Intramembraneous particles and transmembraneous ionic channels in the epidermal cell membrane. A cytochemical study...

Normal skin was investigated with the Alcian blue-lanthanum technique. Nexus (gap junctions) were found in the stratum Malpighii. They were less numerous in the basal layer, increasing to the upper layers of the epidermis and lacking in the stratum corneum. They were five-layered, about 20 nm thick and showed a 5-7 nm broad lanthanum positive intercellular dense line. Transitional forms between the narrow intercellular space and the real nexus were observed. These "nearly nexus" were broader, the intercellular dense line measured 6-15 nm, and sometimes they were seven-layered. Both, nexus and "nearly nexus" revealed a specific distribution of lanthanum in their membranes. Lanthanum ions seemed to penetrate the membranes forming electron-dense transversal channels branching off from the central dense line with a periodicity of 3 nm. The tangential sections suggested that this distribution was based on the aggregation of intramembraneous particles 1.5-2.0 nm in diameter, which in some areas may be gathered to greater subunits. The nexus may play a role in the control of epidermal proliferation.