Ions Cannot Diffuse Across the Hydrophobic Barrier of the Lipid Bilayer
Ion Channels Provide a Polar Environment for Diffusion of Ions Across the Membrane
Specialized Functions of Ion Channels
Channels are Made Up of Subunits
•Ion Channels Act As Catalysts
Unlike Channels, Ion Pumps Do Not Provide a Continuous Pathway Through the Membrane
Ion Channels are Selectively Permeable
Structure of K+
Channel Has
Multiple Functional Adaptations
There are Two Major Types of Gating Actions
Gating Can Involve Conformational Changes Along the Channel Walls
Gating Can Involve Plugging the Channel
Gating Can Result from Plugging by Cytoplasmic or Extracellular Gating Particles
There are Five Types
of
Gating Controls
Binding of Exogenous Ligands Can Block Gating
Ion Permeation Can be
Prevented by
Pore Blockers
Exogenous Modulators Can Modify the Action of Endogenous Regulators
Evolution Operates More
Like a Tinkerer
Than an Engineer
Ion Channel Gene Superfamilies
Ion Channel Gene Superfamilies
Ion Channel Gene Superfamilies
Different Genes Encode
Different
Pore-Forming Subunits
Different Pore-Forming
Subunits
Combine in Various Combinations
The Same Pore-Forming
Subunits Can
Combine with Different Accessory Subunits
Alternative Splicing of Pre-mRNA
Post-Transcriptional Editing of pre-mRNA
Equivalent Circuit Model of the Neuron
The Lipid Bilayer Acts Like a Capacitor
Change in Charge Separation
Across
Membrane Capacitance is Required to Change Membrane Potential
The Bulk Solution Remains Electroneutral
Each K+ Channel Acts as a Conductor (Resistance)
Ion Channel Selectivity and Ionic Concentration Gradient Result in an Electromotive Force
An Ion Channel Acts Both as
a
Conductor and as a Battery
An Ionic Battery
Contributes to VM in Proportion to the
Membrane Conductance for that Ion
Experimental Set-up
for
Injecting Current into a Neuron
Because of Membrane
Capacitance,
Voltage Always Lags Current Flow