Voltage-Gated Ion Channels
and the
Action Potential
Voltage-Gated Ion Channels
and the
Action Potential
Electrical Signaling in the
Nervous System is
Caused by the
Opening or Closing of Ion Channels
Electrical Signaling in the
Nervous System is
Caused by the
Opening or Closing of Ion Channels
Electronically Generated Clamp Current Counterbalances the Na+ Membrane Current
Equivalent Circuit of the
Membrane
Connected to the Voltage Clamp
For Large
Depolarizations,
Both INa and IK
Are Activated
IK is Isolated By Blocking INa
INa is Isolated By Blocking IK
Vm = the Value
of the Na Battery Plus the
Voltage Drop Across gNa
gNa and gK
Have
Two Similarities and Two Differences
Voltage-Gated Na+ Channels Have Three States
Total INa is a Population Phenomenon
The Action Potential is
Generated by
Sequential Activation of gNa and gK
A Positive Feedback Cycle
Underlies the
Rising Phase of Action Potential
Slower Negative Feedback
Cycle Underlies
Falling Phase of the Action Potential
Local Circuit Flow of
Current Contributes to
Action Potential Propagation
Conduction Velocity Can be
Increased by
Increased Axon Diameter and by Myelination
Conduction Velocity Can be
Increased by
Increased Axon Diameter and by Myelination
Myelin Speeds
Up
Action Potential Conduction
Voltage-Gated Ion Channels
and the
Action Potential
Opening of Na+ and K + Channels is Sufficient to Generate the Action Potential
However, a Typical Neuron
Has Several Types of
Voltage-Gated Ion Channels
Functional Properties of
Voltage-Gated
Ion Channels Vary Widely
Voltage-Gated Ion Channels
Differ in their
Selective Permeability Properties
Functional properties of
Voltage-Gated
Ion Channels Vary Widely
Voltage-Gated K+ Channels Differ Widely in Their Kinetics of Activation and Inactivation
Functional properties of
Voltage-Gated
Ion Channels Vary Widely
Voltage-Gated Ca++ Channels Differ in Their Voltage Ranges of Activation
The Inward Rectifier K+ Channels and HCN Channels Are Activated by Hyperpolarization
Functional properties of
Voltage-Gated
Ion Channels Vary Widely
HCN Channels That Are Opened by Hyperpolarization Are Also Modulated by cAMP
Voltage-Gated Ion Channels
Belong to
Two Major Gene Superfamilies
Voltage-Gated Ion Channel Gene Superfamilies
Voltage-Gated Ion Channel Gene Superfamily
The a-Subunits of
Voltage-Gated Channels
Have Been Cloned
Four-Fold Symmetry of Voltage-Gated Channels Arises in Two Ways
P-Loops Form the
Selectivity Filter of
Voltage-Gated Cation-Permeant Channels
Ion Channels Evolve in a Modular Fashion
Modular Construction of K+ Channels