Expression of the human sodium/proton exchanger NHE-1 in Xenopus laevis oocytes enhances sodium/proton exchange activity and establishes sodium/lithium countertransport

Injection of Xenopus laevis oocytes with rabbit heart poly(A)+RNA results in expression of Na+ inside (Nai+)-dependent Ca2+ uptake activity. The activity was measured by first loading the oocytes with Na+ using nystatin and then incubating the oocytes in K+ or Na+ medium containing 45Ca. The expressed Na+ gradient-dependent Ca2+ uptake was five to eight times that observed with water-injected oocytes or with poly(A)+RNA-injected oocytes for which the Na+ load step had been omitted. Induced activity was related to the amount of RNA injected and was insensitive to nifedipine. Fractionation of the poly(A)+RNA on a sucrose gradient determined that the active message had a size range between 3 and 5 kb. The properties of the Na+ gradient-dependent Ca2+ uptake indicated that Na+-Ca2+ exchange activity had been expressed in X. laevis oocytes. The result may be useful for cloning and identifying the molecular component responsible for Na+-Ca2+ exchange.

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INTRACELLULAR pH AND SODIUM-PROTON EXCHANGE ACTIVITY OF LYMPHOCYTES IN STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

Clinical and Experimental Pharmacology and Physiology ◽

10.1111/j.1440-1681.1991.tb01630.x ◽

1991 ◽

Vol 18 (9) ◽

pp. 589-592 ◽

Cited By ~ 3

Author(s):

Li Di-yuan ◽

Ayame Kobayashi ◽

Yasuo Nara ◽

Katsumi Ikeda ◽

Chuzo Mori ◽

...

Keyword(s):

Intracellular Ph ◽

Spontaneously Hypertensive Rats ◽

Proton Exchange ◽

Hypertensive Rats ◽

Spontaneously Hypertensive ◽

Sodium Proton Exchange ◽

Exchange Activity

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Reduced sodium-proton exchange activity in lymphocytes from transgenic rats.

Hypertension ◽

10.1161/01.hyp.24.3.357 ◽

1994 ◽

Vol 24 (3) ◽

pp. 357-361 ◽

Cited By ~ 4

Author(s):

M Tepel ◽

T Klaus ◽

S Laukemper ◽

W Zidek

Keyword(s):

Proton Exchange ◽

Transgenic Rats ◽

Sodium Proton Exchange ◽

Exchange Activity

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The Sodium/Proton Exchanger Nhx1p Is Required for Endosomal Protein Trafficking in the YeastSaccharomyces cerevisiae

Molecular Biology of the Cell ◽

10.1091/mbc.11.12.4277 ◽

2000 ◽

Vol 11 (12) ◽

pp. 4277-4294 ◽

Cited By ~ 135

Author(s):

Katherine Bowers ◽

Boaz P. Levi ◽

Falguny I. Patel ◽

Tom H. Stevens

Keyword(s):

Protein Trafficking ◽

Protein Sorting ◽

Proton Exchange ◽

Carboxypeptidase Y ◽

Wild Type ◽

Ion Balance ◽

Sodium Proton Exchanger ◽

Sodium Proton Exchange ◽

Prevacuolar Compartment ◽

Vacuolar Protein

We show that the vacuolar protein sorting gene VPS44is identical to NHX1, a gene that encodes a sodium/proton exchanger. The Saccharomyces cerevisiaeprotein Nhx1p shows high homology to mammalian sodium/proton exchangers of the NHE family. Nhx1p is thought to transport sodium ions into the prevacuole compartment in exchange for protons. Pulse-chase experiments show that ∼35% of the newly synthesized soluble vacuolar protein carboxypeptidase Y is missorted in nhx1Δ cells, and is secreted from the cell.nhx1Δ cells accumulate late Golgi, prevacuole, and lysosome markers in an aberrant structure next to the vacuole, and late Golgi proteins are proteolytically cleaved more rapidly than in wild-type cells. Our results show that efficient transport out of the prevacuolar compartment requires Nhx1p, and that nhx1Δ cells exhibit phenotypes characteristic of the “class E” group ofvps mutants. In addition, we show that Nhx1p is required for protein trafficking even in the absence of the vacuolar ATPase. Our analysis of Nhx1p provides the first evidence that a sodium/proton exchange protein is important for correct protein sorting, and that intraorganellar ion balance may be important for endosomal function in yeast.

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