Isolation and characterization of the urothelial lumenal plasma membrane.

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Abstract
The lumenal plasma membrane was isolated from transitional epithelial cells (urothelium) lining the urinary bladder in sheep by a modified technique involving treatment with hypotonic thioglycolate. The isolated membranes, like those in situ, were distinguished morphologically by arrays of hexagonal particles (in plaque regions) separated by smooth interplaque regions. These plaque regions, specifically, were isolated from the lumenal plasma membrane. Of the proteins constituting the lumenal plasma membrane, 5 characterized the plaque regions and in particular, the 33,000 dalton species appeared most heavily concentrated in the sodium dodecyl sulfate-polyacrylamide gel pattern of the isolated plaque regions. Lipid analyses showed that there were approximately 0.93 mg of phospholipid and 0.27 mg of cholesterol for each milligram of protein, giving a value of 55% lipids and 45% proteins for the composition of the lumenal plasma membrane. The total sialic acid content was approximately 0.038 .mu.mol/mg protein for the plasma membrane. Several plasma membrane marker enzymes were associated with the lumenal plasma membrane fraction, but only the 5''-nucleotidase activity was further enriched in the plaque region fraction. Amino acid analysis of the intrinsic proteins of the plaques indicated a polarity index of 45%.

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