Comparison of neuronal erg current measured in embryonic rhombencephalon neurones with erg currents in CHO cells after expression of different erg channel subunits, recorded with identical solutions and pulse protocols (see pulse diagram). A, E-4031-sensitive currents recorded in a rhombencephalon neurone. Families of erg currents measured after heterologous expression of erg1a (B), erg1b (C), erg2 (D) and erg3 (E) channels in CHO cells. F, means of the normalized peak tail current amplitudes of erg currents recorded in rhombencephalon neurones (•; n= 55), as well as of erg1a (○; n= 6), erg1b (▵; n= 8), erg2 (▿, n= 10) and erg3 (□; n= 5) currents in CHO cells plotted versus the test pulse potential. Data were fitted with a single Boltzmann function. The mean values for V1/1 and the slope factor k of the individual Boltzmann functions are collected in Table 1.