THE REGULATION OF STORE-DEPENDENT CA2-60 GRANULOCYTES INVOLVES GTP-SENSITIVE ELEMENTS( INFLUX IN HL)

In granulocytes, emptying of intracellular Ca2+ stores activates Ca2influx across the plasma membrane. To study the putative role of GTP-b inding proteins in this process, we have introduced non-hydrolyzable g uanosine phosphate analogues into the cytosol of non-permeabilized HL- 60 granulocytes using an endocytosis-hypoosmotic shock procedure. At t he cytosolic concentrations obtained (100-500 muM), neither guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) nor guanosine 5'-3-O-(thio)dipho sphate (GDPbetaS) affected basal [Ca2+]i. Call release in response to the receptor agonist fMet-Leu-Phe, the Ca2+-ATPase inhibitor thapsigar gin, or the Ca2+ ionophore ionomycin was also unaffected by GTPgammaS or GDPbetaS. In contrast, the activation of the Ca2+ influx pathway by fMet-Leu-Phe or by thapsigargin was blocked by GTPgammaS but not by G DPbetaS. The GTPgammaS effect was mimicked by NaF. The GTPgammaS and N aF effects were independent of protein kinase C activation and actin p olymerization. Our results demonstrate that a GTP-sensitive element is involved in the signaling between intracellular Ca2+ stores and plasm a membrane Ca2+ channels. The identical effects of GTPgammaS and NaF s uggest that the GTP-sensitive element is a heterotrimeric G-protein.