Fig. 1.

Sketch of a spheroid with drain. The drain is used to impose an electric current $I^{\mathrm{e}\mathrm{x}\mathrm{t}}$ or a volumetric flow rate $Q^{\mathrm{e}\mathrm{x}\mathrm{t}}$, driving a fluid flow or current density throughout the cell spheroid. (A) Flows from inside of the spheroid to outside correspond to $Q^{\mathrm{e}\mathrm{x}\mathrm{t}},I^{\mathrm{e}\mathrm{x}\mathrm{t}}>0$. (B) Flows from outside to inside correspond to $Q^{\mathrm{e}\mathrm{x}\mathrm{t}},I^{\mathrm{e}\mathrm{x}\mathrm{t}}<0$. The pressures inside the lumen, outside the spheroid, and at the outer end of the drain are denoted $P_1^{\mathrm{e}\mathrm{x}\mathrm{t}},P_2^{\mathrm{e}\mathrm{x}\mathrm{t}}$, and $P^{\mathrm{d}}$, respectively, and correspondingly for the electric potential: $U_1^{\mathrm{e}\mathrm{x}\mathrm{t}},U_2^{\mathrm{e}\mathrm{x}\mathrm{t}}$, and $U^{\mathrm{d}}$.