The Measurement of Cell Capacitance in Multi-compartment Cells

1. The Measurement of Cell Capacitance in Multi-compartment Cells Arif Patel Arlene Pineda Chris Khalil

2. Membrane Capacitance • Cell membranes have a capacitive property. • Membrane capacitance (Cm) is related to cell surface area. • Cm plays a role in neuronal physiology.

3. Hypothesis • The Problem: Different methods for measuring Cm produce different results. • We propose that this difference is due to the complex anatomical structure of neurons.

4. Methodology • Three experimental techniques for measuring Cm • Current Step Method (current clamp) • Voltage Step Method (voltage clamp) • Voltage Ramp Method (voltage clamp) • Three levels of modeling to compare the measurements • Experiments were performed in crab stomatogastric neurons.

5. Current Step Method • When performed in an isopotential sphere

6. Current Step Method • When performed in multi compartment cells

7. Voltage Step Method

8. Voltage Ramp Method

9. Results of Experiments • Average Measured Capacitance for three methods: • Current Step (n=6): 23.68nF • Voltage Step (n=8): 2.87nF • Voltage Ramp (n=8):2.72nF Why are they different? Which is correct?

10. Dendrite Soma Dendrite Soma Three Models • Dual compartment attached by a resistive cable • Compartmentalized cable with added membrane • Two cylinder with compartmentalized dendrite and cable • Assumptions for model simplification: • -Ri, Rm, Cm constant • -Vr=0

11. Soma Dendrite Dendrite Soma Total Capacitance Percent Actual Capacitance=

12. IAD IAS IRD IRS IRS IAD IAD IRD Current Representation

13. Percent Actual Capacitance vs. Dendrite Diameter

14. Percent Actual Capacitance vs. Length

15. Dual Compartments w/ Compartmentalized Cable D2=.004 cm Dsoma=.004 cm Ri Ri Dendrite Soma j -1 j j +1 Rm Rm l=.06 cm Dcable=.001 cm

16. Dual Compartments w/ Compartmentalized Cable Code j j-1 j+1 Ri Ri Rm Rm Rm

17. Dendrite Soma Percent Actual Capacitance vs. Dendrite Area

18. Soma Dendrite Percent Actual Capacitance vs. Soma Area

19. Dendrite Soma Percent Actual Capacitance vs. Cable Area

20. Two Cylinders w/ Compartment Cable & Dendrite Dsoma=.004 cm Soma j -1 j j +1 jd-1 jd j j jd+1 jd+1 jd+1 l=.06 cm Dcable=.001 cm Dendrite

21. Percent Actual Capacitance vs. Dendrite Area Dendrite Soma

22. Significance of Findings • The best method for measuring cm is the current step • Voltage curve can depicts two distinct processes • Independent of morphology

23. Significance of Findings • Voltage Ramp method has provided better results than Voltage Step. • Voltage Step has provided the least reliable results • Not allowed to equalize in voltage clamp

24. Special Thanks to.. • Professor Golowasch • Professor Nadim • Professor Bose • TA’s: • Shunbing Zhao • Lakshmi Chandrasekaran