Lecture 3 - 1 BIO 317 Principles of Cellular Signaling...

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Unformatted text preview: 1 BIO 317 Principles of Cellular Signaling Lecture 3 E Na = E K = E Cl = What is the equilibrium potential for each of the permeant ions in the model cell? Model Cell 2 But.. there is only ONE membrane potential (E m )!!!!- In most cells, E m -70 mV. Thus, E m is NOT equal to the equilibrium potential of any of the permeant ions!! In model cell, E Na = +58 mV E K = -81 mV E Cl = -81 mV Equilibrium Potential What does this mean with respect to the Fux of Na + and K + through the plasma membrane? Thought Question In most cells, E Na = +58 mV E K = -81 mV E m = -70 mV 3 Effect of E m on Ion Flux E Na = 58 mV E K = -81 mV time Focus on Na + and K + Na + flux K + flux Electrical Current and Movement of Ions Across Membranes The amount of current carried by an ion through a membrane ( i ion ) is equal to ease of movement through the ion channels ( g ion ) multiplied by the driving force for diffusion for the ion ( E m-E ion ). Membrane Current Membrane Conductance Driving Force Note, in the steady state (e.g., resting membrane potential), the sum of all ionic currents is equal to zero. Assume for now that there is little or no Cl- current, then: What does this tell us about the conductances and driving forces for K + and Na + ? 4 Individual ion channels exhibit two or more conformations and behave as though they are gated (e.g., open vs. closed). Single-channel current ( i s ) is given by: i s = g s (E m-E ion ) , where g s is the single-channel conductance....
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Lecture 3 - 1 BIO 317 Principles of Cellular Signaling...

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