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      Aminoglycoside antibiotics restore functional expression of truncated HERG channels produced by nonsense mutations.

      Heart Rhythm

      Transfection, Analysis of Variance, Patch-Clamp Techniques, Microscopy, Confocal, metabolism, genetics, Long QT Syndrome, Humans, pharmacology, Gentamicins, Ether-A-Go-Go Potassium Channels, Codon, Nonsense, Cells, Cultured, Blotting, Western

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          Pharmacologic restoration of the trafficking defects of HERG missense mutations has been documented. However, whether correction of HERG nonsense mutations is possible is unknown. The purpose of this study was to investigate the effect of aminoglycoside antibiotics on the expression of nonsense mutants expected to produce truncated HERG channels. HERG channel and mutant currents were recorded by whole-cell patch clamp techniques. Pharmacologic rescue was applied by culturing the cells in 400 microg/mL G-418 or gentamicin for 24 hours. Current densities were significantly reduced in cells expressing R1014X and W927X mutants compared to those of cells expressing wild-type (WT) HERG. R863X and E698X mutants failed to generate any typical HERG currents. Mean peak tail current density of R1014X mutant was significantly lower than that of WT (3.9 +/- 1.4 pA/pF, n = 8, vs 47.8 +/- 6.3 pA/pF, n = 12, P <.05) and increased to 12.7 +/- 3.3 pA/pF (n = 7, P <.05) and 18.3 +/- 3.7 pA/pF (n = 8, P <.05) after G-418 and gentamicin treatment. The voltage dependence of activation of R1014X was also restored after drug treatment. Furthermore, expression of full-length proteins for R1014X induced by drugs was detected by western blot and confocal imaging. Similar results were observed in W927X. For R863X and E698X, however, gentamicin treatment had no effect. In the cells cotransfected with WT/R1014X, gentamicin and G-418 demonstrated different results: gentamicin, but not G-418, increased the current density by 2.2-fold (n = 12, P <.05). The study findings provide proof of principle that interventions designed to read through premature stop mutations may at least partially reverse the LQT2 phenotype in vitro.

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