Calcium Channel Blockers Nifedipine and Diltiazem Inhibit

We have undertaken a detailed study of the mechanisms of maintenance of intracellular Ca2+ homeostasis in human polymorphonuclear neutrophils (PMN) and its implications for phagocytosis and IgG Fc receptor (FcR) signaling. When PMN were incubated in Ca2+free medium, cytoplasmic calcium concentration ([Ca"+Ii) was markedly depressed and intracellular stores were depleted of calcium. [Ca2+Ii n these depleted cells increased within l min when PMN were placed in medium containing Ca2+ and then decreased to a level close to the normal basal [CaZ+li, replenishing the intracellular Ca2+ pools. Lac13 prevented entry of Ca2+ into Ca2+-depleted PMN, but the calcium channel blockers nifedipine, diltiazem, and verapamil did not. Nifedipine and diltiazem but not verapamil inhibited the movement of Ca2+ from cytosol to intracellular stores. Nifedipine and diltiazem inhibited the normal increase in [Ca2+Ji from aggregated IgG binding to FcR and also prevented formyl-methionyl-leucyl-phenylalanine (fMLP)-induced [Ca2+Ii rise. Verapamil had no effect on either an fMLPor IgG-mediated increase in [Ca2+Ii. Consistent with this, nifedipine and diltiazem inhibited fMLP-stimulated phagocytosis (which is dependent on an increase in [Ca2+]i) when PMN had repleted intracellular stores. In contrast, Lac13 inhibited fMLP-stimulated ingestion only in PMN which had intracellular stores depleted. None of these compounds had any effect on phorbol dibutyrate-stimulated ingestion (which is independent of a [Ca2+Ii rise). In summary, these data show that Ca" is in rapid equilibrium between intracellular and extracellular compartments in PMN. Exchange of cytoplasmic Ca2+ with the extracellular space is inhibited by LaCl3, while exchange of Ca" between the cytosol and intracellular stores is inhibited by the dihydropyridine nifedipine and the benzothiazepine diltiazem. These data suggest that these drugs, which are known to regulate some plasma membrane Ca2+ channels in excitable cells, can also regulate Ca2+ release from intracellular stores in PMN and that this regulation may have significant effects on PMN function.