Transport of ions across plasma membranes

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Presentation transcript:

Transport of ions across plasma membranes

Electrical properties of plasma membranes

Part A: A basic en:RC circuit, superimposed on an image of a membrane bilayer to show the relationship between the two. Part B: A more elaborate en:RC circuit, superimposed on an image of a membrane bilayer. This RC circuit represents the electrical characteristics of a minimal patch of membrane containing at least one Na and two K channels. Elements shown are the transmembrane voltages produced by concentration gradients in potassium (green) and sodium (blue), The voltage-dependent ion channels that cross the membrane (variable resistors;K=green, Na=blue), the non-voltage-dependent K channel (black), and the membrane capacitance.

Nernest equation

Electro-chemical Equilibrium

Ek+

Concentration of Ions

Membrane permeability

Goldman Hodgkin Katz equation

Resting membrane potential Activity K+ channels Activity of Na+ channels Na+/K+ pumps

Na+ and K+ conductance at resting potentials

Conductance of plasma membrane (Ohm’s Law) I = ∆V/R G (conductance)= 1/R I = G. ∆V

Measuring Currents at specific membrane potential

Patch Clamp Patch still attached to the rest of the cell, as in (A), or detached, as in (B).

Patch clamp Patch Clamp electronic device is employed to maintain, or “clamp,” the membrane potential at a set value recording the ionic current through individual channels

Recording of currents in Patch Clamp

Na+ and K+ conductance at resting potentials

Changes in Resting membrane potential

Changes in Channels activity results in action potential

Ionic currents cause depolarization

Resistance to Ionic currents and activation of channels