Metabolism of adenosine 3′,5′-monophosphate by epithelial cells of the toad bladder

Abstract

When whole urinary bladders of the toad were incubated with adenosine 3′,5′-monophosphate-³H (cyclic AMP-³H) > 95% of the radioactivity could be extracted from the tissue with trichloroacetic acid (TCA). The TCA-soluble radioactivity was separable by cation-exchange (Dowex-50) chromatography into residual cyclic AMP-³H, 5′-AMP-³H, adenosine diphosphate (ADP)-³H and inosine-³H. Thus, neither substantial tight binding of cyclic AMP to TCA-precipitable cell constituents nor any novel metabolite of cyclic AMP were found. On exposure of cyclic AMP-³H to a crude homogenate of the epithelial cells scraped from the mucosal face of the bladder, the principal metabolite was inosine-³H, whereas 5′-AMP-³H was either absent or present in undetectible amounts. However, when the homogenate included added 5′-AMP (2 × 10^-2 mole/liter), substantial quantities of 5′-AMP-³H were recovered. Metabolism of cyclic AMP-³H by homogenates of the epithelial cell scrapings from the bladder was strongly stimulated by alkalinization over the range in pH of 6-9. Theophylline inhibited metabolism of cyclic AMP only to a limit of 50%, the inhibition being limited to the OH^--stimulated component. These results suggest the possibility that a second pathway for metabolism of cyclic AMP may exist. If such is the case, its relationship, if any, to the ultimate biological effects of cyclic AMP within cells will be studied.