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Mol. Hum. Reprod. Advance Access published online on July 22, 2006
Molecular Human Reproduction, doi:10.1093/molehr/gal062
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© The Author 2006. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received May 4, 2006
Revised May 30, 2006
Accepted June 8, 2006

Article

The Na,K-ATPase {alpha}4 isoform from humans has distinct enzymatic properties and is important for sperm motility

Gladis Sanchez 1, Anh-Nguyet T. Nguyen 1, Brady Timmerberg 1, Joseph S. Tash 1, and Gustavo Blanco 1 *

1 Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS, USA

* To whom correspondence should be addressed.
Gustavo Blanco, E-mail: gblanco{at}kumc.edu


  Abstract

In the rat, the Na,K-ATPase {alpha}4 isoform exhibits unique enzymatic characteristics and is important for sperm motility. In this work, we studied expression, localization and function of {alpha}4 in human spermatozoa. We show two catalytically active Na,K-ATPase {alpha} polypeptides with different ouabain affinity and identified expression of {alpha}1, {alpha}4, {beta}1 and {beta}3 isoforms in the gametes. In addition, human sperm presented two Na,K-ATPases composed of {alpha}4, {alpha}4{beta}1 and {alpha}4{beta}3. Kinetic analysis of these isozymes produced in insect cells showed that, compared with human {alpha}1{beta}1, {alpha}4{beta}1 and {alpha}4{beta}3 exhibit higher Na+ and lower K+ affinity and higher sensitivity to ouabain. These particular enzymatic properties suggested a role for {alpha}4 in sperm function. Using computer-assisted sperm analysis (CASA), we found that ouabain inhibition of {alpha}4 significantly decreased percentage sperm motility. In contrast, ouabain did not affect linearity of forward progression, amplitude of lateral head displacement, beat cross frequency and sperm straight-line, curvilinear or average path velocities. This suggests a primary role of {alpha}4 in flagellar motility. Accordingly, we found {alpha}4 in the sperm tail, predominating in the mid-piece of the flagellum. Therefore, similar to the rat ortholog, human Na,K-ATPase {alpha}4 isoform has a distinct activity that is essential for sperm function.

Keywords: {alpha}4 isoform/Na,K-ATPase/ouabain/sperm motility.
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