Fig. 3

Frequency selectivity of electrical transmission. a Equivalent circuit of a pair of coupled cells including the passive elements (resistance and capacitance, black) and active voltage-dependent conductances (INap and IK) represented as a variable resistor in series to an EMF. b Top panel, Sinusoidal current waveform of increasing frequency (ZAP protocol) is injected into cell 1 (I Cell 1) in order to test the frequency-dependent properties of electrical transmission between coupled cells. Middle, Superimposed are depicted the voltage membrane responses of the presynaptic cell (Vm Cell 1) and of the postsynaptic cell (Vm Cell 2) for a pair of coupled cells which include only passive elements (RC circuit, black elements in circuit in A). Both responses are characteristics of a low-pass filter where amplitude of membrane response decreases monotonically as sinusoidal frequency increases. Bottom, By contrast, when cells present passive and active voltage-dependent currents (IK and INap) membrane responses present certain frequency selectivity where signals close to the characteristic frequency are of bigger amplitude compared to signals whose frequency lie far from this value. c Schematic plot of the frequency transfer characteristics of electrical transmission calculated as the ratio of the FFT of the postsynaptic membrane response over the FFT of the presynaptic membrane response depicted in B, for a pair of passive cells (gray trace) and for a pair of cells which also present resonant and amplifying currents (IK and INap respectively). Whereas transfer function when cells present only passive elements show the typical profile of a low-pass filter (gray trace), the presence of voltage-dependent currents determines that transmission of signals near the characteristic frequency (vertical dashed line) is less attenuated, determining a maximum in the function (red trace). Traces are representative drawings