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INSTRUMENT OPERATION

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Chapter 6

Reference Section: Instrument Operation

The major topics in this section are organized alphabetically.

Bridge Mode

The Axopatch 200B may be used to follow cell membrane potential, in a way similar to the

bridge mode of conventional microelectrode amplifiers, when in current clamp (I=0,

I-CLAMP NORMAL and I-CLAMP FAST; please see Current Clamp section below).

This is possible because the series resistance compensation circuitry is operable in current

clamp, and can be used to correct for electrode resistance. Thus, with series resistance

correctly compensated in current clamp mode, the voltage at the scaled output will

accurately reflect the cell membrane potential. Changes in resting potential, spike activity,

and synaptic activity may be monitored in this way (however, please note risetime

limitations listed in the

SPECIFICATIONS

chapter for current clamp).

Compensating for electrode resistance in current clamp is straightforward. Monitor the

voltage with SEAL TEST activated or when applying a step current command; you will

note a response that reaches a steady-state level, then returns to baseline following the end

of the step. Adjust the series resistance knob so as to bring the steady-state voltage level

coincident with the baseline level. The electrode resistance is now compensated.

Capacitance Measurements

Capacitance measurements may be made in voltage-clamp mode by providing the rear-

panel capacitance dither BNC input with a time-varying TTL input to regularly activate the

Axon Axopatch 200B User Manual

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