title: The α4 isoform of the Na⁺,K⁺-ATPase is tuned for changing extracellular environments.
abstract: In their journey from the male to the female reproductive tract, spermatozoa are confronted with a constantly changing environment. To cope with the associated challenges, spermatozoa express a distinct set of transporters, channels and pumps. One of the membrane proteins unique to spermatozoa is the α4 isoform of the Na(+) ,K(+) -ATPase. In addition to α4, spermatozoa express the ubiquous α1 variant. To get a detailed understanding of how α1 and α4 differ, and why spermatozoa need an additional Na(+) ,K(+) -ATPase, we have conducted an electrophysiological comparison of the rodent isoforms (rat α4 versus mouse α1-3) using the Xenopus oocyte expression system. We demonstrate isoform-specific differences in the voltage sensitivity of steady-state turnover, with α2 being the more sensitive, and α1 and α2 having faster Na(+) release kinetics than α3 and α4. Our data further show that the α1 and α2 turnover rates are fast compared with those of α3 and α4. Finally, α4 is less influenced by changes in extracellular Na(+) and temperature than α1. Based on these findings, we discuss the possibility that evolution has selected robust activity rather than rapid turnover for α4.
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, Denmark.
authors.forename: Michael Voldsgaard
authors.initials: MV
authors.lastname: Clausen
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, Denmark.
authors.forename: Poul
authors.initials: P
authors.lastname: Nissen
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, Denmark.
authors.forename: Hanne
authors.initials: H
authors.lastname: Poulsen
mesh_terms: D000818:Animals; D008297:Male; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000502:physiology; D013696:Temperature; D014982:Xenopus laevis
chemical_list: C526097:Atp1a3 protein, mouse; C485720:Atp1a4 protein, rat; C497344:Atp1a1 protein, mouse; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium
keywords: Na+,K+-ATPase; adaptation; isoforms; sperm; voltage dependence