Intracellular microelectrode measurements in small cells evaluated with the patch clamp technique

Area of Science:

• Electrophysiology
• Cellular Neuroscience
• Biophysics

Background:

• Microelectrode impalement introduces shunt resistance (Rs), causing sustained depolarization and underestimation of the true resting membrane potential (Em) in small cells.
• Fast potential transients (Ep) occurring immediately after impalement may reflect pre-impalement electrophysiological properties.

Purpose of the Study:

• To analyze microelectrode measurement equivalent circuits to determine conditions for accurately measuring pre-impalement Em using impalement transients (Ep).
• To assess the reliability of Ep as a surrogate for Em in small cells, specifically human monocytes.

Main Methods:

• Equivalent circuit analysis of microelectrode measurements.
• Simulation studies to identify optimal conditions (low microelectrode capacitance, high cell membrane capacitance).
• Whole-cell patch clamp in current clamp mode on cultured human monocytes to simultaneously monitor Em and measure Ep.

Main Results:

• Simulation indicated that low microelectrode capacitance and high cell capacitance favor Ep approximating Em.
• Experimental validation showed a correlation between Ep and Em in human monocytes.
• On average, Ep was found to be 6 mV less negative than the true Em in these small cells.

Conclusions:

• The peak of the impalement transient (Ep) can serve as a reliable indicator of the pre-impalement resting membrane potential (Em) in small cells.
• This method provides a valuable approach to overcome the limitations imposed by shunt resistance (Rs) during microelectrode recordings.
• Accurate Em measurements are crucial for understanding cellular electrophysiology, particularly in cell types like human monocytes.