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Drug Transporters
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Terms in this set (49)
Semipermeable membrane
allows the passage of some particles while blocking the passage of others
Semipermeable membrane depends on _____.
molecule size, charge, polar or nonpolar, concentration, and needs of the cell
___________ molecules keep the bilayer flexible and stable.
cholesterol
Explain passive diffusion.
molecule moves through the bilayer from high concentration to low concentration without requiring energy (ATP) to maintain equal concentrations in and out of the cell.
Explain active transport.
the movement of ions or molecules across a cell membrane into a region of higher concentration (against the gradient), assisted by enzymes and requiring energy (ATP).
Explain facilitated diffusion.
Use transport proteins to help substances move across the cell membrane.
Facilitated diffusion is a type of ______ transport.
active
Active transport includes facilitated diffusion and vesicular transport. What are three types of vesicular transport.
exocytosis, endocytosis, budding
What particles can cross by facilitated diffusion?
4 answers
- small (monomers)
- polar (water soluble)
- charged ions (glucose, Ca2+, Cl-, Na+, K+)
- membrane transporters
Give three examples of transport proteins.
- pores
- channels
- carrier proteins
Transporters work together with drug metabolizing enzymes to impact PK and PD drug disposition. (T/F)
True
Transporter polymorphisms has important effects on ______ (in vivo/in vitro) drug pharmacokinetics.
in vivo
ATP-binding cassette (ABC) transporters
Utilize the energy of ATP hydrolysis to transport various substances; involved in tumor resistance, cystic fibrosis, bacterial multidrug resistance, and other inherited human diseases
active efflux transport (from enterocyte to the lumen or blood)
ABC transporters in the GI tract are located on ______ membrane(s).
apical and basolateral membranes
ABC transporters in the liver are located on _________ membrane(s).
canincular and sinusoidal
In the intestines, are SLC transporters used to (efflux, influx, both) molecules.
both
influx to the enterocyte; efflux into the blood (basolateral) or GI lumen (apical)
Transporters in the kidneys are predominantly located in the _____ tubule.
proximal
Canalicular membrane exports molecules to the ______. using the transporter(s).
bile; ABC and SLC
Sinusoidal membrane exports molecules to the ______ using the _____ transporter.
blood; ABC
Sinusoidal membrane imports molecules to the _____ using the _____ transporter.
hepatocyte (liver cell); SLC
Basolateral membrane exports molecules to the ______.
blood (B with B)
In the liver, drugs enter through the ______ membrane using _____ transporter.
sinusoidal (blood); SLC
ABC transporters in the kidneys are located on ________ membrane(s).
apical, leading to lumen (urine)
SLC transporters in the kidenys are located on _______ membrane(s).
basolateral (blood, influx to the proximal tubule cell) AND apical (efflux to the lumen or bile)
Apical membrane exports molecules to the ______.
GI lumen or tubule lumen (bile; kidneys)
Solute carrier (SLC) transporters
organic anion and cation transporter proteins that function as passive transporters, ion-coupled transporters, and exchange anions and cations.
efflux and influx transporters
Why is permeability important for drug absorption in the intestines?
high passive permeability limits the role of transporters in absorption. -a.k.a. allowing it to pass easily
low intrinsic permeability drugs need help from transporters to pass through
How does a high dose impact intestinal transport process?
high doses will saturate the transporters, minimizing their effect of aiding drugs to pass through into the small intestine.
The use of transporters like ABC and SLC reduce the bioavailability of the drug. (T/F)
True
Think about first pass effect. Some of the drug is lost during absorption. In this case, ABC and SLC reduce the bioavailability when they facilitate the drug into the intestines.
P-glycoprotein
a transporter protein that moves drugs out of cells and into the gut, urine, or bile
Is p-glycoprotein an influx or efflux transporter?
efflux
Can p-glycoprotein transport positively charged hydrophobic compounds?
yes
ex. antiviral, immunosuppressive, and chemo drugs
Multidrug resistance protein 2 (MRP2/ABCC2)
- apical membrane of intestines
- limit drug absorption
- transport out chemo drugs (MTX and irinotecan)
BCRP (ABCG2)
- apical membrane of intestines
- limit drug absorption
- efflux of chemo, antiviral, HMGCoA inhibitors, CCB, and steroid metabolites
PEPT1 (SLC15A1)
- apical membrane of intestines
- active ABSORPTION (influx) of dipeptides and tripeptides
- smaller peptides absorb faster and easier
- absorption of B-lactam ABX, ACEI, antiviral
Low permeability more likely to be affected by transporters. (T/F)
True
Requirements for glomerular filtration are
- small molec (MW<400)
- non-ionized
- non-protein bound
What is the clearance rate for GFR?
120 L/min
Requirements for active tubular secretion
- week acids and bases
- dependent on RPF
- requires energy input
- carrier mediated
- capacity-limited (saturable)
What is the clearance for active tubular secretion?
425 to 650 mL/min
Requirements for tubular reabsorption
- passive or active
- weak acids or bases dependent on pH of fluid in renal tubule and pKa of drug
- non-ionized
What is the clearance for tubular reabsorption
<120 mL/min
Explain the amino acid change in Arg389Gly.
At position 389, arginine was changed to glycine.
Explain the nucelotide sequence change in 1165G>C.
At nucleotide number 1165, guanine was changed to cytosine.
Follow the arrow G --> C
What kind of mutation is A355A?
synonymous (no functional change)
What kind of mutation is Arg389Gly?
missense or nonsynonymous
What kind of mutation is R389X
nonsense (premature stop codon)
What does GWAS look for?
It identifies SNPs across the genotype for a phenotype
SLOB1B1 SNP was identified by GWAS. What phenotype change does it cause?
It increases the risk of myopathy in patients with that SNP taking a statin.
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