Electrophysiological Recordings Polarizable A 100 mM KCl 10 mM KCI K permselective membrane 10 mM KCI 100 mM KCI≠
V A B 100 mM KCl 10 mM KCl K+ permselective membrane I 10 mM KCl 100 mM KCl I V I V Unpolarizable electrodes Electrophysiological Recordings
a cell membrane with a specific permeability and also electrical properties channels are proteins in a lipidic environment 0 mv -90-60mV
-90/-60 mV 0 mV A cell membrane with a specific permeability and also electrical properties: channels are proteins in a lipidic environment
Resting potential Ionic equilibria RTLIK Ek=1 ZF KTI
Resting Potential • Ionic Equilibria i o K K Z E [ ] [ ] ln F RT K + + =
Nernst equation RT,KI K ZF K
Nernst equation i o K K ZF RT E [ ] [ ] K ln + + =
Neuron type Size Technique History Big cylindrical axons mm Metal electrodes K. Cole And channel concept 1940s A. Hodgkin Small myelinated axons 1-5 um Sucrose gap huxley 1950s Large neurons molluscs 500um Glass electrode Ling 1949 motoneurones 75u recording Medium size neurons <20um Hold and sample Small neurons And other cells B Sakmann 5-10um Patch-clamp And e neher And channels 1992
Big cylindrical axons And channel concept Small myelinated axons Large neurons molluscs motoneurones Medium size neurons Small neurons And other cells And Channels ~ 1mm 1-5 µm 500 µm 75 µm < 20 µm 5-10 µm Metal electrodes Patch-clamp Sucrose gap Glass electrode recording K. Cole 1940s A. Hodgkin & Huxley 1950s Hold and Sample B. Sakmann And E. Neher 1992 Neuron type Size Technique History Ling 1949
The voltage clamp membrane command
The voltage clamp I V V command membrane
1 One internal measures 2 Voltage clamp amplifier 3 When Vm is different from the command membrane potential(Vm) and is compares membrane otential, the clamp amplifier injects current connected to the voltage clamp potential to the desired into the axon through a second electrode plifier (command) potential This feedback arrangement causes the membrane potential to become the same as the command potential Measure V Command Ho voltage cla Reference amplifier electrode 4 The current flowing back into the axon, and thus Measure across its membrane current can be measured here Saline axon Current passing Recording electrode electrode
2. Electrical properties of a non-excitable cell: A resting potential leak(background channels Na/K atPase On the long term, the pump imposes Selective permeability to K+ an assymetrical ionic distribution Of the membrane imposes most of the membrane potential Cell Extracellular 140 mM K+ mmK+ 4-15Na 145Na 80/-60mV 4-30C 110Cl 0.0001Ca2+ I C t osmolarity
5 mM K+ 145 Na+ 110 Cl- 1 Ca2+ 2. Electrical properties of a non-excitable cell: A resting potential: leak (background) channels + Na+ /K+ ATPase On the long term, the pump imposes an assymetrical ionic distribution Selective permeability to K+ Of the membrane imposes most of the membrane potential 140 mM K+ 4-15 Na+ 4-30 Cl- 0.0001 Ca2+ Cell Extracellular -80/-60 mV + osmolarity
ION TRANSPORTERS ION CHANNEL urinal 2 lon transported bind Lon diffuses, across membrane through channel Ion transporters Ion channels Actively move ions against Allow ions to diffuse down concentration gradient concentration gradient -Create ion concentration -Cause selective permeability gradients to certain ions Na+/K+ ATPase Ouabain O2K. Ouabain Nat and K+ binding o binding site Outside site 000 Outside 00 Membrane COXUKCOX D Inside ATP Phosphorylatio binding ADP
Na+ /K+ ATPase
Goldman-Hodgkin-Katz equation RT PKKtl+pna[Na l+pccl I F PKK+pna[Na]+pci[cl]
Goldman-Hodgkin-Katz equation i o o o K K P [ ] P [Na ] P [Cl ] P [ ] P [Na ] P [Cl ] ln F RT V C l i K Na i K Na C l m + + − + + − + + + + =
