Ž . Molecular Brain Research 45 1997 325–330 Short communication Expression of adenylyl cyclase type I in cochlear inner hair cells Marian J. Drescher a, ) , Khalid M. Khan b , Kirk W. Beisel c , Ahmad A. Karadaghy a , James S. Hatfield d , Steve Y. Kim a , Andrew J. Drescher a , John M. Lasak a , Roberto L. Barretto a , Ali H. Shakir b , Dennis G. Drescher a,e a Laboratory of Bio-Otology, Department ofOtolaryngology, Wayne State UniÕersity, Detroit, MI, USA b Department of Anatomy, Aga Khan UniÕersity, Karachi, Pakistan c Department of Genetics, Boys Town National Research Hospital, Omaha, NE, USA d Electron Microscopy Laboratory, Veterans Affairs Medical Center, Detroit, MI, USA e Department of Biochemistry, Wayne State UniÕersity, Detroit, MI, USA Accepted 17 December 1996 Abstract Ž . Expression of calciumrcalmodulin-activated adenylyl cyclase type I ACI mRNA has been determined in the cochlea and in an Ž . organ-of-Corti subdissected tissue fraction by reverse transcriptase-polymerase chain reaction RT-PCR analysis. Amplification products of predicted size were obtained from the mouse cochlea and rat organ of Corti with nucleotide sequences corresponding to respective ACI brain transcripts. In addition, ACI template was detected in a rat inner hair cell cDNA library by PCR. Immunoreactivity to ACI has been localized within the organ of Corti to the inner hair cell, with diaminobenzidine staining found in both the cell body and in the stereocilia. Evidence, thus, has been obtained that both ACI transcript and protein are expressed in the inner hair cell, the primary mechanosensory receptor cell of the cochlea. We hypothesize that ACI is activated by calcium influx through a calciumrcalmodulin interaction and that this adenylyl cyclase isoform may have a role in modulation of receptoneural afferent transmission andror mechanosensory transduction in the cochlea. q 1997 Elsevier Science B.V. All rights reserved. Keywords: Adenylyl cyclase type I; RT-PCR; Inner hair cell; Cochlea;Immunohistochemistry Adenylyl cyclases comprise a family of enzyme iso- forms, eachcharacterized by a unique pharmacological pro- Ž . file and tissue distribution. Adenylyl cyclase type I ACI , a Ca 2q rcalmodulin-activated isoform, is selectively ex- pressed with mRNA localized to the brain, retina and w x adrenal medulla 29,30 . Little is known for the organ of Corti of isoform-regu- lated synthesis of cAMP or of cAMP-mediated signal wx w x transduction. Previously, we 5 and others 17 have local- ized adenylyl cyclase enzymatic activity in inner ear sen- sory epithelia at the ultrastructural level of resolution with a cytochemical procedure. Within the sensory epithelium of the trout saccule, reaction product was found to be associated with the outer circumference of stereocilia, in ) Corresponding author. 261 Lande Medical Research Building, Wayne State University School of Medicine, 540 E. Canfield Avenue, Detroit, Ž . MI 48201, USA. Fax: q1 313 577-8137. efferent nerve fibers and in a subpopulation of nerve terminals with both efferent and afferent synaptic special- wx izations 5 . Thus, adenylyl cyclase in the auditoryrvestib- ular end organ may mediate molecular signal transduction at sites associated with mechanosensory transduction and efferentrreceptoneural transmission. Other evidence from studies on the vestibular end organs appears to implicate adenylyl cyclase in modulation of sensory-neural commu- nicationrhair cell function. A cAMP-mediated increase in spontaneous afferent activity in the frog semicircular canal w x has been reported 18 and a baclofen-sensitive ion current Ž . GABA receptor in the mammalian vestibular type I hair B w x cell has been described 13 that potentially is linked to adenylyl cyclase. We report here the application of RT-PCR and immunohistochemistry in identifying the expression of ACI in the organ of Corti and specifically, in the inner hair cell. For the determination of ACI mRNA in the cochlea, 30 Ž CBA mice per preparation Jackson Labs, Bar Harbor, J 0169-328Xr97r$17.00 Copyright q 1997 Elsevier Science B.V. All rights reserved. Ž . PII S0169-328X 97 00007-7