Renal action of cholera toxin: II. Effects on adenylate cyclase-cyclic AMP system

The effects of cholera toxin (CT) on the adenylate cyclase-adenosine 3',5'-cyclic monophosphate (cAMP) system(s) in renal cortex were examined using the isolated renal cortical tubules of rat. Unlike parathyroid hormone, catecholamines or prostaglandins, CT had no immediate effects on cAMP production by the tubules or on adenylate cyclase activity. However, after 30 min of incubation at 37 C, cAMP production by the tubules started to rise and reached a plateau between 60 and 90 min. This rise in cAMP production was not abolished by protein synthesis inhibitors (actinomycin D and cycloheximide) nor by the inhibitors of prostaglandin synthesis (acetyl-salicylate and indomethacin). Repeated washings of the tubules exposed to the toxin for five minutes at 0 or 37 C did not abolish the effect of CT to stimulate cAMP production. Assays of adenylate cyclase activity using homogenates prepared from isolated tubules which were incubated for 60 min with CT revealed an increase in the basal adenylate cyclase activity without any change in NaF-sensitive enzyme activity. It is concluded that CT binds to renal tubule cells rapidly, possibly through energy-independent process. CT stimulates adenylate cyclase activity and increases cAMP production by the renal tubule cells after a latent period of 30 min. The stimulatory effects of CT are not due to new protein synthesis or prostaglandin formation.