Lecture11-2009W

# Lecture11-2009W - Excitable Membrane Currents flow so memb...

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Excitable Membrane barb2right Currents flow, so memb. potential changes head2right Cell membranes have passive electrical properties barb2right resistance & capacitance head2right Measuring memb. potential Electrochemical Potentials (1) Chemical gradient, conc.-dependent (2) Electric potential difference barb2right selectivity to ions 1 2 checkbld Chemical gradient checkbld Electromotive force (emf) Assumption barb2right memb. is selective only to K +

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3 Equilibrium potential, when Chemical gradient = emf barb2right E K , equilibrium potential of K+ in this case barb2right But, it is really steady-state (energy expenditure is required) The Nernst equilibrium : Calculating Eq. potential for single ions Chemical work (W C ) to oppose the chemical gradient W C = 2.3 RT log [K + ] out /[K + ] in Electrical work (W E ) to oppose the electrical force W E = FE (E, electrical potential difference) @ Equilibrium, W E = W C barb2right barb2right E = 2.3RT/F • log [ion] out /[ion] in Examples: 1. If [K+]out = 20mM, [K+]in = 400mM, then E K ? E K = 0.058 log (20/400) = -0.075V = -75mV 2. If [Na+]out = 460mM, [Na+]in = 50mM E Na = 0.058 log (460/50) = +0.055V = +55mV
The Goldman equation (=GHK eq.) : barb2right calculating the steady-state potential for multiple ions
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