TRIDIMENSIONAL ULTRASTRUCTURE OF FENESTRATED CAPILLARIES

Fenestrated capillaries in the renal papilla of the mouse were studied with freeze-etch electron microscopy. Both cross sections and en face views of the luminal and basal plasma membranes, the their cytoplasmic and external aspects, were obtained. The fenestrations measured 650 Å units across and numbered up to 60 per square micron. It is calculated that fenestrations may constitute 20% of the surface area where they lie closely together, and approximately 15% of the whole cell. The fenestrations sometimes seemed to be closed by a septum with a central knob, but more often there seemed to be no such septum. It could be confirmed that models of these cells proposed by earlier investigators on the basis of conventional methods, were essentially correct. © 1968 Academic Press Inc.