Abstract
Extracellular purinergic agonists regulate a broad range of physiological functions via P1 and P2 receptors. Using the epididymis as a model system in which luminal acidification is essential for sperm maturation and storage, we show here that extracellular ATP and its hydrolysis product adenosine trigger the apical accumulation of vacuolar H(+)-ATPase (V-ATPase) in acidifying clear cells. We demonstrate that the epididymis can hydrolyze luminal ATP into other purinergic agonists such as ADP via the activity of nucleotidases located in the epididymal fluid and in the apical membrane of epithelial cells. Alkaline phosphatase activity and abundant ecto-5'-nucleotidase protein were detected in the apical pole of principal cells. In addition, we show that nine nucleotidase genes (Nt5e, Alpl, Alpp, Enpp1, 2, and 3, and Entpd 2, 4, and 5), seven ATP P2 receptor genes (P2X1, P2X2, P2X3, P2X4, P2X6, P2Y2, P2Y5), and three adenosine P1 receptor genes (A1, A2B, and A3) are expressed in epithelial cells isolated by laser cut microdissection (LCM). The calcium chelator BAPTA-AM abolished the apical V-ATPase accumulation induced by ATP, supporting the contribution of P2X or P2Y in this response. The PKA inhibitor myristoylated protein kinase inhibitor (mPKI) inhibited adenosine-dependent V-ATPase apical accumulation, indicating the participation of the P1 A2B receptor. Altogether, these results suggest that the activation of P1 and P2 purinergic receptors by ATP and adenosine might play a significant role in luminal acidification in the epididymis, a process that is crucial for the establishment of male fertility.