Ion Flux Flashcards
What is the major extracellular cation?
Sodium
What is the major intracellular cation?
Potassium
What is the major extracellular anion?
Chloride
________ transport is energy independent, and depends upon a downhill concentration gradient
Passive
______ transport is energy-dependent, and moves againt a concentration gradient
Active
_______ diffusion is unaided, passive transport of smaller uncharged molecules
Simple
________ diffusion is aided by transmembrane proteins required by large and/or charged molecules
This type of diffusion requires:
__________, which likely have polar core residues and allow diffusion down a concentration gradient
OR
_________, which bind a molecule on one side of the membrane and conformational change moves the molecule to the other side. The conformational change is induced by the binding event itself, or ______ hydrolysis
Facilitated
Channels
Transporters
ATP
Channels and transporters are characterized based on what 2 factors?
Directionality of molecular diffusion
Number of molecules transported (uniporter, symporter, antiporter)
Defects in the uptake system of dimeric amino acid cystine leads to the autosomal recessive disorder ___________; there are also likely to be defects in the uptake of dibasic amino acids ______, ______, and __________. This results in cystine crystals forming in the kidneys (renal calculi) identified by a positive nitroprusside test.
Patients usually present with _______ _______, or abdominal pain that comes in waves. Kidney stones are soluble in _________ urine, so they are typically dissolved by dietary changes.
Cystinuria
Arg, Lys, and ornithine
Renal colic
Alkaline
What disease is an autosomal recessive disorder caused by a defect in the transporter of nonpolar or neutral amino acids like tryptophan?
Hartnup disease
What disease manifests in infancy as failure to thrive, nystagmus, intermittent ataxia, tremor, and photosensitivity? What is another name for it?
Hartnup disease aka pellagra-like dermatosis
Tryptophan is particularly problematic in Hartnup disease. Trp is usually primarily found in the _________ and intestines. It is a precursor for serotonin, __________, and ___________ (which is a precursor for NAD)
Kidneys
Melatonin
Niacin
It has been established that a Hartnup disease “attack” is often preceded by a period of poor nutrition. Knowing this, what is the typical treatment for this disease?
A high protein diet, which can usually overcome the deficient transport of neutral amino acids
What is the difference between ligand-gated ion channels and voltage-gated ion channels?
Ligand-gated: ligand binding opens the channel by an orthosteric mechanism (ligands such as NTs or hormones)
Voltage-gated: open/close in response to changes in membrane potential; often found in neurons
In the example of neurotransmission, the neurotransmitter acts as the __________. Drugs, poisons, or therapies act as ____________ that prevent the electrochemical signal propagation. ___________ can up-regulate or down-regulate these neuronal firings.
Agonists
Antagonists
Modulators
What are the 3 possible states in which you might find a ligand-gated ion channel?
Resting (no ligand bound, channel is closed)
Open (ligand bound, channel is open)
Desensitized (ligand bound for too long, channel is closed)
Define depolarization as it relates to voltage-gated ion channels
Increased membrane potential due to influx of positively charged ions - this triggers the channel to open
What type of transport is the Na+/K+ ATPase, where is it found, and how does it maintain the intracellular environment?
And how much potassium vs. sodium per molecule of ATP?
Primary active transport
Antiporter found in ALL plasma membranes
Maintains high K+ and low Na+ in intracellular environment
[transports 2 K+ in and 3 Na+ out per ATP]
What specific transporter is involved in the primary active transport in the sarcoplasmic reticulum of muscle cells? It exists as a uniporter in MOST plasma membranes.
Ca2+ ATPase (maintains low intracellular Ca)
Describe secondary active transport
Protein assited and energy-dependent, but does not directly use ATP
It utilizes the molecular gradient established by another primary active transporter which DOES use ATP
What is the primary example of a secondary active transporter that exists as a symporter in the body?
Sodium-glucose transporter (SGLT1)
Imports 2 Na+ to transport in 1 glucose based on the sodium gradient previously established by Na+/K+ ATPase
What is the primary example of a secondary active transporter that exists as an antiporter in the body?
Na+/Ca+ exchanger (NCX) in the plasma membranes and mitochondria and ER of excitable cells
Imports 3 Na+ to remove 1 Ca++
What type of drugs are used to treat weak myocardial contractions due to conditions like CHF or MI?
Cardiotonic drugs, which inhibit the Na+/K+ ATPase and the NCX antiporter
This acts to increase myocardial intracellular Ca++, which increases the strength of cardiac muscle contraction
Describe the transport of dietary saccharides from the intestinal lumen across the enterocyte and into the bloodstream
SGLT1 transports D-glucose and D-galactose with Na+ into the intestinal epithelial cells (via secondary active transport using gradient created by Na/K pump). At the same time, GLUT5 transport fructose into the enterocyte via facilitated diffusion.
GLUT2 then transports D-glucose, D-galactose, and fructose across the cell surface to the bloodstream via facilitated diffusion
Defective transport of what ion leads to cystic fibrosis?
Cl-
Describe the clinical presentation of cystic fibrosis
Thick mucous secretion in the lungs, which leads to secondary microbial infections
Fibrosis and cysts in the pancreas due to insufficient digestive enzymes leads to failure to thrive and insulin-dependent diabetes
Describe how defective Cl- transport leads to cystic fibrosis
CFTR misfolds and never leaves the ER
Or, a defect (loss of F508) in the CFTR transmembrane protein affects Cl- transport from inside of cells to outside in the airways using ATP hydrolysis energy
The buildup of Cl- in the airway epithelial cells and sweat is compensated by an increase of Na+, water follows salt, which decreases the water content of the mucous
What are some of the complications caused by thickened mucous in cystic fibrosis patients?
Labored respiration Inflammation Scarring Continuous or recurrent infections leading to overall loss of lung function Blockage of intestines by thick feces
