Pharmacology of receptor operated calcium entry in human neutrophils.

In neutrophils, increases in intracellular calcium [Ca(2+)](i) provide a crucial link between inflammatory mediators and inflammatory responses. The modulation of [Ca(2+)](i) fluxes in non-excitable cells such as neutrophils has been studied for more than 25 years yet remains to be resolved. In these cells, the Ca(2+) influx can occur through at least two mechanisms, as follows: one dependent on the state of filling of the endoplasmic reticulum Ca(2+) stores, termed store operated calcium entry (SOCE), and the other less studied mechanism in neutrophils which is not dependent on the state of the Ca(2+) stores but is regulated by receptor occupation, termed receptor operated calcium entry (ROCE).

Discrimination between receptor- and store-operated Ca(2+) influx in human neutrophils.

Ca(2+) and Sr(2+) entry pathways activated by pro-inflammatory agonists FMLP, LTB(4) and PAF have been compared to thapsigargin in human neutrophils. 2-APB (10microM) increased Ca(2+) influx and to a greater extent in agonist than in thapsigargin stimulated neutrophils. This action of 2-APB was specific to Ca(2+) because 2-APB did not augment Sr(2+) entry in agonist and thapsigargin stimulated neutrophils.

Actions of calcium influx blockers in human neutrophils support a role for receptor-operated calcium entry.

The action of two potent store operated Ca2+ entry (SOCE) inhibitors, ML-9 and GdCl3 on Ca2+ fluxes induced by the pro-inflammatory agonists FMLP, PAF, LTB(4) as well as the receptor-independent stimulus thapsigargin has not been documented in human neutrophils. In this study, ML-9 enhanced both release and subsequent Ca2+ influx in response to agonists whereas it enhanced Ca2+ release by thapsigargin, but inhibited Ca2+ influx. In contrast, 1muM GdCl3 completely inhibited Ca2+ influx in response to thapsigargin, but only partially blocked Ca2+ influx after agonist stimulation.

Relationship between calcium release and NADPH oxidase inhibition in human neutrophils.

The aim of this study was to investigate the possible relationship between NADPH oxidase activity and changes in cytosolic Ca(2+) in response to different agonists. Treatment of neutrophils with leukotriene B4 (LTB(4)) demonstrated characteristic changes to cytoslic Ca(2+) yielding an EC(50) of 4nM. The pA(2) values for the specific LTB(4) receptor (BLT) antagonists, U-75302 and LY-255283 were 6.

Swell activated chloride channel function in human neutrophils.

Non-excitable cells such as neutrophil granulocytes are the archetypal inflammatory immune cell involved in critical functions of the innate immune system. The electron current generated (I(e)) by the neutrophil NADPH oxidase is electrogenic and rapidly depolarises the membrane potential. For continuous function of the NADPH oxidase, I(e) has to be balanced to preserve electroneutrality, if not; sufficient depolarisation would prevent electrons from leaving the cell and neutrophil function would be abrogated.