EXPRESSION AND CELLULAR-LOCALIZATION OF THE KALLIKREIN-KININ SYSTEM IN HUMAN OCULAR-TISSUES

Tissue kallikrein is a serine proteinase which processes kininogens to release bioactive kinins. Kinins mediate a variety of biological proc esses through the interaction with kinin receptors. Kinins are involve d in the regulation of blood pressure and local blood flow, vasodilati on, smooth muscle contraction and relaxation, production of pain and i nflammation, and stimulation of cell proliferation. The tissue kallikr ein-kinin system has been implicated in a number of pathophysiological processes such as hypertension, allergy and diabetes mellitus. In the present study, we have identified the expression and localization of components of the kallikrein-kinin system in the human eye by reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot ana lyses, and in situ hybridization histochemistry. RT-PCR and Southern b lot analyses have detected mRNAs of the key components of the system i ncluding tissue kallikrein, low molecular weight kininogen, and bradyk inin B-1 and B-2 receptors at high levels in human retina, choroid and ciliary body, and relatively low levels in the optic nerve. In situ h ybridization has identified cellular localization of these four mRNAs in ocular tissues. They are expressed in retinal neuronal cells includ ing the outer nuclear layer, inner nuclear layer and ganglion cell lay er. These mRNAs were also identified in endothelial cells of ocular bl ood vessels, ciliary muscle and lens epithelial cells. The sense ribop robes showed negative staining, which indicates the specificity of the antisense riboprobes. These results suggest that the tissue kallikrei n-kinin system is produced endogenously in human ocular tissues. Simil ar expression patterns of kallikrein, kininogen and kinin receptors in dicate that the kallikrein-kinin system may function in an autocrine o r paracrine fashion in the eye. (C) 1996 Academic Press Limited