Membrane potentials

2. Membrane potentials

3. LECTURE TARGETS • Concept of membrane potential. • Resting membrane potential. • Contribution of sodium potassium pump in the development of membrane potential. • Contribution of sodium and potassium ions in the development of membrane potential.

4. All plasma membranes Have A membrane potential (polarized electrically) i.e., charged

5. Due to a separation of charges across the membrane Membrane potential

6. membrane potential Is measured in mV

7. Membrane ECF ICF Membrane has no potential

8. Membrane ECF ICF Membrane has potential

9. Membrane ECF ICF Remainder of fluid electrically neutral Remainder of fluid electrically neutral Separated charges responsible for potential

10. Plasma membrane A resting cell

11. MECHANISM OF DEVELOPING RMP • Role of sodium potassium pump • Role of sodium ions alone • Role of potassium ions alone • Combined effects of sodium and potassium ions

12. Effects of sodium-potassium pump on membrane potential. Direct effect indirect effect Coupling is 3k+ to 2Na + Establish k+ to Na + Concentrations across membrane Separates charge (20% of RMP) Membrane more Permeable toK+ (80% of RMP)

13. Ioniccomposition (differences in the concentration) Extracellular fluid Intracellular fluid 15 150 Plasma membrane 150 65 5

14. Figure 3.29 Page 92 ECF Na+–K+ pump (Passive) (Active) Na+ channel K+ channel (Active) (Passive) ICF

15. The concept of equilibrium potential • If membrane permeable to K+ only: • What are the forces that act on K+? • When would diffusion of K+ stops? • When diffusion stops that is equilibrium potential

16. Co E = 61 log CI Nernst equation for calculation of equilibrium potential (E) of any particular ion in isolation • E =equilibrium potential for ion in mV • Co = the concentration of the ion outside the cell in mM • CI= the concentration of the ion inside the cell in mM

17. E = 61 log 0.033 5 E = 61 log E = 61x-1.477 150 Nernst equation for calculation of equilibrium potential of K+ in isolation • EK =equilibrium potential for K+ in mV • = -90 mV

19. If the membrane is permeable to Na+ only Plasma membrane ENa+ = +60 mV ECF ICF Concentration gradient for Na+ Electrical gradient for Na+ 15 mM/l 150 mM /l

20. E = 61 log 10 150 E = 61 log E = 61x1 15 Nernst equation for calculation of equilibrium potential of Na+ in isolation • ENa =equilibrium potential for Na+ in mV • = +60 mV

21. concurrent Na &K effects on membane potential Plasma membrane ICF ECF Relatively large net diffusion of K+ outward tend to establish an EK+ of –90 mV No diffusion of A– across membrane Relatively small net diffusion of Na+ inward neutralizes some of the potential created by K+ alone Resting membrane potential = –70 mV (A– = Large intracellular anionic proteins)

22. At resting membrane potential • At rest neither K+ nor Na+ are at equilibrium. • There is continuous leakage of • K+ to outside and of Na+ to inside, • But • the concentration gradient is maintained • through continuous activity ofNa+ - K+ pump which exactly counterbalances the effect of diffusion of ions. • RMP remains constant: passive forces = active forces

23. Figure 3.29 Page 92 ECF Na+–K+ pump (Passive) (Active) Na+ channel K+ channel (Active) (Passive) ICF

24. Mechanisms of RMP • Diffusion of K+ from inside to outside • Na + - K+pump • Negatively charged proteins inside

25. Page numbers 75 to 82 Sherwood physiology 7th edition

26. Message of the day Actions speak louder than words

27. THANK YOU KEEP SMILING