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Calculation of time constants for intracellular diffusion in whole cell patch clamp configuration
C Oliva1, I S Cohen, R T Mathias
1Department of Physiology and Biophysics, State University of New York, Stony Brook 11794-8661.
Biophysical Journal
|November 1, 1988
Summary
This study models substance diffusion into cardiac cells, finding pipette diffusion is the main barrier to content equilibration. A simple equation estimates intracellular concentration steady-state times based on pipette geometry and substance diffusion.
Area of Science:
- Cellular physiology
- Biophysics
- Pharmacology
Background:
- Accurate intracellular concentration measurements are crucial for understanding cell function.
- The whole-cell patch clamp technique is widely used but can be limited by slow equilibration of intracellular contents.
- Diffusion dynamics within the pipette and into the cell are not fully characterized.
Purpose of the Study:
- To develop a simplified model for analyzing substance diffusion from pipettes into canine cardiac Purkinje cells.
- To identify key variables influencing the rate of intracellular content equilibration.
- To provide a tool for estimating the time required to reach a steady-state intracellular concentration.
Main Methods:
- Numerical solution of the one-dimensional diffusion equation for various pipette geometries.
- Derivation of a simplified analytic equation for predicting steady-state diffusion time.
- Analysis of the relationship between pipette geometry, solution properties, and diffusion rates.
Main Results:
- Diffusion within the pipette represents the primary limitation for achieving pipette and cellular content equilibration.
- A derived analytic equation accurately estimates the time constant for reaching steady-state intracellular concentrations.
- The time constant is dependent on a pipette geometric factor (pipette resistance/filling solution resistivity), cell volume, and the substance's diffusion coefficient.
- Pipette perfusion beyond 20 microns from the tip offers no significant advantage in reducing equilibration time.
Conclusions:
- Pipette diffusion dynamics are critical for successful whole-cell patch clamp experiments.
- The developed model and analytic equation offer a practical method for researchers to estimate and optimize experimental conditions.
- Understanding these diffusion limitations can improve the reliability and efficiency of studies involving intracellular substance delivery.