Role of different Ca2+ sources in the superoxide production of human neutrophil granulocytes

The rule of different Ca2+ sources in the activation of the NADPH oxidase w as investigated in human neutrophil granulocytes. Selective depletion of th e stimulus-responsive intracellular Ca2+-pool and the consequent opening of the store-dependent Ca2+ channel of the plasma membrane was achieved with thapsigargin, an inhibitor of microsomal Ca2+-ATPase. Low concentration (10 -100 nM) of thapsigargin did not induce any O-2(.-)-production, indicating that elevation of [Ca2+](ic) to similar level and probably via similar rout e as following stimulation of chemotactic receptors, by itself is not suffi cient to activate the NADPH oxidase. In significantly higher concentration (1-10 mu M) thapsigargin did induce O-2(.-)-generation but this effect was not the result of elevation of [Ca2+](ic). In the absence of external Ca2a gradual decrease of the responsive Ca2+ pool was accompanied by a gradual decrease of the rate and duration of the respiratory response stimulated b y formyl-methionyl-leucyl-phenylalanin. Maximal extent of receptor-initiate d O-2(.-)-production could only be obtained when the intracellular [Ca2+] w as higher than the resting level. Under this condition Ca2+ originating fro m intracellular or external source was equally effective in supporting the biological response. (C) 1999 Elsevier Science Inc.