AJP - Cell Physiology, Vol 255, Issue 5 C641-C652, Copyright © 1988 by American Physiological Society
Role of vesicular transport in ADH-stimulated aggregate delivery
G. Ding, N. Franki, J. Bourguet and R. M. Hays
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
It has been assumed from studies in toad bladder that antidiuretic hormone
(ADH)-stimulated particle delivery to the luminal membrane is mediated by
particle-carrying tubular structures (aggrephores). We report studies in
frog and toad urinary bladder showing that vesicles, rather than
aggrephores, appear to play the major role in particle delivery in the frog
and that vesicle and aggrephore delivery proceed in parallel in the toad.
Our principal evidence for this view is that in the frog, transmission
electron microscopy shows virtually no fused aggrephores. Supporting
evidence includes the following. 1) Freeze-fracture studies show that the
diameters of fusion events delivering particles can be quite small,
indicating that they are formed by fused vesicles rather than fused
aggrephores. 2) A significant population of small fusion events is also
seen in the toad, along with larger fusion events related to both
aggrephores and large vesicles. 3) Surface aggregate areas in both species
are small, consistent with vesicular delivery. 4) Freeze-fracture replicas
indicate delivery from shallow pits. We propose a system of transport of
particles in which aggrephores act largely as intermediate storage
organelles in the frog and as storage and fusion organelles in the toad.
