| Abstract: | A method for an analytical isolation of plasma membranes from columnar cells (colonocytes) of the proximal colon of the guinea pig is described. Isolation of the colonocytes was performed by a mild EDTA-chelation method. After homogenization, two subsequent sucrose gradient centrifugations (isokinetic and isopycnic) yielded a plasma-membrane fraction which was enriched 12-fold in (Na+ + K+)-ATPase activity and 8-fold in adenylate cyclase activity. It is suggested that the purified membrane fraction consists mainly of basolateral membranes of the colonocytes. Due to the lack of suitable marker enzymes, no evidence for enrichment of the brush-border membranes was obtained. Histochemical studies demonstrated that alkaline phosphatase is absent from the luminal membrane of the surface epithelial cells of the proximal colon of the guinea pig. |
