Immunohistochemical localization of adenylyl cyclase isoforms in the lateral wall of the rat cochlea

The enzymatic activity of adenylyl cyclase (AC) is attributable to nine iso forms with individual pharmacology and tissue distribution. Polyclonal anti bodies for AC isoforms I-IV, VII and VIII were applied to sections of cochl ear lateral wall, a tissue involved in ion transport contributing to the un ique ion content of endolymph and electrical potential of scala media. With in the stria vascularis, immunoreactivity primarily to Ca2+/calmodulin-inde pendent isoforms II, IV and VII was localized to sites consistent in positi on to the basolateral extensions of marginal cells. Little immunoreactivity was observed in the stria vascularis for Ca2+/calmodulin-dependent isoform s I, III and VIII. Within the spiral ligament, type II and type IV fibrocyt es exhibited moderate staining for ACII, IV and VII, less staining for VIII and little for I and III. Immunoreactivity to ACII, IV, Vn and VIII was ob served in type I fibrocytes. The outer sulcus cells and root processes were highly immunoreactive for isoforms I and Vm, but not for III or the Ca2+/c almodulin-independent isoforms. The differential pattern of immunoreactivit y in the lateral wall overall appears to reflect subfamily-specific express ion with Ca2+/calmodulin-independent isoforms expressed in the stria vascul aris and Ca2+/calmodulin-dependent isoforms expressed in the outer sulcus c ells and root processes. cAMP-mediated modulation of ion transport by margi nal cells is predicted to exhibit, in the microenvironment of basolateral m embrane infoldings, pharmacological characteristics of the AC type II subfa mily (II, IV and VII), including activation by protein kinase C (II and VII ). (C) 2000 Elsevier Science B.V. All rights reserved.