Cyclic GMP-dependent protein kinase-I in the guinea pig cochlea

Recent studies have begun to characterize the nitric oxide/cyclic GMP/protein kinase G pathway in the mammalian cochlea by demonstrating the presence of both the enzyme that produces nitric oxide (NO), nitric oxide synthase, and the NO receptor, soluble guanylate cyclase. The present study investigated protein kinase G (cyclic GMP-dependent protein kinase-I, cGK-I), the downstream enzyme of this pathway that frequently mediates its physiological effects. A commercial antibody to a human cGK-I sequence recognized a protein of appropriate molecular weight in Western blots of guinea pig aorta. Immunostaining of guinea pig aorta was consistent with the expected distribution of cGK-I. In lateral wall tissues of the cochlea, pericytes lining the blood vessels of the spiral ligament were strongly immunoreactive. In the organ of Corti, cGK-I was detected in Hensen's, Deiters', and pillar cells, but not in inner and outer hair cells. This distribution coincides with the localization of soluble guanylate cyclase activity and suggests that cGK-I mediates the effects of the NO/cyclic GMP pathway in the cochlea. It reinforces the hypothesis that the NO/cyclic GMP/cGK-I pathway is involved in regulation of cochlear blood flow and supporting cell physiology.