Membrane function s seminar

1. Membrane functionsseminar Dr. V. Valouskova Physiology Dept., The 2nd Medical Faculty, Prague

2. Diffusion rate J - final diffusion rate D - diffuse coefficient A - area Fick´s low (diffusion rate) J = -DA  c/ x Stokes – Einstein equilibration D = kT/(6  r ) Dc/Dx - concentration gradient (difference in concentration /thickness of membrane minus - direction of diffusion k = Boltzman`s constant T = temperature r = molecule radius  = viscosity Factors determining diffusion rate Diffusion surface (area) Concentration difference distance of diffusion size of molecules Viscosity (friction) temperature Lipid solubility Ion charge

3. fibrosis edema x η change A O2 O2 O2 CO2 x CO2 Examples of diffusion

4. Types of ion channels • Permanently opened- 2P potassium channels with 2 subunits (together with Cl- channels – resting MP) • Voltage gated – Na+,Ca2+, K+, Cl-, H+ channels- change conformation with voltage, they are opened (sometimes closed – e.g.. K+ channels in dendrites of neurons) by depolarisation, • Chemically gated – receptor-channel; ligand (receptor), mostly neurotransmitters: • receptors ionotropic- ion channel • receptor metabotropic – secondary messenger systems (G-proteins, IP3, etc.) • pHgated (pain) • mechanically gated • gated by other forms of energy– e.g.. thermal energy Paramoecium (protozoa) bangs into smt Ca+2 channels are mechanically opened - membrane depolarisation – cilia - backward movement pushes forward K+ - hyperpolarisation – speeds up forward movement

5. K+channels opened (2 subunits) - 2P-K channels – resting MP inward rectifiers(- KIR) - one direction permeable voltage-modulated (Kv) (4 subunits) voltage-dependent- 2 main levels : closed – opened gated – conformation changes K+ channel closedopened

6. Na+ channels Voltage gated Inactivated 2. Activated = opened 1. Resting = closed Epithelial Na channel (ENaC) – three subunits a, b, g. a- transfer of Na+, b a g assist to subunit a increase transport of Na+ .(i.g. in kidney - regulate ion of ECT volume, aldosteron)

7. Ionotropic ligand-gated channels Ligand opens ion channel directly i.e. acetylcholine receptor- nicotine type - channel opens when 2 molecules of ACh were bound to receptors – permeability for ionts

8. Metabotropní kanály Metabotropic ligand-gated channel Ligand opens ion channel indirectly i.e. during signal reception and signal (information) processing and storage

9. Passive - active transport facilitated diffusion [xy]1 > [xy]2 [xy]1 [xy]2 primary secondary

11. Primary active transport 3 2

12. Proton pump Difference in electrochemic potencials of protons H+(secondary of other ions) is, besides ATP, universal source of energy which cells use

13. Secondary active transport(symport, antiport) - examples Symport Na+/glukose1:1 kidney, intestine Activation – Na+ Na, K gradient -> used for transport Antiport Na+/Ca2+ 3:1 Heart Activates- kalmodulin active Antiport Na+/H+ Each cell– cell membrane Activation – level of H+ in cytosol symport sacharides, amino acids Antiport Cl - / HCO3- Erytrocyt Activation – level of HCO3- in erytrocyte

14. Transport through cell membrane(examples)

15. 1. Pancreas Langerhans cells - b cell K+channels Ca2+channels -70 mV GLUT K+channels

16. 2. Pancreas - b cell K+channels Ca2+channels -70 mV GLUT GLUCOSE K+channels

17. 3. Pancreas - b cell K+channels ATP closes channel Ca2+channels ATP -70 mV GLUT GLUCOSE K+channels

18. 4. Pancreas - b cell depolarization depolarization K+channels - - - - - - - - - Ca2+channels opened + + + + + + ATP GLUT GLUCOSE K+channels

19. 5. Ca2+ [Ca2+ ]IC Pancreas - b cell depolarization depolarization K+channels - - - - - - - - - Ca2+channels opened + + + + + + ATP GLUT GLUCOSE K+channels

20. 6. Ca2+ [Ca2+ ]IC K+channels Pancreas - b cell depolarization K+channels - - - - - - - - - Ca2+channels opened + + + + + + ATP GLUT GLUCOSE insulin

21. 7. Pancreas - b cell depolarization Ca2+ K+channels - - - - - - - - - Ca2+channels + + + + + + ATP [Ca2+ ]IC GLUT GLUCOSE K+channels (Ca+2 dependent ) insulin repolarization ( Ca +2 channels closed)

22. Pancreas Langerhans cells - b cell 8. depolarization Ca2+ K+channels - - - - - - - - - ATP dependent Ca2+channels + + + + + + voltage dependent ATP [Ca2+ ]IC GLUT GLUCOSE facilitated diffusion insulin K+channels Ca+2 dependent exocytose repolarization ( Ca +2 channels closed)

23. Proximal tubule Na+/K+ ATPase!!! 3 Na+ ATP 2 K+ PROXIMAL TUBULE lumen blood Primary urine Epithelial cell Kidney ? [Na+]in ?

24. antiport antiport symport Na++ Glu, AMK (cations) primaryactive transport - LNTP + secondaryactive transport PROXIMAL TUBULE lumen blood H+ elimination Na+/K+ ATPase !!! Na+/H+ transport (electroneutral) ATP LNTP -lumen negative transport potential Na+ resorption Active or passive transport ??

