Figure 5: HCN1 channel surface density is under-estimated in cell-attached patches.

(a) Simultaneous recording of ensemble HCN1 channel activity in a cell-attached patch (I_C-A) under whole-cell voltage-clamp (I_W-C) from the cell body of a HEK293T cell. The cell-attached pipette command voltage is shown (V_P). (b) Simultaneous recording from the same patch under whole-cell current-clamp conditions. (c) Linear relationship between the amplitude of ensemble HCN1 channel activity recorded in cell-attached patches (n=21) and as whole-cell current, under whole-cell voltage-clamp recording conditions (open symbols). Filled symbols illustrate the magnitude of ensemble HCN1 channel activity recorded from the same patches under whole-cell current-clamp conditions, and are plotted with reference to the value of whole-cell current recorded under voltage-clamp mode for each patch. Data have been fit by linear regression or with an exponential function (lines). (d, e) Pooled data show that the steady-state amplitude (d) and activation time constant (e) of ensemble HCN1 channel activity in cell-attached patches (v-c) are not significantly different (NSD) to those simultaneously recorded under whole-cell voltage-clamp (W-C v-c, n=21). In contrast, the amplitude of HCN1 channel activity recorded under whole-cell current-clamp (c-c, n=19) conditions is significantly depressed (d) and the activation time constant accelerated (e). Pooled data are presented as mean±s.e.m. and statistical significance determined with analysis of variance.