Fig. 1. HERG transcripts and currents in human myoblasts. (A) Total RNA was subjected to northern blot analysis with an HERG probe. A product of expected size is present in human myoblasts maintained in proliferation medium (0 h) and after different times in differentiation medium. Myoblast fusion begins after 24 hours in differentiation medium and after 36-48 hours maximal fusion is reached (70% of the nuclei are in myotubes). Equal loading of lanes was confirmed by Methylene Blue staining. (B) Dofetilide-sensitive (5 µM) endogenous K⁺ current (subtraction of the current remaining in the presence of 5 µM dofetilide from the total K⁺ current) recorded in a fusion-competent myoblast. Whole-cell current traces were elicited in the presence or absence of dofetilide (5 µM) during 1 second steps to various potentials (ranging from -85 mV to +15 mV) from a steady holding potential of -5 mV. The current-to-voltage relationships of the current suppressed by dofetilide are represented. Currents suppressed by dofetilide were measured at the peak. The reversal potential of the recorded current was shifted by -5 mV to adjust it to E_K (-35 mV; [K⁺]_out=30 mM). Cell capacitance was 24 pF. (C) Whole-cell K⁺ currents recorded in a proliferating myoblast transfected with an HERG expression vector in the absence (triangles in the current-to-voltage relationships and `control' traces in the inset) and in the presence of 5 µM dofetilide (squares in the current-to-voltage relationships and `dofetilide' traces in the inset). Same voltage protocol as in B. Cells were co-transfected with pEGFP-N3 (Clontech) to facilitate identification of transfected cells. Cell capacitance was 18 pF.

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