FIG. 7.

Developmental increase in the density of functional HCN channels at distal apical dendritic sites. A: cell-attached recording of leak-subtracted ensemble HCN channel activity evoked by a 100-mV voltage step (bottom trace). Note the increase in current amplitude and acceleration of activation kinetics with development [postnatal age is indicated, apical dendritic recordings were made at 55 (P11), 70 (P15); 15 (P26) and 30 μm (P36) from the layer 1–layer 2 border]. Leak subtraction was performed off-line by the subtraction of scaled responses generated by interleaved 20-mV voltage steps. B: summary data describing the age-dependent increase in HCN channel density with age at distal but not proximal apical dendritic sites. Each data point is represented by the smaller symbols (distal dendritic, gray; proximal dendritic, open). The number of recorded patches is indicated. Pooled data are represented by the large symbols (distal, black; proximal, gray; means ± SE). Pooled data have been fit by a bounded exponential function for distal and linear regression for proximal apical dendritic recordings. C: pooled data describing the acceleration of ensemble HCN channel kinetics with postnatal development. Each gray data point represents the kinetics of ensemble activity generated in an apical dendritic patch, approximated by a single-exponential fit to the evolution of the current, in response to a 100-mV voltage step. Large black symbols show results pooled into age groups (means ± SE). Pooled data have been fit with an exponential function (line).