Lecture_09_Membrane Transport II

Membrane Transport II: Ion Channels and Membrane Potential

Cell Membrane Potential:
- Understand factors contributing to cell membrane potential.
Ion Channel Selectivity:
- Explain structural selectivity of ion channels.
Patch-Clamp Technique:
- Describe and apply the patch-clamp technique for measuring ion channel current.
Types of Gated Channels:
- Compare ligand-gated, voltage-gated, and mechanically-gated channels with examples.
Neurons Structure:
- Describe a neuron's parts and action potential generation and propagation.
Electrical to Chemical Signal Conversion:
- Steps for converting action potentials to neurotransmitter release at synapses.
Neurotransmitter Functions:
- Differentiation between excitatory and inhibitory neurotransmitters.
Optogenetics:
- Explore optogenetics as a method to study neuron activity.

Functionality:
- Ion channel proteins create hydrophilic pores for ions across membranes according to electrochemical gradients.
Ion Selectivity:
- Determined by:
  - Diameter and shape of the channel.
  - Ion-specific charged amino acids lining the channel.
Gating Mechanism:
- Ion channels are not continuously open and require specific stimuli for activation.
- Faster transport than traditional transporters, but do not utilize energy for active transport.

Key Concept:
- Membrane potential influenced by ion permeability.
Ion Distribution:
- Gradient and movement of specific ions, especially K+, contribute to resting potential.
- Typical resting potential in animal cells is between -20mV and -200mV.

Recording Ion Channel Activity:
- Involves a microelectrode that isolates a section of the membrane to trap an ion channel.
- Enables monitoring of ion flow through this channel.
Channel Behavior:
- Ion channels display an all-or-nothing behavior, alternating between open and closed states randomly.

Gating Types:
- Ion channels show variability in selectivity and gating mechanisms, influenced by:
  - Mechanical force
  - Ligand binding
  - Membrane potential.

Example: Auditory hair cells.
- Stereocilia respond to sound vibrations, leading to channel opening and ion influx.

Functionality:
- Open due to deformation in membrane structure, regulating physiological processes such as pressure and touch sensation.

Responsiveness:
- Respond to changes in membrane potential, crucial for electrical signal propagation in neurons and other cells.
- Example: Mimosa pudica’s leaf-closing response.

Neuron Structure:
- Composed of cell body, axon, and dendrites.
- Axons conduct signals away from the cell body; dendrites receive signals from other neurons.
Action Potentials:
- Initiated by sufficient stimulation, produces a wave of electrical activity along the axon, characterized as an action potential.

Role:
- Na+ Channels: Enable depolarization by opening and allowing Na+ influx.
- K+ Channels: Induce repolarization by allowing K+ efflux post-depolarization.
Conformational States:
- Na+ channels oscillate between closed, open, and inactivated states influenced by membrane potential.

Chemical Signal Transmission:
- Action potentials lead to neurotransmitter release at synapses, converting electrical signals into chemical signals.
Process:
- Arrival of action potential opens voltage-gated Ca2+ channels, Ca2+ influx induces neurotransmitter release.
Role of Neurotransmitters:
- Excitatory or inhibitory effects determined by receptor type.

Examples:
- Receptors that respond to neurotransmitters (ACh, GABA, glycine).
- Mechanism for converting chemical signals back into electrical ones at the postsynaptic membrane.

Application:
- Use of light to control neuron activity via light-gated ion channels from algae in live subjects.
Purpose:
- Facilitates detailed study of neural circuits governing behaviors.

Understanding the complex interactions of ion channels and signaling mechanisms is essential to grasp the functional dynamics of neurons and their role in signaling.