Na+-H+ exchanger of human placental brush-border membrane

Identification and characterization

D. F. Balkovetz, F. H. Leibach, V. B. Mahesh, Lawrence D Devoe, E. J. Cragoe, V. Ganapathy

Research output: Contribution to journalArticle

57 Citations (Scopus)

Abstract

Syncytiotrophoblast brush-border membrane vesicles isolated from full-term human placentas were shown to transport Na+ against a concentration gradient in the presence of an outward proton gradient ([H+(i)] > [H+](o)). This proton gradient-coupled Na+ uptake was markedly inhibited and the uphill transport abolished when the electrochemical proton gradient was dissipated by carbonylcyanide 4-(trifluoromethoxy) phenylhydrazone. The presence of nigericin also eliminated the concentrative uptake of Na+ in these vesicles. Dimethylamiloride and harmaline inhibited the proton gradient-induced Na+ uptake. The apparent inhibition constant for this process was 0.32 μM for dimethylamiloride and 100 μM for harmaline. The inhibition by dimethylamiloride was freely reversible and the inhibitor reduced the Na+ uptake by directly interacting with the exchange protein rather than by dissipating the H+ gradient. The dimethylamiloride-sensitive Na+ uptake was saturable with respect to Na+. The affinity constant for Na+ was 7.8 ± 1.2 mM and the maximal velocity was 38.7 ± 2.4 nmol · mg protein-1 · min-1. The dimethylamiloride-insensitive Na+ uptake was not saturable and probably represented simple diffusion. The diffusional component accounted for only 10% of the total uptake. Li+ strongly competed with Na+ for the uptake process and the apparent inhibition constant was 3.6 ± 0.4 mM. Tetraethylammonium also caused significant inhibition of Na+ uptake, whereas K+, Rb+, Cs+, and choline had no effect. These data provide evidence for the existence of a Na+-H+ exchanger in human placental brush-border membrane, and the properties of this exchanger are similar to those of the Na+-H+ exchanger identified in the brush-border membrane of mammalian kidney and small intestine. The data also show that virtually all of the carrier-mediated Na+ uptake observed in placental brush-border membrane vesicles under the experimental conditions occurs via the Na+-H+ exchange mechanism.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Cell Physiology
Volume251
Issue number6
StatePublished - Dec 1 1986
Externally publishedYes

Fingerprint

Sodium-Hydrogen Antiporter
Brushes
Microvilli
Protons
Membranes
Harmaline
Nigericin
Tetraethylammonium
Active Biological Transport
Trophoblasts
Choline
Placenta
Small Intestine
Proteins
5-dimethylamiloride
Kidney

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Cell Biology
  • Physiology

Cite this

Na+-H+ exchanger of human placental brush-border membrane : Identification and characterization. / Balkovetz, D. F.; Leibach, F. H.; Mahesh, V. B.; Devoe, Lawrence D; Cragoe, E. J.; Ganapathy, V.

In: American Journal of Physiology - Cell Physiology, Vol. 251, No. 6, 01.12.1986.

Research output: Contribution to journalArticle

Balkovetz, D. F. ; Leibach, F. H. ; Mahesh, V. B. ; Devoe, Lawrence D ; Cragoe, E. J. ; Ganapathy, V. / Na+-H+ exchanger of human placental brush-border membrane : Identification and characterization. In: American Journal of Physiology - Cell Physiology. 1986 ; Vol. 251, No. 6.
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