Untitled Quiz

Study Notes

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 (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.

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 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.

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.

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.