Lecture0920final_1

Lecture0920final_1 - Typical animal cell(4 K K Na K K...

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Unformatted text preview: Typical animal cell (4) K + K + Na + K + K + Impermeant anion (e.g. amino acid, ATP 4- , phosphate K + Na + K + 10mM Na + 100 mM K + 100mM Na + 10 mM K + 110 mM anions (mostly Cl-) K+ negative “resting” membrane potential – An equilibrium will soon be established for potassium ions movement across the membrane. At this time the forces due to the concentration gradient and the membrane potential are balanced and ∆ G for the net movement of K+ ions is zero, so: ∆ V m (the memb.potential) = (RT/zF) . ln( [K + ] o /[K + ] i ) = 58mV. log 10 [K + ] o /[K + ] i (approx) = approx. -60 to -70 mV Where does that equation come from? ∆ G (net movement of K+ INTO cell) = the sum of diffusional and electrical forces driving K+ into the cell • = RT ln [K + i ]/[K + o ] + zF ∆ V m • = 0 at equilibrium So that, at equilibrium ∆ V m = RT/zF ln [K + o ]/[K + i ] •- the “Nernst equation” So for a cell with a Na/K pump that has open K + channels – a configuration typical of most resting neurons: Resting Membrane pot., ∆ V m = RT/zF ln( [K + ] o /[K + ] i ) = -60 to -70 mV – This value of ∆ V m , at which potassium ion movements are at equilibrium, is known as the “K + Equilibrium Potential” or “ the Nernst potential for K + ” – E k ∆ V m will approach E k for any cell membrane which is only (or mostly) permeable to K + •...
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Lecture0920final_1 - Typical animal cell(4 K K Na K K...

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