The Measurement of Cell Capacitance in Multicompartment Cells

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

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

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

Methodology o Three experimental techniques for measuring Cm n n n o o 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. 4

Current Step Method o When performed in an isopotential sphere 5

Current Step Method o When performed in multi compartment cells 6

Voltage Step Method 7

Voltage Ramp Method 8

Results of Experiments o Average Measured Capacitance for three methods: n n n Current Step (n=6): 23. 68 n. F Voltage Step (n=8): 2. 87 n. F Voltage Ramp (n=8): 2. 72 n. F Why are they different? Which is correct? 9

Three Models 1) Dual compartment attached by a resistive cable 2) Compartmentalized cable with added membrane 3) Dendrite Soma Two cylinder with compartmentalized dendrite and cable Dendrite Soma Assumptions for model simplification: -Ri, Rm, Cm constant -Vr=0 10

Total Capacitance Percent Actual Capacitance= Soma Dendrite Soma 11

Current Representation IAD IAS IRS IRD IAD 12

Percent Actual Capacitance vs. Dendrite Diameter 13

Percent Actual Capacitance vs. Length 14

Dual Compartments w/ Compartmentalized Cable D 2=. 004 cm Dsoma=. 004 cm Ri Soma j -1 j Ri j +1 Dendrite Rm Rm l=. 06 cm Dcable=. 001 cm 15

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

Percent Actual Capacitance vs. Dendrite Area Soma Dendrite 17

Percent Actual Capacitance vs. Soma Area Soma Dendrite 18

Percent Actual Capacitance vs. Cable Area Soma Dendrite 19

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

Percent Actual Capacitance vs. Dendrite Area Dendrite Soma 21

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

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

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