Novel LQT-3 mutation affects Na+ channel activity through interactions between alpha- and beta1-subunits.
The congenital long-QT syndrome (LQT), an inherited cardiac arrhythmia characterized in part by prolonged ventricular repolarization, has been linked to 5 loci, 4 of which have been shown to harbor genes that encode ion channels. Previously studied LQT-3 mutations of SCN5A (or hH1), the gene that encodes the human Na+ channel alpha-subunit, have been shown to encode voltage-gated Na+ channels that reopen during prolonged depolarization and hence directly contribute to the disease phenotype: delayed repolarization. Here, we report the functional consequences of a novel SCN5A mutation discovered in an extended LQT family. The mutation, a single A-->G base substitution at nucleotide 5519 of the SCN5A cDNA, is expected to cause a nonconservative change from an aspartate to a glycine at position 1790 (D1790G) of the SCN5A gene product. We investigated ion channel activity in human embryonic kidney (HEK 293) cells transiently transfected with wild-type (hH1) or mutant (D1790G) cDNA alone or in combination with cDNA encoding the human Na+ channel beta1-subunit (hbeta1) using whole-cell patch-clamp procedures. Heteromeric channels formed by coexpression of alpha- and beta1-subunits are affected: steady-state inactivation is shifted by -16 mV, but there is no D1790G-induced sustained inward current. This effect is independent of the beta1-subunit isoform. We find no significant effect of D1790G on the biophysical properties of monomeric alpha- (hH1) channels. We conclude that the effects of the novel LQT-3 mutation on inactivation of heteromeric channels are due to D1790G-induced changes in alpha- and beta1-interactions.
An
R H
RH
Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
Wang
X L
XL
Kerem
B
B
Benhorin
J
J
Medina
A
A
Goldmit
M
M
Kass
R S
RS
D002460:Cell Line; D003062:Codon / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D017136:Ion Transport; D007668:Kidney; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism; D062554:NAV1.5 Voltage-Gated Sodium Channel; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism
D003062:Codon; D018076:DNA, Complementary; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568320:SCN5A protein, human; D015222:Sodium Channels; D012964:Sodium