Fig. 6.

Block of A-type ${\mathrm{K}}^{+}$ current causes stronger potentiation of $\mathrm{AP}\text{-}{\mathrm{Ca}}^{2+}$ signal in the “weaker” branch. (a1 and b1) Two layer five pyramidal neurons filled with OGB1 and AF594. (a2) Upper: current injections into the soma of the cell shown in a1 were used to initiate three APs with an interspike interval of 120 ms. Simultaneous recordings of $\mathrm{AP}\text{-}{\mathrm{Ca}}^{2+}$ signals from two sister branches (ROI 1 and 2) are aligned with the whole-cell recording (soma). Although positioned at the same path distance from the cell body, the amplitudes of two signals are quite different (hence termed strong and weak). Lower: following application of A-type channel blocker, ${\mathrm{Ba}}^{2+}$ ($200\mu \mathrm{M}$), both signals increase in amplitude. The amplitude of the first AP is now nearly identical in both branches (arrow). (b2) Same as in a2, except different cell was used (cell shown in b1). Note that the weaker branch (ROI 4) undergoes several-fold greater potentiation than the stronger branch (ROI 3). Asterisks indicate failed APs in the weaker branch. (c1) ${\mathrm{Ba}}^{2+}$-induced increase in $\mathrm{AP}\text{-}{\mathrm{Ca}}^{2+}$ amplitude, expressed as ${\mathrm{Ba}}^{2+}/\text{control ratio}$, was plotted for each of the six cells used in the study. In Cell 3, two pairs of dendrites were studied. In each cell, one pair of branches was studied, as depicted in (a1 and b1). Stronger branches are colored darker gray. Note that the relative potentiation was always stronger in a weaker branch. (c2) Same as in c1 except signal amplitudes were compared between sister branches. Note that block of A-type channels (${\mathrm{Ba}}^{2+}$) always reduced the difference between two sisters resulting in a ratio value closer to 1 (dark gray bars).