DEVELOPMENTAL-CHANGES IN ANP-STIMULATED GUANYLYL CYCLASE ACTIVITY ENHANCED BY ATP IN RAT LUNG MEMBRANE-FRACTIONS

1 ANP (atrial natriuretic peptides)- or ANP/ATP-stimulated guanylyl cy clase activities were compared in adult (2 month old) and neonatal (5- 7 day old) rat lung membrane fractions. 2 The enzyme activities of bot h membranes depended on the incubation time and ATP concentration: alt hough the activities of both membranes were similar after a short incu bation time (4 min), those in adult membranes were lower than those of neonatal membranes after longer incubation times (10 and 30 min) or a t lower concentrations of ATP. 3 ANP/ATP gamma S-stimulated guanylyl c yclase activities, which were much higher than ANP/ATP-stimulated acti vities, were similar in both membranes. 4 ATPase activity of adult mem branes was higher than that of neonatal membranes, suggesting that hyd rolysis of ATP leads to a decrease of ANP/ATP-guanylyl cyclase activit y in adult membranes. Triton X-100 enhanced and diminished ANP/ATP-sti mulated guanylyl cyclase activities of adult and neonatal membranes, r espectively, and thereby abolished the adult/neonatal difference in th e membrane response to ATP. 5 ANP-stimulated activities of both membra nes were much more activated by pre-incubation with ATP gamma S than t hose induced by simultaneous addition of ATP gamma S. The former activ ities were decreased to levels of the latter by Triton X-100. The latt er activities were not affected by Triton X-100. 6 The present results suggested that conformation of lung plasma membranes is related to ac tivation of the ANP receptor/guanylyl cyclase system.