Na+ 117A- 0K+ 3Cl- 120

Model cell

Extracellular Intracellular

30116904

Nernst equation

K+ equilibrium potential: no net K+ movement

In reality: limited Na+ permeability

i

o

K

Kln *

zF

RT KE

-

-

+

+

K+, Cl- permeable Na+, A- non permeable

+

+

ATP

ADP

ATPADP

[Ca2+]i

K+

[Na+]i 10 mM

[Na+]o140 mM3 : 2 electrogenic

Na,K-ATPase

Ca2+-ATPase [Ca2+]i 2 mM

100 nM

[K+]i 140 mM

[K+]o

5 mM

- 90 mV

Li+ can replace Na+

from the cytoplasmic sidebut

with lower efficiency

Nernst equation

V

iK

oK

lnzF

RTk

E

mV

oK

iK

log*58kE

i-

oo

o-

ii

ClPNaPKP

ClPNaPKP58xlogEm

-ClNaK

-ClNaK

Goldman – Hodgkin – Katz equation

E1 conformation•High affinity for Na and ATP

E2 conformation •low affinity for ATP

Extracellular side

Cytoplasmic side

Ionophor domain: 3,4,5,(8?) transmembrane segment

369 - aspartate

-alegység -55 k Da - 4 isoform - necessery for activation - S–S links -glycosylated

100 kDa 4 izoforma

P-type ATP-ases

Na, K-ATPaseα1

α2

α3

α4

K, H-ATPase (K+-absorption; H+- excretion) stomach parietal cells

SERCA ATPaseSERCA 1 striatal muscleSERCA 2 smooth muscle, striatal muscle, heart muscle -

phospholambaneSERCA 3 platelets, endothelial cells

Plazma membrane Ca2+- ATPasePMCA 1 generalPMCA 2 neuronal - higher affinity for cAMP phosphorylation

than PMCA 4 PMCA 3 striatal muscle, brainPMCA 4 generalPMCA 5

ATP dependent aminophospholipid translocase phosphatidyl serine, phosphatidyl etanolamine asymmetric membrane distribution

P-type ATP-ases

Extracellular.

Citoplasmic

Na+

K+

ATP

ATP

22 tetramer (270 kD)

Optimal phospholipid environment- fluidity

Ouabain

Ca2+

Ca2+

Na+

ATP-ase isoforms:

at least 5 different genes -different sensitivity to ouabain in different tissues

α subunit isoforms

α1 - most cells, in epithelial cells only this oneα2 - striatal muscle, brain, heartα3 - neurons, heartα4 - testis

Sensitivity to ouabain:

Kd α2 > α3 > α1

0.1 pM 30 nM 0.1 mM

Piros gyűszűvirág(Digitalis purpurea)

~ 30% of the total ATP production

In neurons ~ 50 % (Na, K-ATPase: voltage-dependent Na+ channels

= 10 :1)

At normal [Na+]i and [K+]o activity is 10-15% of the maximal large reverse capacity

In neurons the activity is increased by 2.5 – 25 folds during action potentials

K0.5 for ATP is 300 - 800 µMAnoxia!

α subunit isoformes

α1 - in most cells, in epithelial cells exclusivelyα2 - striated muscle, brain, heartα3 - neurons, heartα4 - testis

Different sensitivity to cardiac glycosides:

Kd α2 > α3 > α1

0.1 pM 30 nM 0.1 mM

Effects of digitalis-like compounds (DLC)

Regulation

γ – subunit (1978)

szövet-specifikus Na, K-ATPáz regulátor (vese, pancreas, fötális máj)7.2 KDa (58 aminosav) - egy transzmembrán domain Nem integráns része az enzimnekNöveli az enzim ATP iránti affinitásátSzerepe van a K+ általi aktiválásban

Jelentősége:anoxiábanFiziológiásan a vese velőállomány közel anoxiás körülmények között működikReabszorpciók a Na-pumpa kontrollja alatt állnakKis mértékű ATP affinitás növekedés → pumpa aktivitás ↑(Fine tuning! Nagy mértékű affinitas növekedés további ATP ↓ okozna!)

To the proper function of the pump: Na+

i and K+o is required

[K+]o saturates the binding place

[Na+]i < than required to 50 % saturation

The pump responds to changes in [Na+]i

ESSENTIAL HYPERTENSION(SODIUM - VOLUME dependent – low renin level)

Kidney Na+ excretion ↓ ↓[Na+] plasma ↑ ↓Circulating blood volume ↑

? ↓ ? Ouabain release – adrenal cortex ↓ Vascular tone ↑ [Na+]i ↑ → Na - Ca exchange → [Ca2+]i ↑ Long treatment with cardiac glycosides → → hipertension

HORMONES

Corticosteroids (aldosterone, dexamethazon)aldosterone: long term adaptation to decreased Na+ intake

kidneylong term effect – increased expression of mRNA of Na,K-ATPaseshort term effect – increased activity of enzymee (decrease of KM to Na+?)

long term upregulation – described for α1, α2, α3 (smooth

muscle, brain, heart)

ENDOGENOUS STROFANTIN

Regulation

Na,K-ATPase in specialized cells

Kidney:Na reabsorbtion

Na/Ca exchangedigitalis

After stimulation ofstretch aktivatedchannelsremoval of Na

neuronglia

ADRENALIN

Tissuespecific effectActivation of Na,K-ATPase in striated musclesdecreases hyperkalemic detected after muscle work

Secondary active transports

Na cotransporters

*Glucose absorbtion*Amino acid absorbtion*Ca2+ (Na+-Ca2+exchanege)*Cholin uptake into the cholinergic nerve terminal*Adrenalin, noradrenalin. dopamin, serotonin uptake into the axon terminal*Na+-H+ exchange

Inhibition by spec inhibitors + ouabain

Na-H exchanger (NHE)

i

o

H

Hln

zF

RT77

[H+]i = 730 nM pH = 6.13

Na+

H+

1:1 non electrogenic

pHi 7,0883 nM

pHo 7,3844 nM

-77 mV

5 izoforma12 transzmembrán régióNHE 1 általános (basolateralis membrán)

regulált, neurotranszmitterekhormonoknövekedési faktoroksejt térfogat csökkenés

H+ affinitás ↑→ citoplazma alkalinizálás

NHE 3 epitel sejtek apikalis membránjában

NHE 5 agy, lép, testis

KidneyNa+ reabszorpció

Proximal tubules(Na+-H+ exchanege)

Collecting tubules(Na+ channel)

Ca = szensav anhidraz

Neurotransmitter

H+

Citoplazma

ATP

ADP

H+

~ pH = 6