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Journal of Experimental Biology, Vol 159, Issue 1 359-369, Copyright © 1991 by Company of Biologists

JOURNAL ARTICLES

Characterization of an endogenous Na+/H+ antiporter in Xenopus laevis oocytes

DW Towle, A Baksinski, NE Richard and M Kordylewski
Department of Biology, Lake Forest College, IL 60045.

The amiloride-sensitive Na+/H+ antiporter in defolliculated oocytes of Xenopus laevis was characterized by measurements of 22Na+ influx and apparent H+ efflux. Uptake of 22Na+ was linear over a 90-min incubation period and was inhibited approximately 80% with 5 x 10(-4) mol l-1 amiloride. Amiloride-sensitive sodium uptake was reduced following collagenase treatment or oocyte aging. K0.5 for amiloride inhibition was 4.13 x 10(-6) +/- 1.33 x 10(-6)mol l-1 and the Km for Na+ was 4.25 x 10(-3) mol l-1. Hill analysis of the kinetic data for Na+ revealed an nH value of 1.14, indicating an absence of interacting binding sites for Na+. Parallel measurements of amiloride-sensitive Na+ uptake and H+ efflux indicated a Na+/H+ exchange ratio of 0.88:1. Our conclusion is that the Na+/H+ antiporter of Xenopus oocytes exhibits a nominal 1:1 Na+/H+ exchange stoichiometry and is similar in its properties to the antiporter of other vertebrate cells.


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© The Company of Biologists Ltd 1991