Repeating particles associated with an electrolyte-transport membrane

Cells of the pseudobranch gland and chloride cells of the gill filaments of marine Fundulus are characterized by an extensive, interconnected tubular network which is contiguous with the plasma membrane. Treatment with lanthanum salts during fixation results in the deposition within the tubules of an electron-dense substance, which serves as a negative stain for the underlying surface. The outer layer of the plasma membrane is characterized by repeating units 25 Å in diameter similar to those which have been seen on numerous negatively-stained membrane types after isolation. These particles are hypothesized to function in the electrolyte transport activity of the cell types involved.