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.

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

Due to a separation to a separation of charges across the membrane membrane

membrane potential Is measured in mV

Membrane Membrane has no potential ECFICF

Membrane Membrane has potential ECFICF

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

Plasma membrane A resting cell

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

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

differences in the concentration) Ionic composition ( differences in the concentration) Plasma membrane Extracellular fluid Intracellular fluid

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

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  The concept of equilibrium potential

Nernst equation for calculation of equilibrium potential (E) of any particular ion in isolation E =equilibrium potential for ion in mV C o = the concentration of the ion outside the cell in mM C I = the concentration of the ion inside the cell in mM E=61 log CoCo CICI

Nernst equation for calculation of equilibrium potential of K + in isolation E K =equilibrium potential for K + in mV = -90 mV E=61 log E=61 log E=61x-1.477

Plasma membrane ECFICF Concentration gradient for Na + Electrical gradient for Na + E Na + = +60 mV If the membrane is permeable to Na + only 150 mM /l 15 mM/l

Nernst equation for calculation of equilibrium potential of Na + in isolation E Na =equilibrium potential for Na + in mV = +60 mV E=61 log E=61 log 10 E=61x1

Plasma membrane ECF ICF Relatively large net diffusion of K + outward tend to establish an E K + 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)

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 of Na + - K + pump which exactly counterbalances the effect of diffusion of ions. RMP remains constant: passive forces = active forces At resting membrane potential

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

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

Page numbers 75 to 82 Sherwood physiology 7 th edition

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