Primary structure, functional characterization and developmental expression of the ascidian Kv4-class potassium channel.
Ascidians belong to the primitive chordates and their larvae show symmetrical beating of the tail, which is reminiscent of the swimming pattern in primitive vertebrates. Since ascidian larva contains only a small number of neurons in their entire larval nervous system, they will potentially provide a simple model for the study of animal locomotion. In a step towards the goal of establishing the molecular basis underlying ascidian larval neurophysiology, we describe here a Kv4 class of voltage-gated potassium channel, TuKv4, from Halocynthia roretzi. Whole mount in situ hybridization indicates that TuKv4 is expressed in most of larval neurons including motor neurons. TuKv4-currents reconstituted in Xenopus oocytes show currents with similar properties to the lower-threshold A-type currents from cleavage-arrested ascidian blastomeres of neural lineage. However, the voltage-dependency of the steady-state inactivation and activation was shifted leftward by 20 mV, as compared with native A-type currents, suggesting that other components may be required to restore full function of the Kv4 channel. Unexpectedly, another isoform lacking C-terminal cytoplasmic region was also isolated. This truncated isoform did not lead to a functional current in Xenopus oocytes. RT-PCR analysis showed that the truncated form is transiently expressed during larval development, suggesting some developmental role for potassium channel expression.
Nakajo
Koichi
K
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Katsuyama
You
Y
Ono
Fumihito
F
Ohtsuka
Yukio
Y
Okamura
Yasushi
Y
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001757:Blastomeres / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000502:physiology; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D007814:Larva / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology*; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010957:Plasmids; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000096:biosynthesis* / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051672:Shal Potassium Channels; D014561:Urochordata / Q000033:anatomy & histology / Q000378:metabolism*; D014981:Xenopus
D018076:DNA, Complementary; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051672:Shal Potassium Channels; D011188:Potassium