10/7/2011. TÁMOP–4.1.2-08/2/A/KMR-2009-0006 1 Development of Complex Curricula for Molecular Bionics and Infobionics Programs within a consortial* framework** Consortium leader PETER PAZMANY CATHOLIC UNIVERSITY Consortium members SEMMELWEIS UNIVERSITY, DIALOG CAMPUS PUBLISHER The Project has been realised with the support of the European Union and has been co-financed by the European Social Fund *** **Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben ***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg. PETER PAZMANY CATHOLIC UNIVERSITY SEMMELWEIS UNIVERSITY sote_logo.jpg dk_fejlec.gif INFOBLOKK Peter Pazmany Catholic University Faculty of Information Technology www.itk.ppke.hu (Az ideg-és izom-rendszerelektrofiziológiai vizsgálómódszerei) RICHÁRD CSERCSA, ISTVÁN ULBERTand GYÖRGY KARMOS ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEM LECTURE3 MEMBRANEPROPERTIES,RESTING POTENTIAL (Membrán tulajdonságok, nyugalmi potenciál) ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011 TÁMOP –4.1.2-08/2/A/KMR-2009-0006 3 AIMS: In this lecture, the student will become familiar with the basic electrical properties of a nerve cell. They will learn about the semi-permeable membrane, the ions producing the membrane potential, and the generation of the resting potential. www.itk.ppke.hu ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 4 During physiological operation, neurons receive input (stimuli) from other neurons. They acquire this information through synapses on their dendrites. Then they process the information. Finally they pass on the output (impulse) to other neurons through synapses on their axons. The inputs to a cell are called postsynaptic potentials (PSP). They can be excitatory (EPSP) or inhibitory (IPSP). They modify the membrane potential of the cell, thus changing its excitability. EPSPs bring the membrane potential closer to a firing threshold, IPSPs make it go farther. If the threshold is reached, an action potential is generated and that is the output of the cell. www.itk.ppke.hu NEURON AS INFORMATION PROCESSING UNIT StimulusImpulse input processingoutput ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 5 (commons.wikimedia.org) STRUCTURE OF NEURON MEMBRANE www.itk.ppke.hu ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 6 The neuron membrane is a phospholipid bilayer that separates the intracellular and the extracellular fluids. Each phospholipid molecule consists of a hydrophilic and a hydrophobic part. Molecules are organized into layers such that hydrophobic parts are inside the membrane, and hydrophilic parts contact with the external world. This structure makes the membrane not permeable for ions and charged molecules, thus a good dielectric. Certain proteins may be embedded in the membrane. They can be peripheral, if they do not span through the whole membrane, or transmembrane, if they reach both sides of the membrane. These proteins are called ion channelsand ion transportersif they can transport ions from one side of the membrane to the other. www.itk.ppke.hu STRUCTURE OF NEURON MEMBRANE ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 7 www.itk.ppke.hu phospholipidmolecule hydrophile hydrophobe phospholipidbilayer (membrane) in water good dielectric not permeable for ions, charged molecules not permeable for big molecules permeable for water and small, uncharged molecules molecules soluble in fat may dissolve in the membrane BUILDING BLOCKS OF NEURON MEMBRANE (commons.wikimedia.org) ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 8 Ions can be transported through the cell membrane passively, without energy investment, or actively, when energy is needed for the transport. The necessary energy comes from adenosine triphosphate (ATP) dephosphorylation. Ion channels can be closed, when they are in a conformation that they cannot transport ions, or open. Ion channels can be ligand gated or voltage gated, depending on the way they can become open. Ligand gated channels require certain molecules attached to them in order to open, while for voltage gated channels, a certain potential difference between the two sides of the membrane is necessary. www.itk.ppke.hu ION CHANNELS ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 9 www.itk.ppke.hu PROTEINS OF NEURON MEMBRANE phospholipidmolecule hydrophile hydrophobe (commons.wikimedia.org) ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 10 VOLTAGE-GATED NA+CHANNEL At rest (Vm= -75 mV) Immediately after depolarization (Vm= -50 mV) 5 msec after depolarization (Vm= -50 mV) extra intra Plasma membrane mgate hgate Na+ www.itk.ppke.hu OPEN INACTIVE REST ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 11 Atresting potential, them gateof thechannelis closed, thereforeNa+ ionsarenotabletoflow throughthemembrane. Whenthemembraneis depolarized(thepotentialdifferencebetweenthetwosidesof themembraneis smaller), bothgatesof thevoltage-gatedNa+ channelopen, allowingtheNa+ ionstoflow intothecell, furtherdepolarizingthemembrane. Afterthedepolarizationtheh gateof thechannelclosesfora fewmilliseconds, stoppingtheinwardflow of Na+. www.itk.ppke.hu VOLTAGE-GATED NA+CHANNEL ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 12 www.itk.ppke.hu low concentration HIGH CONCENTRATION DIFFUSION BETWEEN SPACES WITHDIFFERENT CONCENTRATION ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 13 www.itk.ppke.hu positive