Vandenberg_Lec4_2009

Vandenberg_Lec4_2009 - Today Voltage-Dependent Membrane...

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1 Voltage-Dependent Membrane Permeability 10/7/09 Today: Membrane currents & the voltage clamp technique: – Which ion channels are open during the action potential? – Can ion channels detect changes in membrane voltage? Voltage Clamp Recording Goal: to control the membrane potential & simultaneously measure ionic currents. Why? Allows researcher to determine: a) Which types of ion channels are open or closed b) When they open c) How they respond to voltage Voltage Clamp Recording
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2 Method: 1. Measure the membrane potential V m 2. Measure difference between the membrane potential and the desired (command) potential 3. Feedback amplifier passes current (I) into the axon that is proportional to this difference. This makes V m = V command 4. Measure the current. I into axon = I across membrane What is current? What is voltage? Which way does current flow? Examples: 1. Cell has only K channels; [K] o = [K] in 2. Cell has only K channels; [K] o < [K] in 3. Cell has only Na channels; [Na] o > [Na] in Ohm’s Law Current = Conductance x Driving Force (movement of + charge) I = G ( V - E equil ) Units: Current
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