Cytochemical characteristics of astrocytic plasma membranes specialized with numerous orthogonal arrays.

Astrocytic membranes contacting the basal lamina are found to be less affected by filipin than subjacent lateral membranes. An abrupt change in density of lesions induced by filipin creates a border between subpial and lateral membranes at the glia limitans. This means that orthogonal array-crowded membranes may contain relatively less cholesterol than other astrocytic membrane domains. Another possible explanation for filipin resistance is also considered in relation to aggregated intramembrane particles of orthogonal arrays and/or membrane-associated filamentous elements including the basal lamina. The polygonal particle junction between astrocytic processes located just below the subpial membrane is strongly resistant to the action of filipin. Both membrane-associated enzymes, i.e. alkaline phosphatase (AlkPase) and Na+,K+-ATPase are commonly detected only in perivascular astrocytic membranes, and not in subpial membranes, suggesting a regional differentiation in function of astrocytic membranes. There are variations in the reactive deposits particularly of those for Na+,K+-ATPase. It is apparent that the distribution polarity of orthogonal arrays is not connected with that of either AlkPase or Na+,K+-ATPase. Judging from the relative resistance to filipin, however, astrocytes throughout the C.N.S., having domains specialized with orthogonal arrays, may possess a unique stabilizing mechanism for their own membranes contacting the basal lamina.