Transport of Sodium and Chloride 1 and 2 Flashcards
How much of the sodium and chloride of the glomerular filtrate is reabsorbed in the proximal tubule?
55-65%
types of active transport in the neprhon
ATP-dependent
Co- and counter-transport
types of passive transport in the nephron
facillitated diffusion
channel-mediated diffusion
NA+/K+ ATPase
uses ATP to transport 3 Na+ out and 2 K+ into the cell
always located in the basolateral membrane
allows sodium to be the major energy currency of tubule cell transport
co- and counter-transport
transporters that couple favorable movement of sodium and/or potassium to move other ions and solutes
transcellular transport
solutes are taken up at the apical surface of the cell and traverse the cytoplasm and are excreted at the basolateral surface into the bloodstream
paracellular transport
ions/solutes flow between tubule cells
the driving force for paracellular flux comes from the lumenal vs. basolateral electrochemical gradient
extent depends on number and orcanization of tight junctions
What is the advantafe of a large paracellular flux?
mitigates against the formation of large electrical and chemical gradients
solvent drag
the process where bulk flow can carry ions and solutes against their graidents
occurs during massive water flux, particularly in the proximal tubule
paracellin-1
an Mg2+ channel located between cells of the thick asending limb and distal tubule
What are the reference points for membrane potentials?
outside the cell for transmembrane
interstitial for across lumen and interstitium
membrane potential in the presence of leaky tight junctions
the tubule cell behaves like an isolated cell
the voltage across each piece of membrane, apical or basal, is the same
transepithelial voltage = 0 mV
membrane potential in the presence of tight tight junctions
ionic conductances in the apical and basal membranes sum separately
basal K+ channels set voltage to -70 mV and apical Na+ channels set transmembrane voltage to +70 mV
transepithelial voltage = -140 mV
solute selectivity of the paracellular pathway
based on size
the cut-off can be in the 100s of mw
ion selectivity of the paracellular pathway
based on charge
resistance of the paracellular pathway
varies with the number of rows of junction proteins
increases along the tubule
What is the NaCl concentration in glomerular filtrate?
142 mM NaCl
What is the concentration of NaCl that the kidney excretes?
120 mM
What is the consequence of having leaky paracellular contacts in the proximal tubule?
the uptake becomes iso-osmotic
the solution that leaves the tubule has a similar ionic concentration to that entering the tubule
as a result, there is much less solution leaving and thus less total NaCl
proximal tubule sodium transcellular re-uptake mechanisms
apical cotransporters for glucose, amino acids, and other metabolites
apical Na+/H+ antiporter
basaolateral Na+/K+ ATPase
basolateral Na+/HCO3- transporter
proximal tubule sodium paracellular re-uptake mechanisms
osmotic gradient created by Na+ and HCO3= draws water from the lumen, carrying Na+ via solvent drag
proximal tubule transcellular Cl- re-uptake mechanisms
little or none in the first part of the proximal tubule, where Cl- in the lumen is increased from 115 to 135 mM
in the late proximal tubule, Cl- is unfavorably taken up at the apical surface through an electroneutral Cl-/anion counter-transporter
basolateral transport passively via an ion channel
basolateral transport coupled to a favorable K+ efflux
What are the possible anions in the late proximal tubule for chloride cotransport?
formate, OH-, HCO3-, and oxalate
proximal tubule paracellular Cl- re-uptake mechanisms
small amount occurs in the early proximal tubule via solvent drage promoted by the -3mV gradient across the tubule cell tight junctions
significant uptake in the late proximal tubule favored by an increased lumen to blood Cl- gradient