A novel cross-species inhibitor to study the function of CatSper Ca²⁺ channels in sperm

Background and Purpose: Sperm from many species share the sperm-specific Ca²⁺ channel CatSper (cation channel of sperm) that controls the intracellular Ca²⁺ concentration and, thereby, the swimming behaviour. A growing body of evidence suggests that the mechanisms controlling CatSper activity and the role of the channel during fertilization differ among species. However, a lack of suitable pharmacological tools has hampered the elucidation of the function of CatSper. Known CatSper inhibitors exhibit considerable side effects and inhibit also Slo3, the K⁺ channel in mammalian sperm.


Experimental Approach: The drug RU1968 was reported to suppress Ca²⁺ signaling in human sperm by an unknown mechanism. We resynthesized the drug and revisited its mechanism of action in sperm form humans, mice, and sea urchins.


Key Results: We show by Ca²⁺ fluorimetry, single-cell Ca²⁺ imaging, electrophysiology, opto-chemistry, and motility analysis that RU1968 inhibits CatSper in sperm from invertebrates and mammals. The drug lacks toxic side effects in human sperm, does not affect mouse Slo3, and inhibits human Slo3 with about 15-fold lower potency than CatSper. Moreover, in human sperm, the inhibitor mimics CatSper dysfunction and suppresses motility responses evoked by progesterone, an oviductal steroid that activates CatSper. Finally, we show that the drug abolishes CatSper-mediated chemotactic navigation in sea urchin sperm.