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Differentiation of electrical excitability entails changes in the currents that generate action potentials in spinal neurons of Xenopus embryos, resulting in reduced calcium entry during impulses generated at later stages of development. A dramatic increase in delayed rectifier current (I(Kv)) during the first day of development plays the major role in this process. Identification of potassium channel genes responsible for the increase in I(Kv) is critical to understanding the molecular mechanisms involved. Several members of the Shaw Kv3 gene subfamily encode delayed rectifier currents, indicating that they could contribute to the upregulation of I(Kv) that reduces the duration of action potentials. We isolated a Xenopus (x) Kv3.1 gene whose expression is restricted to the central nervous system, which is upregulated throughout the period during which I(Kv) develops in vivo. The fraction of neurons in which transcripts of this gene are detected by single-cell RT-PCR increases to 40% with time in culture, paralleling the development of I(Kv) in neurons in vitro. Expression of xKv3.1 mRNA generates a delayed rectifier potassium current in oocytes, suggesting that xKv3. 1 contributes to the maturation of I(Kv) and shortening of the action potential.

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