Adenylate cyclase and guanylate cyclase activity in the conduction system of rabbit hearts.

In comparison to the working myocytes no remarkable differences in the localization of adenylate cyclase (AC) and guanylate cyclase (GC) were found. The sarcolemmal plasma membrane of the AV node and the Purkinje fibers was the main site of the activity of these two enzymes. GC activity was additionally found at peripheral junctional couplings. Stimulation by hormones and specific activators for both AC and GC was demonstrated with difficulty. The reasons may be more the cytochemical preparation technique than the specificity of the AC and GC in the conducting tissue.