Freeze-fracture electron microscopy: relationship of membrane structural features to transport physiology

Recent observations utilizing freeze-fracturing electron microscopy are discussed which indicate that the membrane structural features visualized by this technique may in some instances be related to specialized membrane transport properties. The occurrence of organized aggregates of intramembrane particles observed in vasopressin or cAMP-treated toad urinary bladder has been found to be closely correlated with induced changes in the permeability of the luminal membrane. Although a cautious interpretation is considered appropriate, these observations raise the possibility that some aspects of hormone action may be restricted to limited regions of membrane. Difficulties in interpretation and some serious limitations of the freeze-fracture technique are discussed.