Activation of TRPM8 promotes K⁺ secretion in rat epididymal epithelium

The epididymis establishes a unique hyper-potassium luminal microenvironment essential for sperm maturation and storage, which is largely orchestrated by epididymal epithelial ion transport. Although the transient receptor potential melastatin 8 (TRPM8) is broadly expressed across various organ systems, its physiological role in male reproduction has remained largely unexplored. This study demonstrated that TRPM8 was predominantly expressed in rat epididymal epithelial cells. Activation of TRPM8 by either the exogenous agonist WS-12 or the endogenous hormone testosterone triggered a decrease in short-circuit current (I_SC) response in primary cultured rat epididymal epithelial cells. This I_SC response was suppressed by removal of extracellular K⁺ or by pharmacological inhibition of Ca²⁺-activated potassium channels (K_Ca), Na⁺-K⁺ ATPase or the Na⁺-K⁺-Cl^- cotransporter, indicating that TRPM8 mediated transepithelial K⁺ secretion in a Ca²⁺-dependent manner. Consistently, TRPM8 activation increased intracellular Ca²⁺ concentration in primary rat epididymal epithelial cells, which could be abolished by the removal of extracellular Ca²⁺. An in vivo study showed functional TRPM8 deficiency disrupted the luminal hyper-potassium microenvironment in rat epididymis. Moreover, impaired sperm motility and reduced male fertility were observed in TRPM8-deficient rats, which could be rescued by restoring luminal hyper-potassium microenvironment through K_Ca activation. Overall, this study elucidates a crucial role for TRPM8 in establishing the epididymal hyper-potassium microenvironment, offering valuable insights into the physiological function of TRPM8 in male reproductive health and disease.