Measurement of Bioelectric Current with a Vibrating Probe
Summary
The manufacture, calibration and use of non-invasive vibrating probes to measure bioelectric current in various biological systems is described.
Abstract
Electric fields, generated by active transport of ions, are present in many biological systems and often serve important functions in tissues and organs. For example, they play an important role in directing cell migration during wound healing. Here we describe the manufacture and use of ultrasensitive vibrating probes for measuring extracellular electric currents. The probe is an insulated, sharpened metal wire with a small platinum-black tip (30-35 μm), which can detect ionic currents in the μA/cm2 range in physiological saline. The probe is vibrated at about 200 Hz by a piezoelectric bender. In the presence of an ionic current, the probe detects a voltage difference between the extremes of its movement. A lock-in amplifier filters out extraneous noise by locking on to the probe’s frequency of vibration. Data are recorded onto computer. The probe is calibrated at the start and end of experiments in appropriate saline, using a chamber which applies a current of exactly 1.5 μA/cm2. We describe how to make the probes, set up the system and calibrate. We also demonstrate the technique of cornea measurement, and show some representative results from different specimens (cornea, skin, brain).
Protocol
Discussion
We describe a low cost, basic, but highly sensitive vibrating probe system for measuring non-invasively electric current in a variety of biological systems.
Possible Modifications
- If platinum/iridium electrodes (World Precision Instruments; cat # PTM23B20) are used instead of stainless steel, then the gold plating stage can be eliminated.
Applications
We have used the vibrating probe to measure electric current in: ra…
Disclosures
The authors have nothing to disclose.
Acknowledgements
We are grateful to Professor Richard Borgens, Center for Paralysis Research, Purdue University, for help in assembling the vibrating probe system. This study was supported by NEI grant NIH 1R01EY019101 to MZ and BR, and in part by grants from the California Institute of Regenerative Medicine RB1-01417, NSF MCB-0951199, and by an Unrestricted Grant from Research to Prevent Blindness, UC Davis Ophthalmology.
Materials
| Material Name | Type | Company | Catalogue Number | Comment |
|---|---|---|---|---|
| Eligoy-Stainless Electrode | World Precision Instruments | SSM33A70 | 76 mm, 7 MΩ, 1-2μm tip | |
| Gold R30 connector | www.vectorelect.com | R30 | Re-usable | |
| Silver-loaded epoxy | 3M | SL65 | Mix 1-part Resin with 1-part Hardener | |
| Dissecting microscope | Olympus | SZ40 | Magnification x6 to x40 | |
| Potassium dicyanoaurate (KAu(CN)2) | Sigma-Aldrich | 379867 | CAUTION: Toxic | |
| Chloroplatinic acid hydrate (H2PtCl6 x 6H2O) | Sigma-Aldrich | 520896 | CAUTION: Toxic | |
| Lead(II) acetate trihydrate (Pb(CH3CO2)2 x 3H2O) | Sigma-Aldrich | 185191 | CAUTION: Toxic | |
| Nano-Amp power source | Made in-house | – | Powered by six 1.5 V (AAA) batteries | |
| 3-dimensional micro-positioner | Line Tool Co. | Model H | ||
| Lock-in amplifier | Stanford Research Systems | SR530 | ||
| Digital I/O interface | National instruments | PCI-6220 | ||
| Shielded Connector Block with BNC connections | National instruments | BNC-2110 | ||
| Strathclyde Electrophysiology Software | University of Strathclyde Institute of Pharmacy and Biomedical Sciences, UK | WinWCP V4.1.5 | Free download from: http://spider.science.strath.ac.uk/sipbs/software_ses.htm | |
| Calibration Chamber | Made in-house | |||
| Constant Current Calibrator | Vibrating Probe Company | Powered by one 9 V (PP3) battery |
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