ADENYLYL-CYCLASE IN THE HEART - AN ENZYMOCYTOCHEMICAL AND IMMUNOCYTOCHEMICAL APPROACH

This review provides a discussion of the localization of adenylyl cycl ase (AC) in normal mammalian heart tissue employing enzymocytochemistr y (detection of the catalytic activity of AC by a metal precipitation technique) and immunocytochemistry (immunolabeling of the enzyme prote in with antibodies against AC subtypes). By the metal precipitation te chnique, 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 fors kolin. With this technique, no precipitates were detected at the sarco plasmic reticulum. However, under ischemic conditions, AC activity was also found in the junctional sarcoplasmic reticulum of rat cardiomyoc ytes. Immunocytochemistry revealed AC in the plasma membrane of rat ca rdiomyocytes. Detection of AC in the perinuclear space of cardiomyocyt es might reflect initiation of synthesis and processing of the enzyme protein. Colocalization of AC with cytoskeleton fibers of non-cardiomy ocytes emerging in the cell culture of neonatal rat cardiocytes imply a direct cytoskeletal-AC interaction. Finally, it can be stated that t he immunolabeling pattern of AC in cryosections of adult and new-born rat hearts reveals a good correspondence with the localization of AC a ctivity in cardiomyocytes demonstrated by enzymocytochemistry. (C) 199 8 Wiley-Liss, Inc.