Early activation of sperm by HCO3- is regulated hormonally in the murine uterus

P>Sperm deposited in the female genital tract receive signals for capacitation. Past work indicates that HCO3- is the initiating signal that the female reproductive tract contains the HCO3--permeant anion channel cystic fibrosis transmembrane conductance regulator (CFTR) and that mutations in CFTR cause subfertility in both sexes. In this study, we examined whether CFTR controls uterine HCO3- content and sperm responses to it. Both CFTR protein and mRNA were absent in prepubertal murine uterus, but appeared in pubertal and adult tissues. Thus, CFTR is upregulated during development. Uterine CFTR mRNA additionally increased upon induced oestrus, most abundantly in uterus body and distal horns. Uterine fluid of oestrous females contained two-, and nearly fourfold more HCO3- than that of dioestrous and prepubertal animals, correlating with increased CFTR expression. For sperm incubated in and recovered from prepubertal uteri, flagellar beat frequency was no different from that before incubation. However, for sperm recovered from dioestrous and oestrous uteri, beat frequency was two- and fourfold higher, respectively. Thus, uterine HCO3- content may have physiological consequences for sperm motility. The male reproductive tract showed no regional distributions or developmental dependence of CFTR expression. Although the sperm flagellum showed CFTR immunoreactivity, CFTR blockers GlyH-101 or CFTRinh-172 did neither diminish HCO3--evoked increases in sperm motility nor protein tyrosine phosphorylation. Our results indicate that in the uterus, both CFTR expression and the supply of HCO3- are upregulated hormonally. We propose that these changes coordinate ovulation with increases in sperm motility and promote other components of capacitation by pathways that do not require CFTR in sperm.