A Macintosh-based system is described for performing instrument control, data acquisition and storage operations in single-electrode whole-cell voltage clamp experiments. The system consists of a commercially available voltage clamp amplifier, multifunction input/output (I/O) board, graphical programming language (LabVIEW 2) and custom built 'virtual instrument' (VI). The I/O board is capable of fast (up to 110 ksample/s) multichannel analog-to-digital (A/D) conversion with 12-bit resolution. It can control the gain settings of the clamp unit through digital I/O lines and generate the P/N leak subtraction protocol to eliminate the linear portion of capacitive currents using analog output voltages and gating pulses. Complete voltage clamp protocols can be implemented using the on-screen front panel controls of the VI. It enables the user to visualize the acquired data, to graph sets of current-voltage (I-V) relations or to fit single-exponential functions to one current trace. To evaluate the adequacy of whole-cell recording, the total membrane capacitance (Cm), the series resistance (Rs) and the time constant (τc) of the decay of the capacitive current are calculated using the single-exponential function fit to the data. The system is particularly well suited to the study of large quantities of transmembrane I-V relationships. Source code for the crucial elements of the VI as well as sample recordings from a cultured spinal cord neuron, illustrating system operation, are presented.
Bibliographical noteFunding Information:
Supported by grants from Apple Computer Corporation to the University of Minnesota (Project MinneMac) and NIDA 04090, NIDR K15-DE-00225, ROl-DAO-1933, ROl-DA-04274 and K02-DA-00145.
- Cultured neuron
- Current-voltage relationship
- LabVIEW 2
- Leak subtraction
- Membrane current
- Voltage clamp