Trends in Neurosciences
Action potentials recorded with patch-clamp amplifiers: are they genuine?
Section snippets
Limitations of conventional PCAs
As the number of experimental studies10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 investigating classical excitability using PCAs in the CC mode continues to increase, we feel the need to point out some limitations of conventional PCAs used in the CC mode by providing evidence that recordings obtained in this way are affected by predictable and unpredictable errors, and should not be considered without some precautions.
In preliminary patch-clamp experiments, we noticed that the action potentials
PCAs introduce errors
In order to reveal the current absorption brought about by PCAs working in the CC mode and the consequences on the recorded voltage, we performed a series of experiments on a model passive circuit (Fig. 2A) simulating a cell membrane, into which a current was externally injected (Fig. 2B) to generate a fast voltage ramp. The model circuit was connected to various PCAs (each kept in the CC mode with the command current, Icom, at zero), and Vout and Iout were recorded. Under such conditions, an
Proposed solution
The best way of overcoming the problem would be to make a radical modification of the headstage of the PCA for CC functioning, as has been done with a PCA developed and built in our department and used in various physiological research studies21, 22, 23, 24, 25. This headstage (Fig. 4A) accomplishes the high input impedance of voltage followers (used in classical microelectrode amplifiers) by suitably connecting the two amplifying elements of a typical I–V C headstage with a ‘voltage-series’
Acknowledgements
The authors are indebted to A. Ferroni, G. Avanzini, S. Franceschetti and M. de Curtis for their support, and to G. Mostacciuolo who built and tested the new headstage in the electronic shop of the Laboratory of Electrophysiology. This work was supported by grants from Consiglio Nazionale delle Ricerche (CNR, Finalized Project ACRO), Ministero dell'Universitá e della Ricerca Scientifica e Tecnologica (MURST), and the Paolo Zorzi Foundation for Neurosciences.
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