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 + + − + + − + + + + =