Identification of a novel voltage-gated Na+ channel rNa(v)1.5a in the rat hippocampal progenitor stem cell line HiB5.
A conditionally immortalised cell line, HiB5, derived from embryonic hippocampal precursor cells expressed a voltage-gated Na+ channel with electrophysiological characteristics shifted to more negative voltages and a lower sensitivity to tetrodotoxin [concentration required for half-maximal inhibition (IC50) 0.9 microM] compared with endogenous neuronal Na+ channels. The channel activation and steady-state inactivation occurred at very negative potentials with the threshold for activation at -55 mV and half-maximal inactivation at -78.7 mV. The channel was blocked by lamotrigine and sipatrigine voltage and state dependently, with potencies 5-20 times higher (IC50 12 and 1.8 microM at -80 mV respectively) than the corresponding block of endogenous Na+ channels from neurones and cloned rNa(v)1.2a (rBIIA) alpha-subunits. Both compounds slowed the channel's recovery from inactivation. Whereas lamotrigine and sipatrigine had similar effects on the fast inactivated state, the effect of sipatrigine on the slow inactivation state was more pronounced, rendering this compound overall the more effective. The molecular subtype mainly expressed by HiB5 cells was identified using RT-PCR and was a novel splice variant of rNa(v)1.5 (rNa(v)1.5a). It differs from the known rNa(v)1.5 version in that it lacks 53 amino acids in the intracellular loop between domains II and III. rNa(v)1.5a was also detected in mRNA derived from rat whole brain.
Gersdorff Korsgaard
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MP
NeuroSearch A/S, Pederstrupvej 93, 2750 Ballerup, Denmark.mgk@neurosearch.dk
Christophersen
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Ahring
P K
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Olesen
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SP
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D004594:Electrophysiology; D004622:Embryo, Mammalian; D006624:Hippocampus / Q000737:chemistry* / Q000166:cytology; D015640:Ion Channel Gating; D000077213:Lamotrigine; D008969:Molecular Sequence Data; D062554:NAV1.5 Voltage-Gated Sodium Channel; D010879:Piperazines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D015222:Sodium Channels / Q000032:analysis* / Q000235:genetics / Q000502:physiology; D013234:Stem Cells / Q000737:chemistry*; D013779:Tetrodotoxin / Q000494:pharmacology; D014227:Triazines / Q000494:pharmacology
D062554:NAV1.5 Voltage-Gated Sodium Channel; D010879:Piperazines; D011743:Pyrimidines; D012333:RNA, Messenger; C568322:Scn5a protein, rat; D015222:Sodium Channels; D014227:Triazines; D013779:Tetrodotoxin; C081980:sipatrigine; D000077213:Lamotrigine