25. Na++ Glu, AMK (cations) PROXIMAL TUBULE lumen blood H+ elimination Na+/K+ ATPase !!! Na+/H+ exchange (electroneutral) ATP Na+ resorption - LNTP + Cl-resorption Cl- paracellular pathway; followed by H2O

26. Na++ Glu, AMK (cations) PROXIMAL TUBULE lumen blood H+ elimination Na+/K+ ATPase !!! Na+/H+ exchange (electroneutral) ATP Na+ resorption - LNTP + Cl-resorption Cl- paracellular pathway; followed by H2O + LPTP - LPTP -lumen positive transport potential

27. PROXIMAL TUBULE lumen blood H+ elimination Na+/K+ ATPase !!! Na+/H+ exchange (electroneutral) antiport antiport ATP Na++ Glu, AMK symport Na+ resorption - LNTP + Cl-resorption Cl- paracellular pathway; followed by H2O simple diffusion + LPTP - ?? Ca2+,Mg2+,Na+,K+ resorption Ca2+, Mg2+, Na+, K+ paracellular, followed by H2O

28. parathormon secondaryactive transport primaryactive transport PROXIMAL TUBULE lumen blood H+ elimination Na+/K+ ATPase !!! Na+/H+ exchange (electroneutral) antiport antiport ATP symport Na++ Glu, AMK Na+ resorption - LNTP + Cl-resorption Cl- paracellular pathway; followed by H2O simple diffusion + LPTP - Ca2+,Mg2+,Na+,K+ resorption Ca2+, Mg2+, Na+, K+ paracellular, followed by H2O PO43-resorption Na+/K+ ATPase Na++ Pi cotransport (secondary AT) ATP

29. Resting membrane potential = Electro-chemicequilibration mi [xi]II ~ mi = RT ln + nFD [xi]I Two parts - diffusion (osmotic) work, electric work, replacement of some amount of electric charges between 2 solutions Electro-chemical potential for the ion [xi] – ion concentration xi in solutions I a II, F - Faraday´s constant , n (or z) quantivalence of ion (e.g.. n=+1 for K+and –1 for Cl-).  electric potential in Volts, i.e. MEMBRANE POTENTIAL.

30. Origin of resting MP Membrane = demarcation line between two different environments – shift of electrically charged chemic elements - ions Membrane – resting stage - only K+ ions permeability (permeability for Cl- and Na+ non-significant) K+ ions tendency to diffuse to the place with lower concentration complementary A-(protein anions) cannot accompany K+ Potential – (charge difference) slows down K+ ions outward (Coulomb´s low) - inside - negative outside positive Osmotic power (chemic gradient) forces K+ outward (down the concentration gradient) reverse power (electric) – forces K+inward dynamic equilibration = equalizing electric and chemic gradient (electro-chemic equilibration) http://www2.biomed.cas.cz/d331/vade/

31. Nernst´s equilibration ECl = equilibration potential for Cl– R = gas constant T = absolute temperature F = Faraday`s constant(number of coulombs per mol) ZCl = quantivalence Cl– (–1) [Clo–] = concentration Cl– out, [Cli–] = concentration Cl– inside of cell

32. Goldman´s equilibration membrane potential V - membrane potential, R – gas constant, T - absolute temperature, F - Faraday constant PK+, PNa+ a PCl– permeability for K+, Na+ a Cl–, respectively [ ] concentration index i-in and o-out (intra-, extracellular concentration)

33. Hyperkalemia K+ + K+ K+ - more than 5 (10) minutes chemic gradient elektric gradient Plasma hyperkalemia resulted in membrane depolarisation. Underlying process?? Normokalemia MP - 90mV RMP - 70mV RMP - 80mV Hyperkalemia Proteins- Proteins- Proteins- K+ - - - K+ K+ K+ K+ K+ K+ K+ K+ - - - - - - + + - - - - - - - - - - New equilibrium between electric and chemic driving forces is established Membrane is DEPOLARISED - seconds to 5 (10) minutes Gradual (long-lasting) increase of [K+]e Quick experimental increase of [K+]e

34. Electric impulses in the NS • LOCAL POTENTIALS OR CURRENTS - graded, spreading with decrement • generator or receptor potentials - sensory terminals – transduction of energy i.e. mechanic or thermal to electric (graded according to the number of activated receptor cells and intensity of activation);foto-, chemo-, mechano-transduction • (post)synaptic potential (current), graded according to • - number ofexcreted quanta of neuromediators: • inhibitory (hyperpolarisation of postsynaptic membrane several ms - Cl channels) • excitatory (depolarisation – Na and/or Ca channels) • - number of active receptors (postsynaptic membrane) • 2. ACTION POTENTIALS (spikes)

35. Synaptic potential – sum of „channels“ potentials Haines, Fundamentel Neuroscience, 1997, p. 45

36. Ion membrane permeability during AP(initial segment) Action potential Na+ current inward K+ current outward permeability 1 – subthreshold depolarisation (EPSP) – K+>Na+ 2 – threshold depol. EPSP-peak – Na+ permeability = K+ permeability (open arrow) gNa g K - permeability for Na, K ions, respectively 3 – action potential (AP) 4 – subthreshold depolarisation (EPSP) – shorter latency Closed arrow –peak of AP - permeability K+ = Na+ Haines, Fundamental Neuroscience, 1997, p. 37

37. Refractory period Haines, Fundamentel Neuroscience, 1997, p. 38

38. Spontaneous neuron activity– intracellular registration out -70 mV in

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