BIO 365R Lecture 3 - Box 7-1 In the 1800s recording injury...

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Unformatted text preview: Box 7-1 In the 1800s recording injury potentials from a cut muscle showed the inside of a muscle was electrically negative Cut in the muscle Bernsteins hypothesis: resting potential is set by K + Bernstein knew that K + levels inside a muscle are high and Na + levels are low. He hypothesized that nerve and muscles cells are selectively permeable to K + at rest, and that the efflux of K + caused the resting potential. He formalized his hypothesis with the Nernst equation. Julius Bernstein (1839-1917) The squid giant axon Is the resting potential of the squid giant axon predicted by the Nernst equation? Manipulate extracellular [K + ] o , record membrane voltage (resting potential) with electrode inside axon. Plot of resting potential vs. extracellular [K + ] o (red line). Black line is the predicted resting potential if it were perfectly explained by the Nernst equation for K + ions. What if a cell is permeable to more than one ion? The Goldman-Hodgkin-Katz equation P = permeability Note: [Cl- ] in and [Cl- ] out are reversed! A mammalian neuron has the following intra- and extracellular ion concentrations: Intra (mM) Extra (mM) Na + 10 145 K + 140 5 Ca 2+ 0.0001 2 Cl- 20 110 E k = 58 1 log 5 140 E k = 58( " 1.44) = " 83.5 mV The G-H-K equation reduces to this simpler form if we ignore Cl- . Vm = 58log 5 + 145(.01) 140 + 10(.01) = 58log 6.45 140.1 = " 77.5 mV Membrane is 100x more permeable to K + than Na + Membrane is 50x more permeable to K + than Na + V m = 58log 5 + 145(.02) 140 + 10(.02) = 58log 7.9 140.2 = " 72.4 mV These are the same! V m = 58log 5 + 145(.02) 140 + 10(.02) = 58log 7.9 140.2 = " 72.4 mV V m = 58log 5(50) + 145 140(50) + 10 = 395 7010 = " 72.4 mV or Is the resting potential of the squid giant axon predicted by the Nernst equation? Manipulate extracellular [K + ] o , record membrane voltage (resting potential) with electrode inside axon. Plot of resting potential vs. extracellular [K + ] o (red line). Black line is the predicted resting potential if it were perfectly explained by the Nernst equation for K + ions. How is the ionic gradient created and maintained? There is an excess of anionic charge inside a cell due to net negative charges on nucleic acids & proteins. A Na +-K + pump (Na +-K + ATPase) moves Na + out of the cell. Since the resting membrane is only permeable to K + , it moves into the cell to replace the Na + that has been pumped out. Poisoning a squid axon with cyanide (blocks formation of ATP) stops the Na +-K + pump Addition of a source of phosphate allows a partial recovery of Na + efflux Na + efflux CN stops Na + efflux Caldwell et al. 1960 Cyanide removed Why does a process with a constant rate result in an exponential decay?...
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BIO 365R Lecture 3 - Box 7-1 In the 1800s recording injury...

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