Cloning and expression of the human Kv4.3 potassium channel

We report on the cloning and expression of hKv4.3, a fast inactivating. tra nsient, A-type potassium channel found in both heart and brain that is 91% homologous to the rat Kv4.3 channel. Two isoforms of hKv4.3 were cloned. On e is full length (hKv4.3 long), and the other has a 19 amino acid deletion (hKv4.3 short). RT-PCR shows that the brain contains both forms of the chan nel RNA, whereas the heart predominantly has the longer version. Both versi ons of the channel were expressed in Xenopus oocytes, and both contain a si gnificant window or noninactivating current seen near potentials of -30 to -40 mV. The inactivation curve for hKv4.3 short is shifted 10 mV positive r elative to hKv4.3 long. This causes the peak window current for the short v ersion to occur near -30 mV and the peak for the longer version to be at -4 0 mV. There was little difference in the recovery from inactivation or in t he kinetics of inactivation between the two isoforms of the channel.