Visualization of endocytotic pits in capillary endothelia of dog heart by scanning electron microscopy.

Endocytotic transport may provide a mechanism for myocyte uptake of agents which ameliorate the effects of myocardial ischaemia. Examination of the inner capillary surface by transmission electron microscopy (TEM) is tedious and slow, while use of scanning electron microscopy permits the examination of greater areas in less time. Methods to obtain oblique exposures of capillaries and provide sufficient resolution to observe endocytotic pits were explored. Partial success was achieved using glutaraldehyde fixed tissue, treated with 30% glycerol, frozen-fractured under hexane at -85 degrees C, then dehydrated with acetone at -25 degrees C, critical-point dried and lightly coated with gold. Ultrastructural detail comparable with TEM images of heart tissue was obtained, but the resolution appeared limited by the coating process. It was not possible to verify stimulation of endocytosis by AMP in coronary capillary endothelia with scanning electron microscopy, due to this limitation.