Testis-specific potassium channel activated by both intracellular pH and membrane voltage that mediates export of K(+). May represent the primary spermatozoan K(+) current. In contrast to KCNMA1/SLO1, it is not activated by Ca(2+) or Mg(2+). Critical for fertility. May play an important role in sperm osmoregulation required for the acquisition of normal morphology and motility when faced with osmotic challenges, such as those experienced after mixing with seminal fluid and entry into the vagina (By similarity). Homotetramer; which constitutes the calcium-activated potassium channel. May interact with LRRC52; this interaction may change some channel gating properties, such as shifting gating to more negative potentials at a given pH. Testis-specific. The S4 segment, which is characterized by a series of positively charged amino acids at every third position, is part of the voltage-sensor. The pore-forming domain (also referred as P region) is imbedded into the membrane, and forms the selectivity filter of the pore. It contains the signature sequence of potassium channels that displays selectivity to potassium (By similarity). The RCK N-terminal domain mediates the homotetramerization, thereby promoting the assembly of monomers into functional potassium channel. The C-terminal cytosolic region confers the pH-dependence. Belongs to the potassium channel family. Calcium-activated (TC 1.A.1.3) subfamily. KCa5.1/KCNU1 sub-subfamily.