Monospecific antiserum against 5'-nucleotidase from Torpedo electric organ: immunocytochemical distribution of the enzyme and its association with Schwann cell membranes

Abstract

The cellular and subcellular distribution of 5'-nucleotidase in tissues of the electric ray Torpedo marmorata has been investigated by means of an antiserum raised against the native enzyme purified from the electric organ. As revealed by immunohistochemistry the enzyme is associated with the surface of the axons of the electric nerves and of spinal nerves. Using the post-embedding colloidal gold technique at the electron-microscopical level 5'-nucleotidase could be located at the plasma membrane of the Schwann cells including the myelin and the fine processes covering the terminal axon ramifications. Also the perineurial sheath of the axons inside the electric organ is 5'-nucleotidase positive. The plasma membrane of the axon and the terminal axon region or the postsynaptic membrane do not contain 5'-nucleotidase. Immunoprecipitation studies using polyacrylamide beads suggest that the ecto-Ca2+- or -Mg2+-adenosine 5'-triphosphatase previously ascribed to synaptosomes of the Torpedo electric organ is not associated with the same membranes as 5'-nucleotidase. Within the electric organ the dorsal plasma membrane of the electroplaque cell, blood capillaries and the connective tissue layer surrounding the columns of electroplaque cells also bind the antibodies. In central nervous tissue solely blood vessels show immunofluorescence. Within the electric lobe both the surface of the electromotor neurons as well as the myelinated axons giving rise to the electric nerve are negative. This also applies to the axons of the optic nerve suggesting that the antiserum is Schwann cell specific, and does not bind to a potential oligodendroglial 5'-nucleotidase. In peripheral tissue the surface of skeletal muscle fibres as well as that of individual myofibrils bind the anti-5'-nucleotidase antibodies. Our results demonstrate that the Schwann cell plasma membrane, including myelin, contains 5'-nucleotidase and that one can distinguish by means of a specific antiserum between Schwann cell and oligodendroglia plasma membranes. The functional significance of the association of 5'-nucleotidase with Schwann cells along the entire surface of axons including the synaptic region as well as with other parts of the electric tissue is discussed regarding its catalytic activity and also the possibility that this surface glycoprotein may be involved in mediating cellular interactions.