Cytochemical heterogeneity of the glial plasma membrane: 5?-nucleotidase in retinal M ller cells

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Abstract
Localization of 5′-nucleotidase in the retina of four rodent species was investigated using histochemical and cytochemical techniques. It was revealed by light microscopy that the enzyme is present in the receptor layer, the external nuclear layer and the external plexiform layer. It was found by electron microscopy that the glial cells of the Müller type have a strong activity on their plasmalemma in the enzyme-positive layers. With the exception of weak and scattered activity on some Müller cell processes forming horizontal fibres and the honeycomb meshwork in the ganglion cell layer, none of the internal layers contain 5'-nucleotidase. The asymmetric distribution of this ectoenzyme on the surface of the glial cells is a novel finding and demonstrates a surprising heterogeneity of glial plasmalemma.