AJP - Cell Physiology, Vol 260, Issue 2 C347-C354, Copyright © 1991 by American Physiological Society
Na(+)-independent Cl(-)-HCO3- exchange in sarcolemmal vesicles from vascular smooth muscle
R. D. Halligan, H. Shelat and A. M. Kahn
Department of Medicine, Medical School, University of Texas Health Science Center, Houston 77225.
Intracellular pH (pHin) affects vascular smooth muscle function, but the
mechanisms that control pHin in this tissue are not well understood. These
studies were performed to determine whether sarcolemmal vesicles from
bovine superior mesenteric artery (SMA) contain a Na(+)-independent
Cl(-)-HCO3- exchanger and, if so, to determine its sensitivity to membrane
voltage and inhibitors. 36Cl- was taken up by vesicles into an osmotically
active intravesicular space. In Na(+)-free media, an outwardly or inwardly
directed HCO3- gradient stimulated 36Cl- transport in the opposite
direction. An outwardly directed unlabeled Cl- gradient stimulated 36Cl-
uptake by a mechanism that was inhibited by external HCO3-. HCO3- or Cl-
gradient-stimulated 36Cl- uptake was not due to voltage coupling between
ions. In the nominal absence of HCO3-, a threefold outwardly directed OH-
gradient did not affect 36Cl- uptake. Total 36Cl- uptake was stimulated by
an inside-positive voltage, but the HCO3- gradient-stimulated component of
36Cl- uptake was insensitive to a change in membrane voltage. Finally,
HCO3- gradient-stimulated 36Cl- uptake was inhibited by
4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and furosemide,
with 50% inhibitory concentration values equalling approximately 1.0 and
0.5 mM, respectively. These data indicate that sarcolemmal vesicles from
bovine SMA contain a Na(+)-independent Cl(-)-HCO3- exchanger. This
transport system is probably electroneutral and is inhibitable by DIDS and
furosemide. A conductive pathway for Cl- is present in the vesicles, but
Cl(-)-OH- exchange activity was not observed.
