pharmacology membrane transporters

1. Membrane transporters
Dr. Prerna Singh
JR1 Department of Pharmacology

2. Channel vs transport protein
Channel Transporter
Pores in membrane through which
substance diffuse down the gradient
Transporter are proteins which
undergo conformational change to
transport substance
Passive transport Active or passive transport
Not saturable Saturable
No inhibition by substrate analogue Inhibited by substrate analogue
Turnover rate 1lacs per second to
10lac per second
Turnover rate 100 to 1000 per
second
Gates Multiple subunits

4. Mechanism of transport across
membrane
1. Passive diffusion
2. Facilitated diffusion
3. Active transport

5. Mechanism of transport across
membrane
1.Passive diffusion:
• Simple diffusion of solute
• Concentration gradient
• high to low concentration
• without any energy requirement
2.Facilitated diffusion:
• Facilitated by transporter
• Concentration gradient
• High to low concentration
• without any energy requirement

6. 3. Active transport
• Transport solute against concentration gradient
• ATP
Primary active transport: directly couples with ATP hydrolysis.
Example: ABC transporter, NA-K-ATPase pump
Secondary active transport: ion coupled
1. Symport: Example: SGLT
2. Antiport: Example: NCX

8. Membrane transport protein
• Pk Processes ADME include membrane transports
• Transporters
• Proteins
• Control influx of essential nutrients
• Control efflux of cellular waste including toxins and drugs
• 2000 i.e. 7% of human genes code for transporters.
• Two major superfamily's for drug transport
1. ABC (ATP binding cassette) transporter
2. SLC (Solute carrier) transporter

9. ABC transporters
• Primary active transporters
• Unidirectional transporters (efflux)
• Divided into 7 groups from ABCA to ABCG
• P glycoprotein (Pgp / ABCB1)
• Breast cancer resistance protein (BCRP/ABCG2)
• Cystic fibrosis transmembrane conductance regulator
(CFTR/ABCC7)

10. Mutations in ABC Transporter
• Mutations in genes for ABC transporter responsible for many
human genetic diseases
• Examples:
ABCA: Tangier Disease
 ABCC: Dubin-Johnson Syndrome and Cystic Fibrosis
ABCD: Adrenoleukodystrophy

11. ABC structure
There are two domains in ABC structure.
1. Nucleotide binding domain:
• site for ATP binding
2. Transmembrane domain:
• site recognize substrate
• undergoes conformational change
• transport substrate across membrane

12. ABC mechanism

13. Animated ABC mechanism

14. SLC transporter
• Transport substrate
• facilitated transport
• secondary active transport
• Bidirectional transporter
• 48 families of SLC
Examples: Serotonin transporter (SERT/ SLC6A4)
Dopamine transporter (DAT/SLC6A3)
Organic anion transporter 1 (OAT1/SLC22A6)
Organic anion transporter 3 (OAT3/SLC22A8)
Organic cation transporter 2 (OCT2/SLC22A2)

15. Role of SLC transporter
• Glucose absorption elimination and distribution (SLC 2, 5, 50)
• Transport of water soluble vitamins (SLC 19, 52, 46)
• Transport of zinc and iron (SLC 11, 30, 39, 40)
• Transport of neurotransmitters across membrane (SLC6)
• Transport of neurotransmitters in storage vesicles (SLC18)
• Transport of drugs eg. SLCO for statins and antidiabetics
• SLC 22 for anionic and cation drug transport

16. Associated diseases with SLC
GENE FAMILY DISEASE
ASSOCIATED
SLC 4 Bicarbonate transport Distal renal tubular
acidosis
SLC 12 Sodium – chloride
cotransport
Gitelman syndrome
SLC 19 Folate /Thiamine
transport
Thiamine responsive
megaloblastic anemia

17. SLC mechanism

18. Transporters as drug targets
• Serotonin transporter (SERT): SSRI’S (Depression)
• Vesicular monoamine transporter (VMAT) inhibitor: Tetrabenazine
(Huntigton’s Chorea)
• Sodium glucose transporter (SGLT2) inhibitor: Canaglifozin,
dapaglifozin (Type 2 Diabetes)
• Uric acid transporter1 (URAT1) Inhibitor: Lesinurad (Gout)
• CFTR potentiator: Ivacaftor (cystic fibrosis)

19. Transporters in drug resistance
• Increased efflux: antitumor resistance
• Decreased uptake: folate antagonist, nucleoside analogue, platinum
complex
• Overexpression of multidrug resistance protein (MRP4): antiviral
resistance
• Overexpression of p glycoprotein (Pgp/ ABCB1) and Breast cancer
resistance protein (BCRP /ABCG2): Anticancer resistance

20. Membrane transporter and ADR
Three Reasons described for ADR via Membrane Transporters

21. Membrane transporter and ADR
1. Decreased uptake or excretion from excretory organs

22. 2. Increased uptake or decreased efflux at target organ
Membrane transporter and ADR

23. 3. Altered transport of endogenous compound at target organ
Membrane transporter and ADR

24. Transport mediated ADRs
1. Loperamide
Not accumulated in brain because of Pgp mediated efflux in BBB
Avoid loperamide with quinidine (Pgp inhibitor)
Leads to respiratory depression
2. Metformin
Exported via MATE1(Multidrug and toxin extrusion protein1 )
Inhibition of MATE1 by tyrosine kinase inhibitor leads to toxicity of
metformin
Uptake in liver by OCT1
Inhibition of OCT1 may lead to less lactic acidosis

25. Transporters in pharmacokinetics
HEPATIC TRANSPORTERS
SLC transporter for uptake of drugs & bile salt on basolateral membrane
• OAT (organic anion transporter)
• OCT (organic cation transporter)
• NTCP (Na taurocholate co-transporting polypeptide)
ABC transporter for efflux of drugs, bile salts and phospholipids on bile
canalicular membrane
• MRP2 (multidrug resistance protein 2)
• BSEP (bile salt export pump)
• BCRP (breast cancer resistance protein)

27. EXAMPLES
• HMGCoA Reductase inhibitor uptake by OATP1B1
• Irinotecan
BY MRP2
Probenecid

28. Renal transporters
Organic cation transporter: for elimination
Endogenous compound like choline and dopamine
Drugs like metformin, ranitidine (positively charged drugs)
• On basolateral membrane: SLC 22 family transporter OCT2
(SLC22A2) and OCT3 (SLC22A3)
• On luminal membrane: MATE1(multidrug and toxin extrusion
protein)(SLC47A1) and MATE2 (SLC47A3), OCTN1 (SLC22A4)
and OCTN2 (SLC22A5)

30. Organic anion transporter: for removal of xenobiotics
• On basolateral membrane:
OAT1 (SLC22A6)
OAT3 (SLC22A8): secondary active transport and depends on alpha
ketoglutrate
• On apical membrane:
OAT4 ( secondary active transport)
MRP2 and MRP4(multidrug resistance protein) (ABCC family)
URAT1 (uric acid transporter 1) for urate reabsorption
Renal transporters

32. Transporter in brain
• Involved in reuptake of NT and regulation in synaptic cleft
• Two major superfamilies SLC1 & SLC6
GABA uptake: GAT1 GAT2 GAT3
• Target for antiepileptic: Tiagabine
NET (Norepinephrine transporter)
• Target for TCA and cocaine
 DAT (Dopamine transporter)
• Target for cocaine and amphetamine
 SERT (Serotonin transporter)
• Target for SSRI eg. Fluoxetine, paroxetine