Characterization of potassium channels involved in volume regulation of human spermatozoa

Fertility depends in part on the ability of the spermatozoon to respond to osmotic challenges by regulating its volume, which may rely on the movement of K+. These experiments were designed to characterize the K+ channels possibly involved in volume regulation of human ejaculated spermatozoa by simultaneously exposing them to a physiological hypo-osmotic challenge and a wide range of K+ channel inhibitors. Regulation of cellular volume, as measured by flow cytometry, was inhibited when spermatozoa were exposed to quinine (QUI; 0.3 mM), 4-aminopyridine (4AP; 4 mM) and clofilium (CLO; 10 mu M) which suggests the involvement of voltage-gated K+ channels Kv1.4, Kv1.5 and Kv1.7, acid-sensitive channel TASK2 and the beta-subunit minK (IsK) in regulatory volume decrease (RVD). QUI and 4AP and, to some extent, CLO also induced hyper activation-like motility. A sensitivity of RVD to pH could not be demonstrated in spermatozoa to support the involvement of TASK2 channels. Western blotting indicated the presence of Kv1.5, TASK2, TASK3 and minK channel proteins, but not Kv1.4. Furthermore, Kv1.5, minK and TASK2 were localized to various regions of the spermatozoa. Although Kv1.4, Kv1.7, TASK2 and TASK3 channels may have important roles in human spermatozoa, Kv1.5 and minK appear to be the most likely candidates for human sperm RVD, serving as targets for non-hormonal contraception.