S5) Regulating Flow — Ion Channels, Transporters and Electrochemical Gradients Flashcards
What are gated channels?
Gated channels are channels which open/close in response to different stimuli and control the movement of molecules both into and out of the cell
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What are ligand gated ion channels (LGIC)?
Ligand-gated ion channels are channels which open or close in response to ligand binding to a receptor site
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What are voltage gated ion channels (VGIC) ?
Voltage-gated ion channels are channels which open and close in response to the voltage potential difference across the membrane
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What is the sodium potassium pump and what does it do?
- The Na+-K+-ATPase protein in the membranes of all excitable cells ‘pumps’ 3 Na+ out of the cell and 2 K+ into the cell
- This is against the respective concentration gradients, at the expense of one ATP molecule hydrolysed
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Which secondary active transport processes are driven by the Na pump?
- Ion homeostasis
- [Ca2+]i
- Intracellular pH
- Cell volume
- Action potential
In terms of primary active transport, outline the control of resting [Ca2+]i
- PMCA expels Ca2+ out of the cell
- SERCA accumulates Ca2+ into the SR/ER
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Outline the role of the sodium-calcium exchanger (NCX)
The NCX exchanger exchanges 3 Na+ for 1 Ca2+ and so creates a net change in the electric field across the plasma membrane of 2+
- In polarised cells, Ca2+ move out of the cell, whilst Na+ move in
- In depolarised cells, NCX is inhibited to bring Ca2+ into the cell (influx)
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When cellular buffering capacity is exceeded, cellular pH is controlled by the activity of a variety of plasma membrane transporters.
Explain the role of ion transporters in intracellular pH regulation
- Acidification can be opposed by expelling H+ / the inward movement of bicarbonate ions.
- Alkalinisation is opposed by expelling HCO3- via the anion exchanger
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Different cell types use particular combinations of transporters to achieve cell volume regulation.
Explain the principles of electroneutral transport to influence water movement
- Cells extrude ions in response to cell swelling → water follows
- Cells influx ions in response to cell shrinking → water follows
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Outline the use and action of diuretic drugs to control water balance and fluid loss
Diuretic drugs are used where fluid loss is required to treat oedema or hypertension:
- Na+ reabsorption mechanism(s) are blocked
- Increased Na+ excretion to produce a hyperosmotic urine
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