THAPSIGARGIN INHIBITS CA2+ ENTRY INTO HUMAN NEUTROPHIL GRANULOCYTES

The mechanism of Ca2+ entry after ligand binding to receptors on the surface of non-excitable cells is a current focus of interest. Considerable attention has been given to Ca2+ influx induced by emptying of intracellular pools. Thapsigargin, an inhibitor of microsomal Ca2+-ATPase, is an important tool in inducing store-regulated Ca2+ influx. In the present paper we show that, at concentrations above 500 nM, thapsigargin also has an opposite effect: it inhibits store-regulated Ca2+ influx into Fura 2-loaded human neutrophil granulocytes. As thapsigargin has been frequently applied at concentrations up to 2 mu M, its inhibitory action on plasma-membrane Ca2+ fluxes deserves consideration.