Palytoxin Acts on Na+,K+-ATPase but not Nongastric H+,K+-ATPase

Palytoxin Acts on Na+,K+-ATPase but not Nongastric H+,K+-ATPase Palytoxin (PTX) opens a pathway for ions to pass through Na,K-ATPase. We investigate here whether PTX also acts on nongastric H,K-ATPases. The following combinations of cRNA were expressed in Xenopus laevis oocytes: Bufo marinus bladder H,K-ATPase α2- and Na,K-ATPase β2-subunits; Bufo Na,K-ATPase α1- and Na,K-ATPase β2-subunits; and Bufo Na,K-ATPase β2-subunit alone. The response to PTX was measured after blocking endogenous Xenopus Na,K-ATPase with 10 μm ouabain. Functional expression was confirmed by measuring 86Rb uptake. PTX (5 nm) produced a large increase of membrane conductance in oocytes expressing Bufo Na,K-ATPase, but no significant increase occurred in oocytes expressing Bufo H,K-ATPase or in those injected with Bufo β2-subunit alone. Expression of the following combinations of cDNA was investigated in HeLa cells: rat colonic H,K-ATPase α1-subunit and Na,K-ATPase β1-subunit; rat Na,K-ATPase α2-subunit and Na,K-ATPase β2-subunit; and rat Na,K-ATPase β1- or Na,K-ATPase β2-subunit alone. Measurement of increases in 86Rb uptake confirmed that both rat Na,K and H,K pumps were functional in HeLa cells expressing rat colonic HKα1/NKβ1 and NKα2/NKβ2. Whole-cell patch-clamp measurements in HeLa cells expressing rat colonic HKα1/NKβ1 exposed to 100 nm PTX showed no significant increase of membrane current, and there was no membrane conductance increase in HeLa cells transfected with rat NKβ1- or rat NKβ2-subunit alone. However, in HeLa cells expressing rat NKα2/NKβ2, outward current was observed after pump activation by 20 mm K+ and a large membrane conductance increase occurred after 100 nm PTX. We conclude that nongastric H,K-ATPases are not sensitive to PTX when expressed in these cells, whereas PTX does act on Na,K-ATPase. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Palytoxin Acts on Na+,K+-ATPase but not Nongastric H+,K+-ATPase

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Publisher
Springer Journals
Copyright
Copyright © 2007 by Springer Science+Business Media, LLC
Subject
Life Sciences; Human Physiology ; Biochemistry, general
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-007-9040-1
Publisher site
See Article on Publisher Site

Abstract

Palytoxin (PTX) opens a pathway for ions to pass through Na,K-ATPase. We investigate here whether PTX also acts on nongastric H,K-ATPases. The following combinations of cRNA were expressed in Xenopus laevis oocytes: Bufo marinus bladder H,K-ATPase α2- and Na,K-ATPase β2-subunits; Bufo Na,K-ATPase α1- and Na,K-ATPase β2-subunits; and Bufo Na,K-ATPase β2-subunit alone. The response to PTX was measured after blocking endogenous Xenopus Na,K-ATPase with 10 μm ouabain. Functional expression was confirmed by measuring 86Rb uptake. PTX (5 nm) produced a large increase of membrane conductance in oocytes expressing Bufo Na,K-ATPase, but no significant increase occurred in oocytes expressing Bufo H,K-ATPase or in those injected with Bufo β2-subunit alone. Expression of the following combinations of cDNA was investigated in HeLa cells: rat colonic H,K-ATPase α1-subunit and Na,K-ATPase β1-subunit; rat Na,K-ATPase α2-subunit and Na,K-ATPase β2-subunit; and rat Na,K-ATPase β1- or Na,K-ATPase β2-subunit alone. Measurement of increases in 86Rb uptake confirmed that both rat Na,K and H,K pumps were functional in HeLa cells expressing rat colonic HKα1/NKβ1 and NKα2/NKβ2. Whole-cell patch-clamp measurements in HeLa cells expressing rat colonic HKα1/NKβ1 exposed to 100 nm PTX showed no significant increase of membrane current, and there was no membrane conductance increase in HeLa cells transfected with rat NKβ1- or rat NKβ2-subunit alone. However, in HeLa cells expressing rat NKα2/NKβ2, outward current was observed after pump activation by 20 mm K+ and a large membrane conductance increase occurred after 100 nm PTX. We conclude that nongastric H,K-ATPases are not sensitive to PTX when expressed in these cells, whereas PTX does act on Na,K-ATPase.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Jul 17, 2007

References

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