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Mol. Hum. Reprod. Advance Access originally published online on July 22, 2006
Molecular Human Reproduction 2006 12(9):565-576; 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

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

Gladis Sanchez, Anh-Nguyet T. Nguyen, Brady Timmerberg, Joseph S. Tash and Gustavo Blanco1

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

1 To whom correspondence should be addressed at: Department of Molecular and Integrative Physiology, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA. E-mail: gblanco{at}kumc.edu

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, ß1 and ß3 isoforms in the gametes. In addition, human sperm presented two Na,K-ATPases composed of {alpha}4, {alpha}4ß1 and {alpha}4ß3. Kinetic analysis of these isozymes produced in insect cells showed that, compared with human {alpha}1ß1, {alpha}4ß1 and {alpha}4ß3 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.

Key words: {alpha}4 isoform/Na,K-ATPase/ouabain/sperm motility


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