Cellular Mechanism Underlying Hydrogen Sulfide Mediated Epithelial K(+) Secretion in Rat Epididymis

As a novel gasotransmitter, hydrogen sulfide (H(2)S) elicits various physiological actions including smooth muscle relaxation and promotion of transepithelial ion transport. However, the pro-secretory function of H(2)S in the male reproductive system remains largely unclear. The aim of this study is to elucidate the possible roles of H(2)S in modulating rat epididymal intraluminal ionic microenvironment essential for sperm storage. The results revealed that endogenous H(2)S-generating enzymes cystathionine β-synthetase (CBS) and cystathionine γ-lyase (CSE) were both expressed in rat epididymis. CBS located predominantly in epithelial cells whilst CSE expressed primarily in smooth muscle cells. The relative expression level of CBS and CSE escalated from caput to cauda regions of epididymis, which was paralleled to the progressively increasing production of endogenous H(2)S. The effect of H(2)S on epididymal epithelial ion transportation was investigated using short-circuit current (I(SC)), measurement of intracellular ion concentration and in vivo rat epididymal microperfusion. Our data showed that H(2)S induced transepithelial K(+) secretion via adenosine triphosphate-sensitive K(+) (K(ATP)) channel and large conductance Ca(2+)-activated K(+) (BK(Ca)) channel. Transient receptor potential vanilloid 4 (TRPV4) channel-mediated Ca(2+) influx was implicated in the activation of BK(Ca) channel. In vivo studies further demonstrated that H(2)S promoted K(+) secretion in rat epididymal epithelium. Inhibition of endogenous H(2)S synthesis caused a significant decrease in K(+) concentration of cauda epididymal intraluminal fluid. Moreover, our data demonstrated that high extracellular K(+) concentration actively depressed the motility of cauda epididymal sperm in a pH-independent manner. Collectively, the present study demonstrated that H(2)S was vital to the formation of high K(+) concentration in epididymal intraluminal fluid by promoting the transepithelial K(+) secretion, which might contribute to the maintenance of the cauda epididymal sperm in quiescent dormant state before ejaculation.