6.11-6.18 Flashcards
function of aquaporins
- thirst mechanism
- concentration of urine by kidneys
- regulation of body temperature
- secretion/absorption of spinal fluid
- secretion of tears, saliva, sweat, and bile
- reproduction
aquaporins are homo_________
tetramers
each subunit of an aquaporin forms what?
its own separate pore
features of water specificity of aquaporins
- size restriction via constriction region
- electrostatic repulsion via positive charges lining pore
- water dipole orientation
what do aquaporin-1 type of protein channels help to concentrate
180 of blood filtrate per day into a urine volume of 1.5 liters per day by reabsorbing water
where does aquaporin-1 have high water permeability
in epithelial cells of proximal convoluted tubules and descending thin limbs of the loop of Henle
what does vasopressin stimulate the expression of
aquaporin-2 in the collecting ducts, resulting in increased urine concentration
steps of action potential
- opening of voltage-gated Na+ channels, rapid flow of Na+ ions into the cell causes membrane depolarization
- Na+ channels rapidly inactivate - repolarization beings, voltage-gated Ca2+ channels open
- transient outward K+ currents balance Ca2+ channels
- more K+ ions rapidly exit the cell - repolarization
- Na+/K+ATPase at work this whole time
how are cardiac and skeletal muscles activated
by excitation-contraction coupling
excitation-contraction coupling
process in which membrane depolarization results in production of force by muscles (cardiac and skeletal)
steps of excitation-contraction coupling
- signal initiated at plasma membrane when depolarized from incoming signal - voltage-dep Ca2+ channels sense this change and open, allowing small flux of Ca2+ ions to enter the cell
- stimulates release of lots of Ca2+ from SR through RyRs
- increase in cytosolic Ca2+ activates Ca2+ sensitive protein troponin C, which stimulates contraction of the myofilaments
- extrusion of Ca2+ from the cytosol causes muscle to relax
what are RyRs
ryanodine receptors - intracellular Ca2+-gated Ca2+ release channels
2 methods of extrusion of Ca2+ ions
- reuptake of Ca2+ into SR by the SR Ca2+-ATPase pump
- removal of Ca2+ ions from the cytosol by the Na+/Ca2+ exchanger in the pm
another type of intracellular Ca2+ release channel
IP3R (inositol 1,4,5-triphosphate receptor) - gated by IP3
2 distinct gene families of glucose transporter proteins in the plasma membrane
- GLUTS
- Na+/glucose cotransporters
GLUTS
glucose transporters that are uniporters which mediate facilitated transport of glucose down its concentration gradient
Na+/glucose cotransporters
couple energy of the transmembrane Na+ gradient to the transport of glucose
GLUTS are part of ____
MFS
MFS
major facilitator superfamily - largest superfamily of proteins involved in membrane transport, ubiquitous in all living organisms
what can GLUTS carry
glucose, galactose, water, painkillers
what is GLUT-1 important for
facilitating glucose into the brain by transporting glucose from blood into endothelial cells (BBB) to ECM to astrocyte
what is GLUT-4 responsive too
insulin
what is GLUT-4 important for
mediates glucose uptake by muscle and adipose tissue
- located in intracellular vesicles that upon receipt of signal (insulin) fuse with plasma membrane to increase glucose transport
cause of type II diabetes
not enough GLUT-4 in the pm
2 major conformations of GLUT proteins
- glucose binding site faces extracellular space
- glucose binding site faces intracellular space
- binding of glucose on either side would induce a conformational change to opposite side of membrane to release
symporters and anti porters move one solute _______ its transmembrane concentration gradient by using second solute ______ its transmembrane gradient
against, down
many transporters are part of what?
MFS
LacY
bacterial lactose permeate, monomeric oligosaccharide/H+ symporter
how does LacY work
uses H+ gradient (toward cytosol) to drive accumulation of nutrients such as lactose against its concentration gradient
what is H+ gradient in bacterial cells generated by
combination of ETS and F1F0 ATPase which can couple ATP hydrolysis to export of protons from the cytosol
can the LacY work in one or both directions
both
- can use lactose gradient to generate an H+ gradient
Na+/substrate transporters are involved in transporting what?
ions, sugars, amino acids, vitamins, urea
different types of Na+ cotransporters
Na+/glucose symporter
Na+/iodide cotransporter
Na+/proline cotransporter
Na+/glucose cotransporter
- Na+ binds, followed by conformational chagne
- sugar binds, another conformational change exposes Na+/glucose to intracellular side of the membrane
- released into cytosol, causing another conformational change and resetting to starting position
Na+/Ca2+ exchanger
transports 3 Na+ ions in exchange for 1 Ca2+ ion
- net electrogenic current of 1+ per cycle
primary Ca2+ extrusion system to the ECM side of the pm
Na+/Ca2+ exchanger
Na+/K+/Cl- cotransporter
mediates electroneutral transport with stoichiometry of 1:1:2, cotransported into cells
why is the Na+/K+/Cl- cotransporter important
- maintains intracellular Cl- concentration
- reabsorption of NaCl from kidney filtrate
Na+/Mg2+ exchanger
transports 2 Na+ ions in for each Mg2+ extruded (neutral)
why is the Na+/Mg2+ exchanger important
need to get ride of excess Mg2+ that constantly permeates into the cytosol at a low rate
which Na+ transporters regulate pH?
Na+/H+ exchanger and Na+/HCO3- cotransporter
what enzyme is involved with Na+ regulation of pH
carbonic anhydrase
how do the lungs and the kidneys maintain the acid-base balance of the plasma
by excreting CO2 out of lungs and H+ into urine
what is the secretion of H+ into the lumen filtrate (urine) by the apical membrane Na+/H+ exchanger coupled to?
the transport of an equal number of bicarbonate ions into the blood via the Na+/HCO3- cotransporter in the basolateral membrane of epithelial cells of the proximal tubule
what does the ER function as
intracellular Ca2+ storage compartment
after Ca2+ signaling has occurred, resting Ca2+ concentrations are ____________
reestablished
SERCA pump reaction cycle
phosphorylation and dephosphorylations, power uphill transport of 2Ca2+ ions into SR per hydrolyzed ATP in exchange for 2H+ ions
PMCA
similar to SERCA, 1 Ca2+ per ATP hydrolyzed
- aren’t as many
SERCA/PMCA are both what kind of pumps?
P-type pumps
P-type pumps
dependent on ATP and use it to autophosphorylate a conversed aspartic acid residue
GLUT1
- blood, blood-brain barrier, heart
- insulin-independent
GLUT2
- liver, pancreas, small intestine
- insulin-independent
- high Km
- low affinity
GLUT3
- brain, neurons, sperm
- insulin-independent
- low Km
- high affinity
GLUT4
- skeletal muscle, adipose tissue, heart
- insulin-responsive
