GUANINE-NUCLEOTIDES ACTIVATE MULTIPLE SIGNALING PATHWAYS IN PERMEABILIZED GASTRIC CHIEF CELLS - EVIDENCE FOR GTP-GAMMA-S-INDUCED CALCIUM-INDEPENDENT PEPSINOGEN SECRETION

Nonhydrolyzable guanine nucleotide analogues were used to evaluate the role of guanine nucleotide binding (G) proteins in regulating pepsino gen secretion from streptolysin O-permeabilized chief cells from guine a pig stomach. In the presence of 100 nM calcium, 100 muM guanosine 5' -(beta,gamma-imido)triphosphate or guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) caused a 2- to 4-fold increase in pepsinogen secretion. G TPgammaS stimulated secretion in the absence of calcium (up to 10 mM E GTA). With or without added calcium, GTP analogues caused a 2- to 3-fo ld increase in cAMP, whereas guanosine 5'-O-2-(thio)diphosphate and ca lcium alone had no effect on cAMP levels. GTP analogue-induced activat ion of phospholipase C was evidenced by a calcium-independent increase in cytidine diphospho-1,2-diacylglycerol levels (50% above basal). Ph orbol ester- and GTPgammaS-stimulated phosphorylation of a 72-kDa acid ic protein was abolished by an inhibitor of protein kinase C (CGP 4125 1). However, GTPgammaS-induced pepsinogen secretion was only partially inhibited by adding CGP 41251 or a protein kinase C inhibitor peptide . These results indicate that guanine nucleotides activate major signa ling pathways in gastric chief cells. Nevertheless, GTPgammaS can indu ce pepsinogen secretion independently of changes in calcium, cAMP, or activation of protein kinase C.