AJP - Cell Physiology, Vol 259, Issue 3 C413-C420, Copyright © 1990 by American Physiological Society
Chloride transport across the membrane of parotid secretory granules
K. W. Gasser and U. Hopfer
Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
The Cl- transport pathways in secretory granules isolated from the parotid
glands of rats were characterized by the technique of ionophore-induced
lysis in defined salt solutions. The granules were shown to possess a Cl-
conductance that exhibited a distinct anion selectivity with a sequence I-
greater than Br- greater than Cl- greater than F- greater than SO4(2-) much
greater than gluconate-. This conductance could be reduced approximately
40% by the stilbene 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic
acid (SITS) from the cytoplasmic side; the half-maximal concentration for
inhibition was 50 microM. Furthermore, the apparent Cl- conductance was
reduced by outwardly directed granule H+ gradients and stimulated by
inwardly directed gradients. An outwardly directed H+ gradient mimics the
in vivo environment and may serve in a regulatory capacity, providing for a
tonic inhibition of transport until the granule fuses with the luminal
membrane. The granules also possessed a Cl(-)-HCO3- exchange based on
electroneutrality of Cl- uptake and stimulation of this uptake by HCO3-.
This pathway displayed a different anion selectivity, I- greater than Br-
greater than F- greater than Cl- much greater than SO4(2-) much greater
than gluconate-, and was not inhibited by SITS on the cytoplasmic side. The
presence of these electrolyte transport pathways in the granule membrane is
consistent with the production of primary fluid by parotid acinar cells
after fusion of granules with the luminal plasma membrane.