potential negative potential ION MOVEMENT IN ELECTRIC SPACE ions ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 14 The movement of ions through the membrane depends on • the ion concentration gradient, • electric charges. If the concentration of a certain molecule is higher in one compartment than the other, they will diffuse to the compartment with lower concentration (diffusion force). If the electric field is positive in one compartment, negative ions will tend to move there, while positive ions will move away and vice versa (electrostatic force). Furthermore, ion movement is determined also by the type of open channels. Some channels are selective for ions (e.g. only cations, or only K+ ions). www.itk.ppke.hu ION MOVEMENT ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 15 Concentration difference Electric field Ion flow Charge distribution difference Resting potential In a living cell [K+]intracell> [K+]extracelland [Na+]i< [Na+]e In a living cell at rest K+flows through the membrane much more easily than any other ions. If pK=1thenpNa=0.1. Very few ions are transported, only small changes in concentration take place. www.itk.ppke.hu ION MOVEMENT ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 16 www.itk.ppke.hu more positive charges + POTENTIAL less positive charges -POTENTIAL ION MOVEMENT THROUGH SELECTIVE CHANNEL K-channel diffusion electric force intracell extracell ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 17 Diffusion Electric field diffusion flux diffusivity concentration drift flux valence concentration velocity mobility www.itk.ppke.hu http://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Membrane_potential_ions_en.svg/1000px-Membrane_potential_ions_en.svg.png (commons.wikimedia.org) ION MOVEMENT ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 18 Ion diffusion: Electric field: No net current flow in equilibrium: Nernst equation www.itk.ppke.hu ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 19 www.itk.ppke.hu Vm = Vk= Vi-Ve Nernst equation T = 273 + 37 z = 1 F =Faradayconstant[9.649 ×104 C/mol] T = absolute temperature [K] R = gas constant[8.314 J/(mol·K)] zk= valence ci,k= intracell concentration co,k= extracell concentracion Vk=equilibriumpotential Equilibrium Vk= RT zkF ln ci,k ce,k - Vk= 61 log10 ci,k ce,k - . [mV] IDIFF + IE = Inet = 0 ion selective membrane ion concentration difference mobile +ion(K, intracell) non mobile –ion(A, intracell) - . Vk= 61 log10(24) ci,K = 120mmol/l ce,K = 5mmol/l VK = -84.19mV Vm: membrane potential NERNST EQUILIBRIUM diffusion electric force intracell extracell Ve Vi ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 20 For an excitable cell, a dielectric membrane and ion concentration difference on its two sides are essential. Resting membrane potential is the membrane potential (the potential difference between the two sides of the membrane) when there is no net ion movement. It is an equilibrium state when the sum of diffusion and electrostatic forces is zero. It also means there is no net current flow through the membrane. The Nernst equation gives the equilibrium potential of an ion, given its intra-and extracellular concentrations. This is the potential when there is no net movement of that ion. This value is proportional to the logarithm of the quotient of concentrations. www.itk.ppke.hu NERNST EQUILIBRIUM ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 21 www.itk.ppke.hu OSMOTIC CATASTROPHE Due to high concentration of ions inside the cell, water would diffuse into the cell until it bursts. ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 22 www.itk.ppke.hu NaCl in the extracell space! ion selective membrane ion concentration difference mobile +ion(K, intracell) non mobile –ion(A, intracell) mobile –ion(Cl, extracell) non mobile +ion(Na, extracell) compensated for water diffusion: ci=ce ci,K=ce,Clce,K=ci,Cl VD = VCl= VK= Vm= Vi-Ve VD= 61 log10 ci,K+ ce,Cl ce,K + ci,Cl - . [mV] VD= VK = VCl= Vm = -84.19mV Equilibrium IDIFF + IE = Inet = 0 COMPENSATE FOR THE DIFFUSION OF WATER ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 23 www.itk.ppke.hu ion selective membrane ion concentration difference mobile +ion(K, intracell) non mobile –ion(A, intracell) mobile –ion(Cl, extracell) non mobile +ion(Na, extracell) compensated for water diffusion different permeability of ion channels active transport for maintaining ion gradient (Na/K pump) no equilibriumon ion channels (leak) REALISTIC CELL MODEL ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) TÁMOP –4.1.2-08/2/A/KMR-2009-0006 24 www.itk.ppke.hu ion intra [mmol/l] extra [mmol/l] Vk Na+ 15 150 +61 mV K+ 120 5 -84.19 mV Cl- 7.5 125 -74.53 mV ion permeability, P [cm/sec] Na+ 0.05 x 10-7 K+ 1 x 10-7 Cl- 0.1 x 10-7 Vr= -61.15 mV Goldman-Hodgkin-Katz equation PK> PCl> PNa Vr= 61 log10 PK.ci,K+ PNa.ci,Na + PCl.ce,Cl - . [mV] PK.ce,K+ PNa.ce,Na + PCl.ci,Cl Depolarization: Vm>Vr Hyperpolarization: VmVr Hyperpolarization: VmPCl>PNa SUMMARY ELECTROPHYSIOLOGICAL METHODS FOR THE STUDY OF THE NERVOUS-AND MUSCULAR-SYSTEMELECTROENCEPHALOGRAPHY (EEG) 10/7/2011. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 31 www.itk.ppke.hu ions in dynamic balance, no real equilibrium, leaky channels leak compensated by energy demandingpumps/transporters(Na-K pump) Goldman equation gives good approximation for resting potential depolarization Vm>Vr, hyperpolarization Vm