AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 5 544-R550, Copyright © 1985 by American Physiological Society
Bicarbonate-chloride exchange in gill plasma membranes of blue crab
S. H. Lee and J. B. Pritchard
The uptake of chloride was studied in gill plasma membrane vesicles from
low-salinity-adapted blue crabs (Callinectes sapidus). Cl- uptake was not
Na+ dependent. However, when a HCO-3 gradient (in greater than out) was
imposed across the membrane, a transient overshoot of about 2.5-fold was
produced. Approximately 90% of the Cl- uptake reflected entry into the
osmotically active intravesicular space. Cl- itself, nitrate, hydroxyl, and
sulfite could substitute for HCO-3. The HCO-3/Cl- exchange process appeared
to saturate at higher concentrations of either HCO-3 or Cl-. The apparent
Km for Cl- was 15 mM. HCO-3-dependent Cl- uptake was significantly
inhibited by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid and
thiocyanate but not by amiloride, furosemide, or ouabain. Alterations in
membrane potential had no effect on Cl- uptake. Addition of Cl- or HCO-3 to
the external medium also accelerated efflux of 36Cl- and H14CO-3 from
preloaded vesicles. These results indicate that the uptake of Cl- by the
crab gill plasma membrane is a carrier-mediated Na+-independent anion
exchange process.
