Role of different Ca 2+ sources in the superoxide production of human neutrophil granulocytes

Abstract

The role of different Ca 2+ sources in the activation of the NADPH oxidase was investigated in human neutrophil granulocytes. Selective depletion of the stimulus-responsive intracellular Ca 2+-pool and the consequent opening of the store-dependent Ca 2+ channel of the plasma membrane was achieved with thapsigargin, an inhibitor of microsomal Ca 2+-ATPase. Low concentration (10–100 nM) of thapsigargin did not induce any O 2 •−-production, indicating that elevation of [Ca 2+] ic to similar level and probably via similar route as following stimulation of chemotactic receptors, by itself is not sufficient to activate the NADPH oxidase. In significantly higher concentration (1–10 μM) thapsigargin did induce O 2 •−-generation but this effect was not the result of elevation of [Ca 2+] ic. In the absence of external Ca 2+ a gradual decrease of the responsive Ca 2+ pool was accompanied by a gradual decrease of the rate and duration of the respiratory response stimulated by formyl-methionyl-leucyl-phenylalanin. Maximal extent of receptor-initiated O 2 •−-production could only be obtained when the intracellular [Ca 2+] was higher than the resting level. Under this condition Ca 2+ originating from intracellular or external source was equally effective in supporting the biological response.