Fig. 2.
High-frequency sine-wave techniques provide an accurate and specific assay of exocytosis from mossy fiber terminals. (A) Accuracy of ΔCm (red), ΔRa (blue), and ΔRm (green) estimates, plotted against sine-wave frequency f, for a ΔCm of 100 fF at the bouton in the morphology-based model. Model parameters were identical to those specified in the legend of Fig. 1B. (B) Predicted thermal noise of Cm estimates at a bandwidth of 5 kHz, plotted against sine-wave frequency. Noise was calculated from the complex admittance of the morphology-based model. (C) ΔCm, ΔRa, and ΔRm, measured by a 5-kHz sine-wave technique after changes in membrane capacitance ΔCm1 (Left), access resistance ΔRa1 (Center), or membrane conductance ΔGm1 (Right) in the first compartment (bouton) of the morphology-based model. (D) ΔCm, ΔRa, and ΔRm, measured by the sine-wave technique after changes in membrane capacitance (ΔCm = 100 fF; Left) and membrane conductance (ΔGm = 0.5 nS; Right) in different axonal compartments, plotted against the location of the change (x, measured from the point of emergence of the axon from the bouton). Similar calculations were performed to address three additional potential errors: (i) Errors in reversal potential setting (Erev = -50 mV instead of 0 mV); results were almost identical. (ii) Phase errors (1°); results were very similar, except for a larger ΔRa in C Center. (iii) Incomplete pipette compensation (first four cylinders of pipette model taken from ref. 59, 150 fF total pipette capacitance); results were similar except in C Left (smaller ΔRa) and C Center (larger -ΔCm).