Localization of Soluble Guanylate Cyclase Activity in the Guinea Pig Cochlea Suggests Involvement in Regulation of Blood Flow and Supporting Cell Physiology

Abstract

SUMMARYAlthough the nitric oxide/cGMP pathway has many important roles in biology, studies of this system in the mammalian cochlea have focused on the first enzyme in the pathway, nitric oxide synthase (NOS). However, characterization of the NO receptor, soluble guanylate cyclase (sGC), is crucial to determine the cells targeted by NO and to develop rational hypotheses of the function of this pathway in auditory processing. In this study we characterized guinea pig cochlear sGC by determining its enzymatic activity and cellular localization. In cytosolic fractions of auditory nerve, lateral wall tissues, and cochlear neuroepithelium, addition of NO donors resulted in three-to 15-fold increases in cGMP formation. NO-stimulated sGC activity was not detected in particulate fractions. We also localized cochlear sGC activity through immunocytochemical detection of NO-stimulated cGMP. sGC activity was detected in Hensen's and Deiters' cells of the organ of Corti, as well as in vascular pericytes surrounding small capillaries in the lateral wall tissues and sensory neuroepithelium. sGC activity was not observed in sensory cells. Using NADPH-diaphorase histochemistry, NOS was localized to pillar cells and nerve fibers underlying hair cells. These results indicate that the NO/cGMP pathway may influence diverse elements of the auditory system, including cochlear blood flow and supporting cell physiology.

Nitric oxide synthase localized in a subpopulation of vestibular efferents with NADPH diaphorase histochemistry and nitric oxide synthase immunohistochemistry

“…Our own observations indicate that both calmodulin and sGC are present at moderate levels in vestibular hair cells and in nerve fibers below the sensory epithelium, as well as at higher levels in cells in the transitional epithelium and dark cell epithelium (Dhaliwal and Lysakowski, 2000). Fessenden and Schacht (1997) however, find no labeling for cGMP, the reaction product of sGC, in hair cells, but instead have found cGMP immunoreactivity in Deiter's and Hensen's supporting cells in the cochlea. Similar results for Hensen's and Claudius cells and for nerve fibers under both inner and outer hair cells have been described by .…”

Heme oxygenase-1 expression in the guinea pig cochlea induced by intense noise stimulation

“…The constitutive neuronal isoform of NOS is present in nerve fibers innervating inner and outer hair cells and spiral ganglion cells [23]. Soluble guanylate cyclase (sGC) and cGK were also localized in supporting structures (Deiters' cells, Hensen's cells, inner and outer pillar cells) of the organ of Corti [24,26]. Previous studies suggested that CO, arising from heme via metabolism by HO, stimulates sGC activity to promote an increase in the cGMP located in neural and cardiovascular tissues [28,29].…”

Distribution of actin and myosin in the cochlear microvascular bed

“…In contrast, sGC. which is activated by NO, was found to be present, together with its second messenger cGMP, in the pericytes of capillaries in the spiral ligament and spiral prominence (21). Fessenden and Schacht (21) considered that the NOS/cGMP pathway in the pericytes may govern cell contractility by lowering levels of Ca*^"^.…”