FUNCTION: Testis-specific potassium channel activated by both intracellular pH and membrane voltage that mediates export of K+. May be involved in sperm capacitation and/or the acrosome reaction, essential steps in fertilization where changes in both intracellular pH and membrane potential are known to occur. In contrast to KCNMA1/SLO1, it is not activated by Ca2+ or Mg2+. Subcellular location: Membrane; Multi-pass membrane protein Tissue specificity: Testis-specific. Mainly expressed in spermatocytes. Detected in brain and brainstem, in vestibular and oculomotor nuclei, the medial nucleus of the trapezoid in the auditory system, inolfactory bulb, red nucleus, and deep cerebellar nuclei. Detected in thalamus, substantia nigra, and amygdala (at protein level). Highly expressed in the brain and kidney. Highest expression in liver, brain and spinal cord. Lowest expression in skeletal muscle. Also known as: Potassium channel subfamily T member 1, KCa4.1, SLACK.