Cellular mechanisms underlying carbon monoxide stimulated anion secretion in rat epididymal epithelium

Epididymal epithelium possesses active ion transport properties conducive to the maintenance of appropriate epididymal intraluminal microenvironment. The endogenous gasotransmitter carbon monoxide (CO) regulates numerous cellular processes including water and electrolyte transport in various epithelia. However, the functional role of CO in epididymal epithelium is still elusive. This study aims to explore the potential regulatory effect of CO on transepithelial ion transport in rat epididymis. Using qPCR technique, we verified that endogenous CO synthase heme oxygenase 1 was expressed in rat caput, corpus, and cauda epididymis. In addition, endogenous CO was detected in rat cauda epididymis. Ussing chamber experiments showed that CORM-2, a CO donor, induced an increase of the short-circuit current (I_SC) in a concentration-dependent manner in rat cauda epididymal epithelium. The I_SC response could be abrogated by removing the ambient Cl^- or HCO₃^-. Interfering with the cAMP signaling pathway or blocking cystic fibrosis transmembrane regulator (CFTR) partially suppressed the CO-stimulated I_SC response. Moreover, the CO-evoked I_SC response was significantly attenuated by blocking Ca²⁺-activated Cl^- channel (CaCC) or chelating intracellular Ca²⁺. Elevation of intracellular Ca²⁺ level was also observed after CO stimulation in rat cauda epididymal epithelial cells. Collectively, this study demonstrated that CO stimulated anion secretion via activation of CFTR and CaCC in rat cauda epididymal epithelium, which might contribute to the formation of the appropriate microenvironment essential for sperm storage.