [Ca 2+ ] i , we have studied the time course of changes in [Ca 2+ ] i after stimulation with N -formylmethionyl-leucyl-phenylalanine (fMLP) or platelet-activating factor (PAF) using the Ca 2+ indicators quin-2 and fura-2. We observed a time lag of 1–3 s between stimulation and rise in [Ca 2+ ] i . This lag depends on the agonist concentration but is independent of extracellular Ca 2+ . Thus Ca 2+ release from intracellular stores is rate limiting for the rise in [Ca 2+ ] i . After this, cation channels in the plasma membrane (measured with the patch clamp method 5 ) are opened. These non-selective channels, which also pass Ca 2+ , are activated by the initial rise in [Ca 2+ ] i , but by neither fMLP nor inositol 1,4,5-trisphosphate (IP 3 ) directly.