Our laboratory has been studying proton secretory pathways in the kidney for a number of years, and we are now applying this knowledge and experience to the male reproductive tract. The epididymis is the site where spermatozoa are matured and stored, but very little is known about the regulation of epididymal epithelium functions. The lumen of the epididymis is maintained at an acidic pH, which is involved in sperm maturation and in the maintenance of sperm in a quiescent state during their storage in and passage through this system of tubules. However, despite this important function in male reproduction function, the cellular and physiological regulation of proton secretion along the male reproductive tract has not been well characterized.

We have recently shown, in rat, that a bafilomycin-sensitive, proton-pumping H+ATPase is concentrated in apical membranes of specialized epithelial cells in the epididymis and vas deferens. This proton pump is a major contributor to luminal acidification since it is responsible for up to 80% of proton secretion. Proton secretion is a complex process that requires additional transport proteins to work in conjunction with the proton pump. We are now currently characterizing this acidification mechanism by determining the nature of these transport proteins and by examining the regulation of proton secretion in the male reproductive tract.

The ultimate aim of this research is to understand how defective acidification may impair reproductive function in pathologic states, and how intervention to manipulate acidification may eventually be used to control male fertility. It is clear that if the luminal pH can be artificially increased by inhibiting the proton pump, sperm would become prematurely motile and would exhaust their limited energy supplies before ejaculation occurred. Thus, this can be widely seen as a means of intervention to control male fertility - i.e. we have identified a potential target molecule for a male contraceptive. In addition, however, a failure in some men to acidify normally might be a cause of some cases of unexplained infertility. Male fertility has recently become a general concern after many publications reported a reduction in the number of normal spermatozoa in men over the past three decades. Thus, we are currently examining a variety of environmental factors that might inhibit the proton pump, or that might affect the development of these specialized cells in the male reproductive tract.

These studies are carried out on epithelial cells in situ and in vitro using a multidisciplinary approach: electrophysiological and microspectrofluorescence techniques are combined with cell biological studies on trafficking, regulation, and recycling membrane proteins.

References:

1. Breton, S., J.S. Smith, B. Lui, and D. Brown. 1996. Acidification of the male reproductive tract by a proton-pumping ATPase. Nature Medicine 2(4): 470-472.

2. Brown D. and S. Breton, 1996: Mitochondria-rich, proton-secreting epithelial cells (review). J. Exp. Biol.: 199: 2345-2358.

3. Brown, D., P.J. Smith, and S. Breton, 1997: Role of V-ATPase-rich cells in acidification of the male reproductive tract. J. Exp. Biol. 200 (2): 257-262.

4. Breton S., K. Hammar, P.J.S. Smith, and D. Brown. Proton secretion in the male reproductive tract: involvement of Cl--independent HCO3- transport. Am. J. Physiol. 1998; 275 (Cell Physiol. 44): C1134-C1142.

5. Breton S., R. Tyszkowski, I. Sabolic, and D. Brown. Postnatal development of H+ATPase (proton-pump)-rich cells in rat epididymis. Histochem. Cell Biol. 1999; 111: 97-105.

6. Jensen L., B.M. Schmidt, U. Berger, N.N. Nsumu, W.F. Boron, M.A. Hediger, D. Brown, and S. Breton. Localization of sodium bicarbonate co-transporter (NBC) protein and messenger ribonucleic acid in rat epididymis. Biol. Reprod. 1999; 60: 573-579.

7. Jensen L.J., A.K. Stuart-Tilley, L.L. Peters, S.E. Lux, S. Alper, and S. Breton, 1999: Immunolocalization of AE2 anion exchanger in rat and mouse epididymis. Biol. Reprod.: in press.

8. Brown D., I. Sabolic, and S. Breton. Membrane macro- and micro-domains in electrolyte transporting epithelia: structure-function correlations. in D.W. Seldin and G. Giebisch, editors.The Kidney: Physiology and Pathophysiology, Third edition. Raven Press, Ltd, New York; 1998. in press.