Hormonal and purinergic stimulation of bicarbonate secretion in oviducts of rhesus monkey

Abstract

Because an increase in the HCO3− concentration of oviductal liquid at midcycle is believed to markedly enhance fertility, we have studied active secretion of HCO3− across highly differentiated cultures of monkey oviductal epithelium. Cultured cell sheets were mounted in Ussing chambers and bathed in medium containing 25 mM HCO3−. Purinergic agents potently stimulated short-circuit current ( Isc) with an initial transient response declining within ∼2 min to a sustained response. The potency sequence of ATP ≈ UTP > ADP >> AMP suggested that the Isc response was mediated mainly by P2Y2 receptors. Acetazolamide, an inhibitor of carbonic anhydrase, had little or no effect on baseline Isc or the transient response to ATP but abolished the sustained response to ATP. Similar results were obtained on sheets of native epithelium. In pH-stat experiments, the abluminal medium of cell cultures was bathed in HCO3−-CO2 medium, and the pH of the unbuffered luminal medium was maintained at ∼7.4 by addition of strong acid or base. ATP stimulated base secretion, and this was inhibited by acetazolamide. Furthermore, these changes in secretion of base were in good quantitative agreement with the Isc responses. When phenol red (an estrogen) was removed from the culture medium, ATP-dependent HCO3− secretion was markedly reduced but could be restored by treatment with estradiol. Estrogens also markedly increased ciliation of the cultures. These results suggest that the midcycle increase in the HCO3− concentration of oviductal liquid may be mediated by the effects of estradiol on purinergic pathways or on ATP secretion.