The Journal of Neuroscience, May 25, 2005, ():
Specific Functions of Synaptically Localized Potassium Channels in Synaptic Transmission at the Neocortical GABAergic Fast-Spiking Cell Synapse
J. Neurosci. Goldberg et al.
25: 5230
Supplemental Data
Files in this Data Supplement:
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Figure S1. The TEA-mediated enhancement of the evoked IPSC is not due to blockade of Kv3 channels located at the FS cell soma. IPSCs were evoked by extracellular stimulation (as in Figure 1). A-B, local application of TEA near the stimulating electrode (schematic in B) had no effect on evoked IPSC amplitude (A) (control, black; TEA, gray) Note that these traces overlap. For local perfusion, we used a patch pipette (indicated in B as ‘puff’) broken under visual guidance and filled with ACSF containing 5.0 mM TEA. The pipette used for whole-cell recording (‘patch’) and the stimulating electrode (‘stim’) are indicated. C-D, local application of TEA directly to the soma of the post-synaptic pyramidal cell (and its perisomatic inhibitory inputs) reproduces the large effect of bath-applied TEA on the evoked IPSC (see Figure 1). The black arrows at the bottom of B and D indicate the direction of solution flow. E, summary data. Local application of TEA to the soma of the recorded pyramidal cell produced enhancement of the evoked IPSC (68.9 ± 14.1% increase over control) that was similar in magnitude to the effect of bath-applied TEA (see Figure 1), while local application of TEA near the stimulating electrode had no effect on evoked IPSC amplitude (100.5 ± 11.0% of control). The relative increase in IPSC amplitude produced by bath application of TEA is independent of stimulation intensity (data not shown). F-G, To confirm the success of the local application technique, we performed whole-cell current clamp recordings of FS cells located near and ≥ 100 mm away from the stimulating electrode, as in A-D. Local application of TEA in the vicinity of the stimulating electrode had no effect on an FS cell located near the pyramidal cell recorded in A-B, located ~100mM away (F), as assessed by the AP 1⁄2-width of spikes evoked in response to brief depolarizing current pulses (left), or the response to prolonged depolarizing current injection (right). In contrast, local application of TEA to the soma of an FS cell located near the pyramidal cell shown in C-D (G) produced broadening of the somatic AP and attenuation of the fast, deep AHP (left), and impaired high frequency repetitive firing (right).
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Figure S2. Voltage changes at the FS cell soma are not passively conducted to the FS cell synapse. A-B, discharge pattern of an FS cell (A) and synaptically-connected regular-spiking pyramidal cell (B) in layer II/III barrel cortex. C, brief depolarizing pulses (0.75 nA, 1.5 ms; current trace at middle) delivered to the pre-synaptic FS cell via somatic current injection elicited a somatic AP (middle) which elicited hyperpolarizing IPSPs in the post-synaptic pyramidal cell (top; shown is average of 20 sweeps). A low-chloride internal solution (ECl = -77 mV) was used for this experiment, with the pyramidal cell held at -60 mV via small positive DC current injection. D-G, after bath-application of TTX (500 nM) to block voltage-gated Na+ channels and hence active spike propagation, depolarizing somatic current injections of varying duration (D, 2 ms; E, 5 ms; F, 20 ms; G, 50 ms), did not elicit ‘on’ or ‘off’ IPSPs in the post-synaptic pyramidal cell. Longer current injections of up to 1 second (not shown) also failed to elicit IPSPs. Shown are single somatic voltage traces (middle) and the post-synaptic potential during 20 superimposed sweeps (top). Current injection was calibrated to achieve a somatic depolarization at steady-state that approximated the voltage at the peak of the action potential as in C. H, after wash-out of TTX, somatic action potentials recovered, and post-synaptic IPSPs could still be elicited. Evoked unitary IPSPs were identical in amplitude to those produced before TTX application (inset).
