voltage gated K channels Flashcards
What is the general function of potassium (K⁺) channels?
regulate membrane potential, repolarization
What are maxi-K channels (BK channels)?
large-conductance calcium-activated K⁺ channels that respond to both membrane voltage and intracellular calcium levels.
What are the main structural components of maxi-K channels?
a subunit and B subunit
calcium binding domains
What is the role of the α subunit in maxi-K channels
ion-conducting pore and contains both a voltage-sensor domain and intracellular calcium-binding sites that control the opening of the channel.
What is the role of the B subunit in maxi-K channels
enhance the channel’s calcium sensitivity, influence the channel’s voltage dependence, and regulate the kinetics of gating.
How does intracellular calcium influence maxi-K channel gating?
binds to the calcium-binding sites in the C-terminal of the α subunit, increasing the probability of channel opening even at lower voltages.
What physiological processes are maxi-K channels involved in?
neuronal firing, smooth muscle contraction, vascular tone, and neurotransmitter release by controlling membrane repolarization
How does the β1 subunit affect maxi-K channels in smooth muscle?
increases calcium sensitivity
What effect does β4 subunit expression have on neuronal maxi-K channels?
regulates excitability
What are the consequences of mutations in maxi-K channels?
hypertension, epilepsy, and cerebellar ataxia
What are TREK channels and how are they activated?
part of the two-pore domain K⁺ (K2P) family. They are mechanosensitive and activated by membrane stretch, changes in temperature, pH, and certain lipids.
What physiological role do TREK channels play?
regulate neuronal excitability, pain sensation by maintaining resting membrane potential
How do TREK channels contribute to neuroprotection?
protect neurons during conditions like ischemia and hypoxia by hyperpolarizing the membrane, reducing neuronal excitability
What are KATP channels and how are they regulated?
ATP-sensitive K⁺ channels They close when intracellular ATP levels are high and open when ATP is low, allowing K⁺ efflux to stabilize membrane potential.
What is the physiological role of KATP channels in the pancreas?
In pancreatic β-cells, KATP channels regulate insulin secretion. When ATP levels are high after glucose metabolism, KATP channels close, leading to cell depolarization and insulin release.
What are the clinical implications of KATP channel dysfunction?
neonatal diabetes, hyperinsulinism, and cardiomyopathies
What is the rationale for using KATP channel inhibitors in the treatment of type 2 diabetes?
used to stimulate insulin secretion from pancreatic β-cells.
KATP inhibitors close these channels directly, bypassing ATP-mediated regulation, resulting in increased insulin secretion to help control blood glucose levels.
What is the function of calcium-activated K⁺ channels (KCa) during the action potential?
contribute to afterhyperpolarization by allowing K⁺ outflow in response to increased intracellular calcium, which prolongs the refractory period.
How do inward rectifier K⁺ channels (Kir) stabilize the action potential?
help stabilize the resting membrane potential and facilitate slow repolarization after action potentials, contributing to the overall excitability of the neuron
