Adenosine and guanosine 3',5' cyclic monophosphate phosphodiesterase activities in rat small and large bowel following single and multiple exposure to 1,2-dimethylhydrazine

The hydrolytic activities of adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) phosphodiesterases (PDE) in rat large and small bowel tissue were determined after exposure to the colon carcinogen 1,2-dimethylhydrazine (DMH). Immediate increases in the cAMP-PDE activities were found in the tissues after a single exposure to the chemical which returned towards normal while chronic exposure resulted in no visible changes. The increased cAMP-PDE activities may be the factor responsible for the diminished intracellular cAMP concentrations found after exposure to the carcinogen. In contrast, the cGMP-PDE activities changed little in the colon and increased in the small bowel, suggesting that the determinant for the increases in the concentration cGMP was the activation of guanylate cyclase enzymes following exposure to DMH. Ratios of cAMP to cGMP and cAMP-PDE to cGMP-PDE in the colon showed major changes after carcinogenic insult by the DMH, suggesting that such measurements might serve as useful markers for exposure to environmental toxicants.

Distribution and localization of adenosine 3':5'-monophosphate-dependent protein kinase in mammalian artery

Among the three major vascular layers (the intima-inner, the media-middle smooth muscle, and the adventitia-outer connective tissue) over 90% of the total protein kinase activity was observed in the middle layer. Of various subcellular fractions of the vascular smooth muscle, the 105,000 g supernatant (cytosol fraction) showed the highest specific activity and represented more than two thirds of the total kinase present in this layer. DEAE-cellulose chromatography of the soluble enyzme revealed the existence of two major forms of cyclic AMP-dependent protein kinase, type I and type II, of which 60% of the total enzymatic activity was found in type II. A divalent cation was found to be essential for their phosphotransferase activity. Only Mg2+ and Co2+, but not Zn2+, Mn2+ or Ca2+ could satisfy the cation requirement. The phosphorylated substrate had the characteristics of a protein with a phosphoester bond.

Role of cyclic AMP in rat aortic microsomal phosphorylation and calcium uptake

The role of adenosine 3',5'-monophosphate (cyclic AMP)-dependent membrane phosphorylation in the regulation of microsomal calcium transport in rat aortic smooth muscle was studied. Cyclic AMP-dependent protein kinase augmented the phosphorylation of serine residues in a microsomal protein component with a molecular weight of about 44,000 (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and the majority of 32P incorporation was in serine residue(s). The phosphorylated protein had stability characteristics of a phosphoester. The phosphorylated substrate was not extracted from the trichloroacetic acid (TCA) precipitate with organic solvents or by suspension in hot TCA; and the demonstrated hydroxylamine insensitivity suggested that the substrate was not lipid or nucleic acid. Intrinsic phosphoprotein phosphatase cleaved the labeled phosphate from the cyclic AMP-stimulated microsomes in the first 5 min of incubation. Microsomes phosphorylated in the presence of 1 micron cyclic AMP or 1 micron cyclic AMP plus 0.1 mg/ml protein kinase exhibited enhanced calcium uptake. We suggest that reversible phosphorylation of microsomal membranes may play an important role in the regulation of aortic microsomal calcium transport by cyclic AMP.