1. Currents and Voltages in the Body Lecture 6 1/25/2016 1

2. Assignment 1 Read Chapter s 2 and 3 2. Read two papers and write a 1 page summary or each. 3. In some cases I have suggested papers to read as follow up to the first paper you read. 4. Monday next week we will look at some issues in setting standards 2

3. Electrical Voltages and Currents In the Body 1. The Body is an Electro Chemical System A. Basic Sources of Energy are the Metabolic Processes in the mitochondria which supply about 95% of the energy for the cell by combining O 2 with glucose to form ATP. This in turn supplies the energy for the pumps that maintain the ion gradients across membranes and generate the electric potentials of -50 to -100mV between the outside and the inside of a cell. This leads to trans membrane fields on the order of 10 7 V/m B. There are also endogenous electric fields in the extracellular fluids in the range of 10 to 100V/m 3

4. Cell Models 4

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6. Source of Electric Fields 1. Plasma membrane that defines the cell boundary and the voltage is negative on the inside. 2. The Epithelium that surrounds every organ and the skin. This leads to the Transepithelial Potential, TEP, which is positive on the inside. 3. The TEP fields move ions and molecules around and are the driving force for the growth of embryos and wound healing etc. 6

7. K+ K+-selective channels Na+ K+ Cilium Inner Segment Active transport Figure 1.1 Diagram of a single retinal rod cell illustrating the segregation of ion chan- nels that leads to the generation of a dark current. Na + channels found only in the outer segment are gated by cGMP and pass the positive inward current there. K+ channels are localized in the inner segment and pass the outward current. Photon absorbance by rho- dopsin in the outer segment triggers a transduction reaction that results in the reduction of cGMP and leads to the reduction of the inward Na+ current. 7

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9. A Cell Membrane Cartoon Voltage inside - 50 to -100mV about 1 charge per atoms 9

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11. Transepithelial Potential 1. Note separation of the Na and K channels 15-60mV 11

12. Current Densities 1. Currents across cell membranes 1 μA/cm 2 to 10 μA/cm 2 the interior of the cell is negative. 2. The Transepithelial Potential (TEP) is positive at the inside of the skin. Current densities from 10 μA /cm 2 to 100 μA /cm 2 3. Shocks at approximately 10 mA 12

13. Chick Embryos 13

14. Effects are Time Dependent Applied external currents can cause abnormalities in the neural-stage embryo stage and not Gastrula-stage At 25-75 mV/mm leads to abnormalities 14

15. Measurements Around an Chick Embryo 15

16. Currents As Function of Position 16

17. Voltage Gradients 17

18. Growth of Planarian Flatworm In an Electric Field. Wendy Beane In vivo studies show that electric fields have a lot to do in controlling the size and shape of the growth. 18

19. Amputated Limbs 10 to 100μA/cm 2 out of the cut. 60 mV/mm to start and down to 25mV/mm within 6hr (Note in other units these are Volts/meter) Growth occurs toward negative electrode. Used to guide direction of nerve growth. The currents during growth in a root or other cell can flow in one end and back into the side of the cell. We have seen effects as low as 0.2 mV across a membrane in changing the oscillation of pacemaker cells or fields of 0.01V/m Electroporation 1.5 to 3V/cell 19

20. Currents Near Wounds 20

21. Current Flow at a Cut 21

22. Electric Fields Near a Cut 22

23. Equivalent Circuit Model 23