AJP - Cell Physiology, Vol 259, Issue 1 C29-C34, Copyright © 1990 by American Physiological Society
Na(+)-K(4)-Cl- cotransport in cultured cells derived from human retinal pigment epithelium
B. G. Kennedy
Department of Physiology, Northwest Center for Medical Education, Indiana University School of Medicine, Gary 46408.
Unidirectional fluxes of Rb+ and Cl- were measured in cultured human
retinal pigment epithelium (HRPE) to characterize the
Na(+)-K(+)-Cl-cotransport system in this epithelial tissue. In HRPE, the
ouabain-sensitive fraction of Rb+ influx comprises 65% of the total Rb+
influx. Bumetanide [inhibition constant (KI) = 160 nM] inhibited the
residual ouabain-insensitive fraction of Rb+ influx by 70%. The
bumetanide-sensitive fraction of Rb+ influx was dependent on the presence
of both extracellular Na+ and Cl-. Cl- influx was similarly inhibited by
bumetanide and also dependent on extracellular Na+ and Rb+. The
stoichiometry of bumetanide-sensitive Cl- influx to Rb+ influx was 2:1.
Elevation of extracellular osmolarity (by 30%) caused a 2.5-fold increase
in Na(+)-K(+)-Cl- cotransport activity in cultured HRPE. The present study
provides direct evidence for the occurrence of Na(+)-K(+)-Cl-
cotransport-mediated cation and anion transport in HRPE.
