Ionophore monensin induces Na+-dependent secretion from rabbit neutrophils. requirement for intracellular Ca2+ stores

Rabbit (and human) neutrophils release the secretory enzyme beta-glucuronidase when treated with the ionophore monensin in the presence of Na+. Release of beta-glucuronidase occurs without loss of the cytosol enzyme lactate dehydrogenase and a number of other features of the release process lead us to conclude that a normal exocytotic mechanism is involved. These include sensitivity to metabolic inhibition, enhancement of release induced by cytochalasin B and a requirement for internal sources of Ca2+ when the cells are stimulated with monensin in the absence of extracellular Ca2+. The release process due to monensin differs from that due to receptor directed agonists such as fMet-Leu-Phe and the Ca2+ ionophores A23187 and ionomycin in respect of a prolonged time-course which extends over 20 min; nor do monensin-stimulated neutrophils generate the superoxide anion. The results are discussed in the light of reports which indicate a rôle for Na+ in the activation of neutrophils by other ligands.