AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 2 300-R307, Copyright © 1995 by American Physiological Society
Paracellular solute uptake by the freshwater zebra mussel Dreissena polymorpha
T. H. Dietz, R. A. Byrne, J. W. Lynn and H. Silverman
Department of Zoology and Physiology, Louisiana State University, Baton Rouge 70803, USA.
A hyperosmotic solution of mannitol or glucose (100 mM) in pond water
caused an increase in paracellular solute movement between the bathing
medium and body fluids of Dreissena polymorpha. Small molecules (< 5,000
Da) in the bath entered the mussel, and 80-85% of the sodium and chloride
in the blood was lost within 12 h. Blood total solute was elevated within 4
h of exposure to hyperosmotic conditions, but the rise was attributed to
the gain of glucose or mannitol from the bath and not to an elevation of
ion concentration as a result of the osmotic loss of water. Lanthanum in
the bathing solution was able to penetrate the paracellular junctional
complex between gill epithelial cells in mussels exposed to hyperosmotic
conditions but was rarely observed in pond water-acclimated animals.
Colloidal gold (6 nm diam) was unable to penetrate the paracellular space
but was accumulated in endocytotic vesicles in many epithelial cells. The
"leakiness" of the epithelial tissue may be a critical factor in the low
blood solute concentrations in freshwater mussels despite high rates of ion
transport in these animals.
