Changes in electrical gradients

1. Changes in electrical gradients • Electrical disequilibrium • Consequences of electrical disequilibrium • Resting membrane potential • Equilibrium potential • Membrane depolarization and hyperpolarization

2. Cell in the body are: • In chemical disequilibrium • In osmotic equilibrium • In electrical disequilibrium – few extra negative ions inside cells and their matching positive ions are outside

3. Na+ Cl- Organic Anions K+ Na+ Cl- Organic anions K+ Distribution of main ions

4. 3 Na+ Na+ Cl- Organic Anions K+ Na+ Cl- Organic anions K+ ATPase 2 K+ Anionic proteins are trapped Inside the cell Electrical disequilibrium across the cell membrane  membrane potential difference

5. How does electrical charge separation occur?

6. The cell membrane Is an insulator There are more positive charges outside and more negative charges inside

7. Na+ Cl- Organic Anions K+ Na+ Cl- Organic anions K+ Electrochemical gradient is a combination of the electrical and chemical gradients

8. Electrochemical gradient • Electrical gradients and chemical gradients across the cell membrane • Electrical force moves K+ into the cell (cell has more neg. charges) • Chemical gradient favors K+ to leave the cell (K+ concentration is low outside) • These forces reach a steady state

9. Membrane Resting Potential • The voltage difference across the cell membrane when there is an electrochemical gradient at a steady state • There is a voltage difference between the inside and the outside (potential difference)

10. The value for the resting membrane potential

11. Membrane Potential • Vm is the membrane potential (millivolts) • Resting membrane potential for nerves and muscles is -40 mV to -90 mV • The resting membrane potential is determined by K+

12. K+ channels are open during the resting membrane potential.

13. If K+ channels are open.

14. Equilibrium Potential • The membrane potential when the channels for a particular ion are open is called the equilibrium potential for that particular ion. • At EK+ the rate of ions moving in due to the electrical gradient equals the rate of ions leaving because of the concentration gradient. • EK+ is close to the resting membrane potential

15. Factors that are important for the equilibrium potential for an ion: • Only channels for that ion are open • The charge of the ion • Concentration of the ion inside the cell • Concentration of the ion outside the cell

16. At the equilibrium potential for Na+ Artificial cell, Na+ is leaving because the inside became + after the inward Movement of Na+

17. Currents during resting membrane potential K+ outward current is much stronger than Na+ inward current. Lots of K+ channels are open, few Na+ channels are open at rest.

18. Currents during resting membrane potential K+ outward current is much stronger than Na+ inward current. Lots of K+ channels are open, few Na+ channels are open at rest.

19. The value for the resting membrane potential

20. Membrane potential changes when channels open or close.

21. Changes in membrane potential • Resting membrane is polarized • Depolarization positive charges move in membrane potential moves toward 0 0 mV -70 time

22. Membrane potential changes when channels open or close.

23. Changes in membrane potential • Repolarization membrane potential returns to polarized state (+ charges leave cell) • Hyperpolarizationmembrane potential becomes more negative than at rest (extra + charges leave the cell)

24. During changes in membrane potential • Very few ions move to cause changes in membrane potential.

25. Large molecules can cross in vesicles. • Cell expends metabolic energy

26. Phagocytosis – cell engulfs a particle into a vesicle

27. Vesicular traffic across cell membranes • Endocytosis • Pinocytosis, cell engulfs extracellular fluid • Receptor-mediated endocytosis

28. Receptor mediated endocytosis LDL (which is a cholesterol carrier) is a ligand that enters by receptor mediated endocytosis

29. Exocytosis • Some molecules leave a cell by exocytosis • E.g. proteins leave cells by exocytosis

30. Integrated membrane activity during insulin secretion Resting membrane potential

31. Integrated membrane activity during insulin secretion