Membrane transport Energy driven pumps Chemiosmotic coupled transporters Solute control.
-
Upload
donna-anabel-cummings -
Category
Documents
-
view
213 -
download
0
Transcript of Membrane transport Energy driven pumps Chemiosmotic coupled transporters Solute control.
Membrane transport
• Energy driven pumps
• Chemiosmotic coupled transporters
• Solute control
ATP driven pumps
• P-type ATPase– Cation exchangers
• Ca2+/H+• Na+K+• H+/K+
• F0F1
– H+– ATP synthesis
• Energy efficient = reversible• ABC transporters
– Nonionic species – peptides, drugs– CFTR – Cl-
P-type, E1-E2 Pump
• ATP-driven calcium pump
• SERCA, NaK, HK, heavy metals– Ca2+, Na+, H+ out of cytoplasm
• Staged ATP releaseE1 E1-ATP-2Ca E1P-ADP-2Ca
E2P-2CaE2PE2
SERCA structureE1 E2
F0F1 pump
• Rotary protein complex
• V1-ATPase– H+ out of cytoplasm– Mostly into vesicles
• F1-ATP synthase– Mitochondria
ATP
ADP
Proton Gradient
H+
H+
ATP
ADP
H+
H+
High energy H+
Low energy H+
ABC Transporters
• esp. prokaryotes
• Heterotetramer
• 2 ATP per cycle
• Peptide uptake
• Toxin emission
Locher et al., 2002
Transporter regulation
• Phosphorylation– InsulinPKC/srcNaK activity
• Ions– Mg2+, Mo2+..
• Accessory proteins– NoradrenalinePKA--|phospholamban--|SERCA
• Substrate concentrations– Mass action
Non-ATP powered transporters
• Energy sources– Own concentration gradient (uniporter)– Other gradient
• Symporter• Antiporter
– Chemical modification• Released molecule different than adsorbed
Maj
or
faci
litat
or
Gro
up
T
ran
spo
rt
Uniporter
• Glucose transporter GLUT1/GLUT4
• Not a pore
• Ligand mediated conformational change
• Bi-directional, slow vs true channel
Lachall et al., 1996
Glucose uptake in high-glucose Glucose release in low glucose
Inhibited by actin filament disruption
Antiporter
• NHE Na+/H+ exchanger– High Na+ gradient (15 kJ/mole)– Proton efflux, pH control
• Bistable proteins– Opposing openings– Substrates stabilize
one or the other facing– Transition energy > thermal
Symporter
• Na+/K+/2Cl- cotransporter– Electroneutral
• Independent of equilibrium potentials• Solely concentration gradients
– Major source of Cl- entry– Electrolyte & osmotic balance
• Substrate binding stabilizestransitional conformation
MFS regulation
• Membrane transport/sequestration
• Phosphorylation
Blood homeostasis
• Volume/pressue homeostasis
• Composition homeostasis
• Kidney function– Osmotic regulation– Hormonal regulation– Neural regulation
Mass flow in kidney
• NaK (P-type)• Kleak, Cl (ion channel)• NHE (MFS antiporter)• NKCC, NGC, ATA (MFS symporter)• GLUT, AA (MFS uniporter)
Lumen Tissue interstium
NKCC
NHE
NGC
ATA
Na
K
Cl
Glucose
AA
Pi
H
NaK
GLUT
AA
CBA
OH
CO2
HCO3
Na
K
Glucose
AA
Cl
Kleak
Ca
Ion currents in kidney
• Asymmetric distribution of transporters– Diffusion on one side– Counter-diffusive movement opposite
• ATPNa gradientglucose gradient
Lumen Tissue interstium
NHE
Na
K
Cl
Glucose
AA
Na
Glucose
AA
Kleak
NGC
ATA
GLUT
AA
NKCC NAK
ATP Energy
Na EnergyAA Energy
Glucose Energy
Regulatory specifics
• Phosphorylation– Cell shrinkage cAMPPKANKCC activity– Vasopressin AVPR2GsNaK activation– AngiotensinAT2--|cAMPPKA--|NHE
• Transport– EGF PI3KNHE3 internalization– Lumen pressureNHE internalization– AT2PLCCaMKIINHE externalization
• Genetic– Aldosterone NaK upregulation