Quick-freeze deep-etch image of two decorated tubules with helically wound subunits on their cytosolic surfaces. Each step in a helical turn appears to be formed of three dyads lying side by side across the row. Each dyad appears to be independent with the other two dyads at each step. Thus each helical row apparently consists of a long series of three dyads lying end to end rather than two rows of subunits. This accounts for the three lines per helix observed in some studies (McKanna, J. Ultrastruct. Res. 54:1-10, 1976. Following the tubules downward in this picture the fracture exposes the inside of one tubule and IMPs exposed here may represent the luminal transmembrane extensions of their much larger heads that appear on the cytosolic surface of the tubule. Additionally, a filled collecting canal lies near the decorated tubules with its P-fracture face exposed that is studded with IMPs. A row of indentations leading to openings to the smooth spongiome and holes in a second row are visible. IMPs appear to have different diameters on this P-face and some are organized into rows. The content of the collecting canal lumen has a uniquely etched pattern distinguishing it from other vacuoles and the cytosol. Adapted with permission from the Journal of Cell Science. TEM taken on 6/22/88 by C. Schroeder with Zeiss 10A operating at 60kV. Neg. 31,500X. The raw film was scanned with an Epson Perfection V750 Pro. This image is best used for quantitative analysis. Additional information available at (http://www5.pbrc.hawaii.edu/allen/).