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
