Arif_UBMTP_paper

Arif_UBMTP_paper - 1 The Measurement of Membrane...

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The Measurement of Membrane Capacitance in Multi-compartment Cells Arif Patel Math 491 Prof. Nadim, Prof. Golowasch, Prof. Bose December 18, 2006 1
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Abstract Membrane capacitance (C m ) is a fundamental property of neurons. It affects some of the electrical properties of a neuron and is indicative of the size of the cell. A major problem facing current electrophysiology research is a discrepancy in the measured value of C m of neurons provided by different methods. Different experimental techniques for measuring C m vary in the result they provide by a magnitude of an entire order. The discrepancy in the measurements may be due to the complex morphology of neurons. We used the techniques of current clamp steps, voltage clamp steps, and voltage ramp steps on intracellular recordings of stomatogastric cells of the crab Cancer borealis . We analyzed three compartmentalized models of the cell which were varied in size and shape. An evaluation of the accuracy of the three methods applied to the three models is provided here. 2
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Introduction Cell membranes are made up of a phospholipid bilayer. The phospholipid bilayer regulates the passage of material in and out of the cell. It is selectively permeable to the flow of certain molecules and ions, and thus, it tends to separate ions on its interior and exterior surfaces. This separation of charges gives cell membranes their property of capacitance. Membrane capacitance (C m ) is proportional to the surface area of a cell, which is an indicator of the size of the cell. It affects some the electrical properties of a neuron such as synaptic integration and the propagation of electrical signals. Despite the relevance of this fundamental property, there is currently no single method of measuring C m that has been proven to be accurate. Three commonly used methods of measuring C m are the methods of current step in current clamp mode and voltage step and voltage ramp in voltage clamp mode. The current step method entails charging the membrane potential by the injection of a constant amount of current into the cell. The voltage step method involves maintaining the voltage of the cell membrane at a constant value that differs from the resting potential, and voltage ramp experiments involve changing the voltage of the cell at a constant rate. The values of C m that these three methods provide vary in magnitude by an order. The problem of attaining accurate measurements of electrical parameters may be due to the neuron’s complex architecture. Neurons typically contain multiple branches of dendrites of different sizes. A complete model of a neuron entails its reconstruction, which would then be compartmentalized and matched with the appropriate parameters to simulate the cell’s electrical activity. Certain simplifications can be made to make this process easier. A common practice is to lump all of the dendrites into a single compartmentalized cylinder of finite length. A simple 3
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Arif_UBMTP_paper - 1 The Measurement of Membrane...

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