Membrane-associated mucins in normal human conjunctiva.

PURPOSE To examine the presence of specific membrane-associated mucins in normal human conjunctiva. METHODS Glycoconjugates were extracted from membranes with two detergents: octylglucoside and Triton X114. Mucins were separated by cesium chloride density gradient centrifugation. Size was assessed by gel filtration on Sepharose CL2B and charge by ion-exchange chromatography on MonoQ. Cross reaction with antibodies against mucin gene products was assessed in blots of electrophoresis gels. RESULTS Extraction of total tissue membranes yielded material with a buoyant density typical of mucins. Gel filtration showed material reacting with antimucin antibodies in a range of molecular sizes. Agarose electrophoresis confirmed the presence of MUC1 and MUC4 and the absence of MUC2 or MUC5AC. Isolation of membrane mucins by sequential, exhaustive extraction with octylglucoside followed by Triton X114 suggested the existence of mucins in different membrane environments. Reagents to carbohydrate epitopes revealed high mobility material, comigrating with MUC1 and MUC4. Low mobility membrane-bound mucins did not cross-react with any antibodies to mucin genes known to be expressed in human conjunctiva. CONCLUSIONS Membrane-associated mucins are distinct from secreted mucins in normal human conjunctiva. MUC1 and MUC4 mature products decorate the membranes of conjunctival epithelial cells. Their segregation between octyl glucoside and the detergent and aqueous phases of Triton X114 suggests a variety of membrane anchoring modes.