Summary of TT ultrastructural, electrical, and permeability properties.

+indicates presence/permeable; – absence/; *sum of two TT lengths measured from the cell body to intersection; #if the secondary lamellipodium was outgrowing from the rear lamellipodium, L was indicated as the length of a secondary one; $diameter of the thinnest TT5s could not be measured precisely by conventional optical microscopy; number of experiments is indicated in parenthesis; nd - no data.