KT3.2 and KT3.3, two novel human two-pore K(+) channels closely related to TASK-1

We report the cloning of human KT3.2 and KT3.3 new members of the two-pore K(+) channel (KT) family. Based on amino acid sequence and phylogenetic analysis, KT3.2, KT3.3, and TASK-1 constitute a subfamily within the KT channel mammalian family. When Xenopus oocytes were injected with KT3.2 cRNA, the resting membrane potential was brought close to the potassium equilibrium potential. At low extracellular K(+) concentrations, two-electrode voltage-clamp recordings revealed the expression of predominantly outward currents. With high extracellular K(+) (98 mM), the current-voltage relationship exhibited weak outward rectification. Measurement of reversal potentials at different [K(+)](o) revealed a slope of 48 mV per 10-fold change in K(+) concentration as expected for a K(+)-selective channel. Unlike TASK-1, which is highly sensitive to changes of pH in the physiological range, KT3.2 currents were relatively insensitive to changes in intracellular or extracellular pH within this range due to a shift in the pH dependency of KT3.2 of 1 pH unit in the acidic direction. On the other hand, the phorbol ester phorbol 12-myristate 13-acetate (PMA), which does not affect TASK-1, produces strong inhibition of KT3.2 currents. Human KT3.2 mRNA expression was most prevalent in the cerebellum. In rat, KT3.2 is exclusively expressed in the brain, but it has a wide distribution within this organ. High levels of expression were found in the cerebellum, medulla, and thalamic nuclei. The hippocampus has a nonhomogeneous distribution, expressing at highest levels in the lateral posterior and inferior portions. Medium expression levels were found in neocortex. The KT3.2 gene is located at chromosome 8q24 1-3, and the KT3.3 gene maps to chromosome 20q13.1.