Molecular structural studies of gap junction protein compositions.

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Gap junction proteins of connexin (Cx) family were examined by using specific rabbit antibodies raised against type-specific peptide sequence domains at the single connexon channel level and on the tissue distiribution and cell type secificity.1. Single gap junction channel (connexon) particles isolated from rat and guinea pig liver by mild detergent extraction showed doughnut-shaped unit particles with central depressions in negative staining and low angle rotary shadowing electron microscopy. Further purification by high performance liquid chromatography followed by affinity chromatogram on either anti Cx26 of anti-Cx32 specific antibody column yielded single western blot pattern without appreciable cosedimentations of other connexins. This result may indicate that single connexon hexamers are composed of either Cx26 of Cx32 only.2. In contrast to the salivary glands which contained both Cx32 and Cx26, lipid secreting Harderian glands showed only Cx26 immunofluorescence in the acinar cells. Myoepithelial cells showed Cx43. In mammary glands, Cx26 and Cx32 in acinar cells and Cx43 in myoepithelial cells revealed dynamic changes of expression during pregnancy, parturition, lactation and weaning period at RNA transcription, protein production, and phosphorylation states, indicating the activity-related expression of gap junction proteins thus consituting functionally distinct cell groups.These results indicate that differential expressions of various gap junction proteins are closely correlated with cell type specific functions and activities.