Immunohistochemical evidence of the extracellular localization of calcium-activated neutral protease (CANP) in rabbit skeletal muscle, lung and aorta.

The subcellular localization of calcium-activated neutral protease requiring a millimolar calcium concentration (m-CANP) was examined by light and electron microscopy in various tissues of the rabbit, using an immunoperoxidase method with a monoclonal antibody (1C6D1). In skeletal muscles, specific staining for m-CANP was recognized on collagen fibrils (ca 40 nm in diameter) with a periodic banding pattern. In the lung, dense reaction products were precipitated on elastic fibers under the bronchial epithelia. In the aorta, tunica intima and adventitia were intensely stained. Dense reaction products were observed on collagen fibrils and elastic fibers. Basal laminae, on the other hand, were not stained by anti m-CANP antibody in these tissues. These findings suggest that m-CANP may be involved in the regulation of the structure and function of the extracellular matrix.