Figure 1.

Hub-and-Spoke Circuit Model

(A) Model of a hub-and-spoke circuit (see Supplemental Experimental Procedures). β₁ and β₂ are the relative transduction strengths of spokes 1 and 2 in the presence of sensory stimuli (lightning symbols). α₁ and α₂ are the relative coupling strengths of the gap junctions connecting spokes 1 and 2 to the hub (dotted lines). $V_1^{\mathrm{\infty }}$ and $V_0^{\mathrm{\infty }}$ are the steady-state membrane potentials of spoke 1 and the hub, respectively. Arrows indicate net direction of current flow, and the magnitude of $V_0^{\mathrm{\infty }}$ is represented schematically by the size of the gray bar.

(B) When just one input is received in spoke 1 (lightning symbol), entailing an inactive spoke 2 (“2inactive”) implemented in the model by setting β₂ = 0, $V_0^{\mathrm{\infty }}$ is expected to decrease in size, as illustrated by the shortened gray bar, since current now flows in the opposite direction from the hub to spoke 2 (arrows indicate net direction of current flow).

(C) If an input is received in spoke 1 (lightning symbol) but spoke 2 is removed from the circuit altogether (“2ablated”), implemented by setting α₂ = β₂ = 0, then the model predicts less or no suppression of $V_0^{\mathrm{\infty }}$ compared to the “2inactive” condition, since current no longer leaves the hub (arrow indicates net direction of current flow).

(D) Hub steady-state membrane potential, $V_0^{\mathrm{\infty }}$, for varying α₁, α₂ and β₁ values for an inactive spoke 2 (continuous lines; derived from Equation 7 in Supplemental Experimental Procedures) or an ablated spoke 2 (dashed lines; derived from Equation 10 in Supplemental Experimental Procedures). As the plot illustrates, $V_0^{\mathrm{\infty }}$ is expected to increase with larger α₁ or smaller α₂ (fainter lines) and is always smaller when spoke 2 is present compared to when it is ablated.

(E) Spoke 1 steady-state membrane potential, $V_1^{\mathrm{\infty }}$, for varying α₁, α₂, and β₁ values for an inactive spoke 2 (continuous lines; derived from Equation 8 in Supplemental Experimental Procedures) or ablated spoke 2 (dashed lines; derived from Equation 11 in Supplemental Experimental Procedures). Spoke 1 membrane potential is expected to decrease with larger α₁ and α₂ (darker lines) and is always smaller when spoke 2 is present compared to when it is ablated.