DETECTION OF MEMBRANE-BOUND GUANYLATE-CYCLASE ACTIVITY IN RAT C6 GLIOMA-CELLS AT DIFFERENT GROWTH STATES FOLLOWING ACTIVATION BY NATRIURETIC PEPTIDES

We studied the activity and the ultracytochemical localization of memb rane-bound guanylate cyclase (GC) after stimulation with rat atrial na triuretic peptide (rANP), porcine brain natriuretic peptide (pBNP), ra t brain natriuretic peptide (rBNP), or porcine C-type natriuretic pept ide (CNP) in rat C6 glioma cells during proliferation or following exp osure of confluent cells to dibutyryl cyclic AMP. (db-cAMP) or retinoi c acid (RA). Under our experimental conditions all peptides were activ ators of GC as demonstrated by the accumulation of cGMP within cells. During proliferation of C6 cells, the amounts of cGMP remained approxi mately constant. However, at subconfluency, confluency and postconflue ncy, the GC reaction product was located at different sites in C6 cell s. At subconfluency, GC reaction product was on membranes of protoplas mic extensions, at postconfluency, GC reaction product was in associat ion with membranes of cell bodies, and at confluency, both localizatio ns of GC reaction product were detected. Incubation of confluent cells in culture medium containing db-cAMP or RA induced the appearance of long and slender protoplasmic extensions. Under these conditions, the GC reaction product was localized exclusively to these processes. Thes e data suggest that GC is differentially located depending on the stat e of growth of glial cells, and that in differentiating glial cells GC is preferentially located in cell processes.