Adenylyl cyclase in the heart: an enzymocytochemical and immunocytochemical approach

This review provides a discussion of the localization of adenylyl cyclase (AC) in normal mammalian heart tissue employing enzymocytochemistry (detection of the catalytic activity of AC by a metal precipitation technique) and immunocytochemistry (immunolabeling of the enzyme protein with antibodies against AC subtypes). By the metal precipitation technique, AC activity was localized in adult guinea pig cardiomyocytes along the sarcolemma and the T-tubule membranes. This reaction can be enhanced by hormones and guanylyl imidodiphosphate, fluoride, and forskolin. With this technique, no precipitates were detected at the sarcoplasmic reticulum. However, under ischemic conditions, AC activity was also found in the junctional sarcoplasmic reticulum of rat cardiomyocytes. Immunocytochemistry revealed AC in the plasma membrane of rat cardiomyocytes. Detection of AC in the perinuclear space of cardiomyocytes might reflect initiation of synthesis and processing of the enzyme protein. Colocalization of AC with cytoskeleton fibers of non-cardiomyocytes emerging in the cell culture of neonatal rat cardiocytes imply a direct cytoskeletal-AC interaction. Finally, it can be stated that the immunolabeling pattern of AC in cryosections of adult and new-born rat hearts reveals a good correspondence with the localization of AC activity in cardiomyocytes demonstrated by enzymocytochemistry.