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