Characterization of Na+⁄K+-ATPase associated with boar fertility

The ubiquitous transmembrane protein Na⁺⁄K⁺-ATPase affects sperm fertility and capacitation through ion transport and cell signaling, but its effect on in vivo boar fertility, and any controlling mechanism(s) are unknown. The isoforms of the α and β subunits of Na⁺⁄K⁺-ATPase (α1, α2, α3, β1, β2, β3) were assessed in one ejaculate from each of six high and six low fertility boars (HF, LF respectively) which differed in their in vivo direct boar effects (DBE) for both farrowing rate (FR) and litter size (p < 0.05). Sperm function assessed by CASA was similar in HF and LF ejaculated sperm. Immunocytochemistry of the ejaculate sperm found more intact HF than LF sperm had α3 equatorially (p < 0.05), and fewer HF than LF methanol-permeabilized sperm had detectable α2 (p < 0.05). Image Quant analysis of Western blots rigorously quantified the amount of each isoform in the isolated head plasma membrane from each ejaculate, determining that the total amount of the isoform α3, and the amounts of 7 individual α3 bands, differed significantly (HF > LF, p < 0.05), and linear regression confirmed a highly significant relationship of total amount of α3 and α1 with FR (r² = 0.90; p < 0.0001 and r² = 0.36; p < 0.05, respectively). The β1, β2 and β3 isoforms in LF lacked several molecular weight bands common to HF, and the total volume of β1 tended to correlate with DBE for FR (r² = 0.2652; p = 0.09). These findings suggest that specific isoforms of Na⁺/K⁺-ATPase in the sperm head are correlated to boar in vivo fertility, probably through Na⁺⁄K⁺-ATPase's role in capacitation.