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

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Excitable Membrane b Currents flow, so memb. potential changes h Cell membranes have passive electrical properties b h Measuring memb. potential Electrochemical Potentials (1) Chemical gradient, conc.-dependent (2) Electric potential difference b selectivity to ions 1 2 c Chemical gradient c Electromotive force (emf) Assumption b memb. is selective only to K +
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Equilibrium potential, when Chemical gradient = emf b E K , equilibrium potential of K+ in this case b 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 b b E = 2.3RT/F • log [ion] out /[ion] in Examples: 1. If [K+]out = 20mM, [K+]in = 400mM, then E K ? E
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Lecture11-2009W - Excitable Membrane Currents flow so memb...

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