AJP - Cell Physiology, Vol 261, Issue 6 C1025-C1032, Copyright © 1991 by American Physiological Society
Cell-cell channel formation and lectins
E. Levine, R. Werner and G. Dahl
Department of Physiology and Biophysics, University of Miami School of Medicine, Florida 33101.
The oocyte cell-cell channel assay was used to investigate determinants of
the rate of channel formation. After injection of connexin-specific mRNA,
oocytes accumulate a pool of precursors from which cell-cell channels can
form after oocytes are paired. Channel formation was found to be increased
if oocytes are pretreated with lectins before pairing. Several lectins
differing in their carbohydrate binding affinities can exert this effect.
Lectin-specific sugars suppress the effect on cell-cell channel formation
only if the sugar is mixed with the lectin before application to the
oocyte. If the lectin is first bound to the oocyte and then the sugar is
added, no significant inhibition is seen. The promotion of channel
formation by lectins is enhanced by adding an incubation period in regular
medium after lectin treatment, before pairing of the oocytes. Electron
microscopic studies with gold-conjugated lectins show that the lectin
receptors are clustered on the free membrane surface and are taken up in
endocytotic vesicles. These data suggest that the observed acceleration of
cell-cell channel formation by lectins can be attributed to the removal of
steric hindrance, which is a consequence of clustering of the bulky
glycoprotein lectin receptors as well as of the removal from the surface by
endocytosis.
