Role of a protein regulating guanine nucleotide binding in phosphoinositide breakdown and calcium mobilization by bradykinin in neuroblastoma × glioma hybrid NG108-15 cells: Effects of pertussis toxin and cholera toxin on receptor-mediated signal transduction

Abstract

The addition of bradykinin to NG108-15 cells resulted in an increase in the intracellular Ca 2+ concentration ([Ca 2+] i) and the formation of inositol monophosphate, inositol biphosphate, and inositol trisphosphate in these cells. The bradykinin-stimulated formation of inositol polyphosphates in plasma membrane preparations was dependent on the presence of GTP or guanosine-5′-O-thiotriphosphate (GTPγS) but not of GDP. GTPγS, unlike GTP, increased the basal formation of inositol polyphosphate in NG108-15 membranes. Iontophoretic injection of GTPγS into single cells induced increases in [Ca 2+] i. These effects of bradykinin and GTPγS on [Ca 2+] i and the formation of inositol phosphates in the intact cells and membranes were not affected by treatment of the cells with pertussis toxin or cholera toxin. Data on binding of bradykinin to membrane preparations indicated the presence of two classes of binding sites with K d values of 0.80 ± 0.26 and 9.63 ± 0.13 nM. Approximately 74% of the receptors were in the high affinity state. In the presence of guanyl-5′-yl-imidodiphosphate [Gpp(NH)p], the high affinity sites in the membrane preparations were converted to low affinity sites with no change in the total receptor number. These toxin treatments had no effect on binding of bradykinin to its receptors. Thus. these results indicate that a guanine nucleotide regulatory protein, which is not a substrate of pertussis toxin or cholera toxin, is involved in mediating the effects of bradykinin on membrane-bound phosphoinositide-specific phospholipase C to induce the increase of cytosolic calcium.