The effects of temperature on ferritin transport by endothelial cell vesicles in the capillaries of the frog mesentery.

Using electron microscopy we have determined the appearance of ferritin in the endothelial cell vesicles of frog mesenteric capillaries after varying periods of exposure of the luminal surface of the cell to a ferritin solution, at 17-20 degrees C and at 4-7 degrees C. At 17-20 degrees C, the pattern of labelling observed in the absence of flow through the capillary is very similar to that previously described by us in continuously perfused capillaries [1]. Some vesicles are labelled after the shortest exposures (less than 1 sec) and labelling increases with exposure to reach steady values at 40-60 s. At 4-6 degrees C, a similar initial level of labelling is observed. There is, however, no further increase in labelling as the period of exposure is increased. The effect of temperature on the uptake and transfer of ferritin by the endothelial cell vesicles is consistent with our previous view. We suggest that the cavities of the rapidly labelling vesicles communicate directly with the capillary lumen [1], and their labelling should be unaffected at low temperatures. The secondary, slow rise in labelling, we suggested, resulted from fusions of adjacent vesicles and we would expect this process to be abolished at low temperature.