OBJECTIVES 1. 1.Electrical components, current, voltage, resistance, conductance, capacitance Principle of equilibrium Osmolarity vs. tonicity: how they affect cell volume 4. 4.Principle behind the following equations: Nernst equation Hodgkin/Huxley equation Gibbs-Donnan Equilibrium 5. 5.Measurement of membrane conductance : Current clamp conditions Voltage clamp conditions Patch clamp conditions Review - Weeks 1 & 2

Direction of current [ ] [  ] [  ][  ][  ] [ ] [  ] [  ][  ][  ]  [  ] [ ] [  ][  ][  ] [  ] [ ] [  ][  ][  ]  [  ] [  ] [ ][  ][  ] [  ] [  ] [ ][  ][  ]  [  ] [  ] [  ][ ][  ] [  ] [  ] [  ][ ][  ]  [  ] [  ] [  ][  ][  ][  ] [  ] [  ][  ][  ]

CAPACITANCE NON-CONDUCTIVE ELEMENT A B

RC CIRCUIT V in V out RC

DIFFUSION EQUILIBRIUM B A 0.1 M K M Cl M Cl M K +

OSMOSIS BA 0.1 M K M Cl M Cl M K +

Why consider osmolarity and tonicity? [K + ] e (mM) Change in Fiber water (%) [K + ] i (mM) ↑ [K + ] e → [Na + ] e

Why consider osmolarity and tonicity? ↑ [K + ] e ↓[Na + ] e [K + ] e (mM) Change inFiber water (%) [K + ] i (mM)

ELECTROCHEMICAL GRADIENT AND EQUILIBRIUM B A 0.1 M K M Cl M Cl M K +

GIBBS-DONNAN EQUILIBRIUM BA 0.1 M K M Anions 0.1 M Cl M K +

CABLE PROPERTIES EmEm 5 STIM ∆Em ∆Em= AXON Current

Membrane / Cytosolic Resistance & Capacitance RmRiCm   cm 2   cm  F/Cm 2 Black lipid1.0 Axon (lobster) Homarus vulgaris Axon (crab) Carcinus maenas Sartorius muscle Rana pipiens