Structural changes in the apical membrane of lamprey chloride cells after acclimation to seawater

Freeze-fracture replicas demonstrate that the apical membrane of the chloride cells of young adult lampreys (Geotria australis) undergoes a structural change when the animal is acclimated from freshwater to seawater. Although the particles on both the P face and the E face of this membrane are randomly distributed in freshwater animals, they are usually arranged in clusters on both fracture faces in seawater-acclimated animals. Light optical diffraction analysis demonstrates that the particles forming the clusters are periodically arranged. Although comparable clusters of particles have not been recorded in other epithelial membranes that are engaged in transporting ions into a hypertonic environment, they may be involved in the final step of Cl- secretion by the chloride cells of lampreys in seawater.