Proton and zinc effects on HERG currents

The proton and Zn2+ effects on the human ether-a-go-go related gene (HERG) channels were studied after expression in Xenopus oocytes and stable transf ection in the mammalian L929 cell line. Experiments were carried out using the two-electrode voltage clamp at room temperature (oocytes) or the whole- cell patch clamp technique at 35 degrees C (L929 cells). In oocytes, during moderate extracellular acidification (pH(o) = 6.4), current activation was not shifted on the voltage axis, the time course of current activation was unchanged, but tail current deactivation was dramatically accelerated. At pH(o) < 6.4, in addition to accelerating deactivation, the time course of a ctivation was slower and the midpoint voltage of current activation was shi fted to more positive values. Protons and Zn2+ accelerated the kinetics of deactivation with apparent K-d values about one order of magnitude lower th an for tail current inhibition. For protons, the K-d values for the effect on tail current amplitude versus kinetics were, respectively, 1.8 mu M (pK( a) = 5.8) and 0.1 mu M (pK(a) = 7.0). In the preset-ice of Zn2+ the corresp onding K-d values were, respectively, 1.2 mM and 169 mu M. In L929 cells, a cidification to pH, = 6.4 did not shift the midpoint voltage of current act ivation and had no effect on the time course of current activation; Further more, the onset and recovery of inactivation were not affected; However, th e acidification significantly accelerated tail current deactivation. We con clude that protons and Zn2+ directly interact with HERG channels and that t he interaction results, preferentially, in the regulation of channel deacti vation mechanism.