An inexpensive, high output voltage, voltage clamp for epithelial membranes

A circuit is described that can produce a high output voltage to automatically short-circuit an epithelial tissue mounted in an Ussing chamber. Because of its high output voltage it can short-circuit preparations requiring over 500 muA even in conjunction with high-resistance agar bridges. The circuit, which is easy to build, uses an inexpensive, low-voltage, integrated circuit operational amplifier, which is electrically isolated from the high-voltage part of the circuit by an optical isolator. The device can also be modified for use as a high impedance preamplifier for monitoring the spontaneous membrane potential.