Ž . Molecular Brain Research 76 2000 289–298 www.elsevier.comrlocaterbres Research report Immunohistochemical localization of adenylyl cyclase isoforms in the lateral wall of the rat cochlea Marian J. Drescher a, ) , Khalid M. Khan b , James S. Hatfield c , Ali H. Shakir b , Dennis G. Drescher a,d a Laboratory of Bio-otology, Department of Otolaryngology, Wayne State UniÕersity School of Medicine, 261 Lande Medical Research Building, 540 E. Canfield AÕe., Detroit, MI 48201, USA b Department of Anatomy, Aga Khan UniÕersity, Karachi, Pakistan c Electron Microscopy Laboratory, Veterans Affairs Medical Center, Detroit, MI, USA d Department of Biochemistry, Wayne State UniÕersity, Detroit, MI, USA Accepted 21 December 1999 Abstract Ž . The enzymatic activity of adenylyl cyclase AC is attributable to nine isoforms with individual pharmacology and tissue distribution. Polyclonal antibodies for AC isoforms I–IV, VII and VIII were applied to sections of cochlear lateral wall, a tissue involved in ion transport contributing to the unique ion content of endolymph and electrical potential of scala media. Within the stria vascularis, immunoreactivity primarily to Ca 2q rcalmodulin-independent isoforms II, IV and VII was localized to sites consistent in position to the basolateral extensions of marginal cells. Little immunoreactivity was observed in the stria vascularis for Ca 2q rcalmodulin-dependent isoforms I, III and VIII. Within the spiral ligament, type II and type IV fibrocytes exhibited moderate staining for ACII, IV and VII, less staining for VIII and little for I and III. Immunoreactivity to ACII, IV, VII and VIII was observed in type I fibrocytes. The outer sulcus cells and root processes were highly immunoreactive for isoforms I and VIII, but not for III or the Ca 2q rcalmodulin-independent isoforms. The differential pattern of immunoreactivity in the lateral wall overall appears to reflect subfamily-specific expression with Ca 2q rcalmodulin-independent isoforms expressed in the stria vascularis and Ca 2q rcalmodulin-dependent isoforms expressed in the outer sulcus cells and root processes. cAMP-mediated modulation of ion transport by marginal cells is predicted to exhibit, in the Ž . microenvironment of basolateral membrane infoldings, pharmacological characteristics of the AC type II subfamily II, IV and VII , Ž . including activation by protein kinase C II and VII . q 2000 Elsevier Science B.V. All rights reserved. Keywords: Adenylyl cyclase isoform; Cochlea; Stria vascularis; Immunohistochemistry 1. Introduction Ž . Adenylyl cyclase AC , the enzyme of synthesis of the second messenger cAMP, mediates signal transduction in response to external neurotransmitter, hormonal and sen- sory stimuli through coupling to G-proteins. Nine isoforms of AC have been identified, with groupings defined in w x terms of similarity of transcript sequence 25 and similar- ity of function of the corresponding proteins. AC types I, III and VIII are Ca 2q rcalmodulin-activated, II, IV and VII 2q Ž . are Ca -independent members of the type 2 subfamily , 2q Ž and V and VI are inhibited by Ca members of the type . 5 subfamily . Since individual isoforms exhibit specific ) Corresponding author. Fax: q1-313-577-8137; e-mail: mdresch@cmb.biosci.wayne.edu tissue distributions, AC enzymatic activity at a given mem- brane site may reflect one or a mixture of isoforms defin- ing a unique pharmacology in the cAMP-mediated signal w x transduction cascade 19 . In the cochlea, ion transport in the non-sensory epithe- lium of the lateral wall, including the stria vascularis and w q x outer sulcus, is believed to contribute to the high K of endolymph and high positive potential of the endolym- Ž w x. phatic space reviewed by Wangemann et al. 48 . Stria w x AC enzyme activity, localized by Zajic et al. 55 to the basolateral extensions of marginal cells, would be at- tributable to one or more AC isoforms. The known phar- macology associated with each isoform and the preponder- ance of that isoform would predict the pharmacology of cAMP-mediated signal transduction, potentially modulat- ing ion transport, and in particular, K q transport via 0169-328Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-328X 00 00008-5