Untitled Quiz

Ion Solvation

• Ions are surrounded by water molecules (H2O) in a process called solvation, influenced by electric charge concentration.
• As atomic radius decreases, charge concentration increases, resulting in greater solvation.
• Sodium ion (Na+) has an atomic radius of 0.095 nm, while potassium ion (K+) has a radius of 0.133 nm.
• Despite the larger atomic radius, K+ has a smaller solvation radius than Na+.

Conductance Properties

• Conductance (g) can be categorized into high and low conductance, with a linear relationship between potential difference (∆V) and the current (i) for Ohmic channels.
• Rectifying channels exhibit variable conductance, functioning better at specific membrane potentials (Vm).
• Voltage-gated ion channels are closed at resting membrane potential and open in response to membrane potential changes.

Voltage-Gated Ion Channels

• High Threshold Activation (HVA) channels (Cav1 and Cav2) activate at around -20 mV and exhibit slow inactivation.
• Low Threshold Activation (LVA) channels (Cav3) activate at -65mV to -50mV and undergo rapid inactivation.
• Ion channels maintain a membrane potential, which is the electrical potential difference across the cell membrane, typically -65mV to -70mV in mammalian cells.

Membrane Potential

• Membrane potential is generated by differences in ionic distribution across the cell membrane.
• In excitable cells, variations in membrane potential enable responses to stimuli and are critical for action potentials, facilitating nerve signal transmission and muscle contraction.
• The cell membrane creates separate intra- and extracellular solutions, each with differing ionic compositions.

Channel Structure and Function

• Na+ channels contain a voltage sensor segment (S4, rich in positive amino acids) that triggers channel opening and a selectivity filter (P region).
• The inactivation gate is located in the domain III-IV loop, which occludes the pore upon channel inactivation.
• Main types of voltage-gated Na+ channels (Nav1.1-Nav1.9) have a subunit configuration that allows for functional pore creation, contributing to action potential generation.
• Na+ channels are blocked by tetrodotoxin (TTX), feature low activation thresholds, intense ion flow, and rapid inactivation.

Other Ion Channels

• K+ channels are activated by voltage (Kv family with 12 types) and calcium ions (KCa).
• K+ channels consist of 4 identical subunits with a 6-segment single domain, showing slow inactivation kinetics that dictate the duration of repolarization during action potentials.
• Ca2+ channels are classified into three families (Cav1, Cav2, Cav3) with various isoforms, playing critical roles in cellular responses.