Expression pattern of adenylyl cyclase isoforms in the inner ear of the rat by RT-PCR and immunochemical localization of calcineurin in the organ of Corti

Most studies concerning adenylyl cyclases in the inner ear were carried out before the advent of molecular biology. In a PCR approach using cDNAs of s ix inner ear tissues (stria vascularis, endolymphatic sac, organ of Corti, vestibulum, cochlear and vestibular nerve) we found tissue specific express ion of adenylyl cyclase isoforms. Adenylyl cyclases types 2 and 4 are predo minant in the fluid controlling tissues, i.e. in the stria vascularis and e ndolymphatic sac. In the organ of Corti and vestibulum the Ca2+-modulated i soforms types 1, 6 and 9 were expressed. The regulation of adenylyl cyclase 9, which is the major isoform expressed in the organ of Corti, proceeds vi a the Ca2+-activated protein phosphatase 2B (calcineurin, PPP3). PCR with s pecific primers for calcineurin demonstrated its abundant expression in the organ of Corti. Using a monoclonal antibody we localized calcineurin immun ochemically to the cochlear nerve, the nerve fibers and the inner hair cell s. In the cochlear and vestibular nerves a characteristic neuronal expressi on pattern of adenylyl cyclase isoforms was observed, i.e. adenylyl cyclase s types 2, 3 and 8. The functional consequences of the adenylyl cyclase exp ression pattern in the inner ear are discussed in conjunction with its uniq ue sensory performance. (C) 1999 Elsevier Science B.V. All rights reserved.