Testis-specific potassium channel activated by both intracellular pH and membrane voltage that mediates export of K(+) (PubMed:23129643, PubMed:24670955, PubMed:36649421, PubMed:38267364, PubMed:9452476). Represents the primary spermatozoan K(+) current. The channel underlies a pH-triggered membrane hyperpolarization during the process of sperm capacitation, as sperm encounter the alkaline environment near the ovum in the female reproductive tract, thereby playing an essential for male fertility (PubMed:34980136, PubMed:35551387, PubMed:36649421). {ECO:0000269|PubMed:23129643, ECO:0000269|PubMed:24670955, ECO:0000269|PubMed:34980136, ECO:0000269|PubMed:35551387, ECO:0000269|PubMed:36649421, ECO:0000269|PubMed:38267364, ECO:0000269|PubMed:9452476}. This is the function of KCNU1 (potassium calcium-activated channel subfamily U member 1, ENSG00000215262).