A hydrostatic model of membrane potential.

A model based on the elementary principles of hydrostatic and air pressures is proposed for classroom demonstration of some concepts related to membrane potential. The instrument comprises a system of U tubes, pressure gauges, stopcocks, and syringes. Intracellular and extracellular ionic concentrations are represented in the model by the pressure heads of fluid columns in the twin limbs of the U tubes. Membrane channels are simulated by stopcocks interposed at the bends of the U tubes. The Na(+)-K+ pump is represented by the syringes that shunt fluid from one limb of the U tube to the other. The pressure of air trapped above the fluid columns is equivalent to electrical potential.