Figure 1. Transient Na⁺ currents (I_NaT) in granule cells (GCs) in situ.

A and B, the properties of the I_NaT recorded in two typical GCs (cell C4120 in A, and cell C4129 in B, representative of 60 and 12 cells, respectively). The voltage-clamp protocol applied to activate I_NaT is shown in the upper part of Aa and Ba. The middle part of the panels shows the experimental tracings thus obtained in control conditions (the tracings recorded at −75 to −30 mV, and at −25 to +20 mV, have been split in two different subpanels). The lower part of the panels shows the tracings recorded in the presence of 1 μm tetrodotoxin (TTx). Aa, example of the currents recorded in group 1 neurones (see the text), in which an unclamped and a well-clamped I_NaT component were apparent. The arrow points to the prominent lag preceding the activation of the unclamped component at its threshold. Ba, example of the currents recorded in group 2 neurones (see the text), in which the well-clamped I_NaT component was observed in isolation. Ab and Bb, current–voltage (I–V) relationships for I_NaT peak amplitude in the same two cells.