3.3: Uniporters

summary

tranporters act in concert

  • influx: net uptake

  • efflux: extrusion from


achieved by a combination of

  • primary active transport (pumps)

  • secondary active transport (symporters and antiporters)

  • passive transport (uniporters and channels)


uniporters (passive transporter)

  • understand the functional characteristics of uniporters

  • uni = one thing

    • moving one thing at a time

GLUT family of transporters

Glucose transporter

  • ping pong mechanism

  • passive transporter

  • protein binds → conformational change

    • outward facing → inward facing → outward facing

  • there are 14 members found in humans

  • plasy many roles

radiolabelled experiment

  • pre-load cell with radiolabelled gluose

  • measure the rate of radiolabelled glucose leave the cell


why doe unlabelled gluc outside the cell speed up the efflux of labelled glucose from inside the cell

  • unlabelled gluc from outside cell speeds up efflux of radiolabelled gluc inside cell

  • trans-stimulation

trans-stimulation mechanism

  • rate flattens out

    • rate limiting step

GLUTs

GLUT1

  • blood-brain barrier

  • GLUT1 in cancer cells

    • most cancer cells use glycolysis (fueled by glucose) as their main ATP production method instead of mitochondrial oxidative phosphorylation

    • overexpressed in many types of cancer, including the brain

    • blocking GLUT1 starrves cancer cells but also starves the brain


GLUT2

  • kidney cells and intestinal cells

  • in liver and pancreatic beta cells as well


GLUT3

  • neurons in placenta


GLUT4

  • expressed in adipose tissue and striated muscle (skeletal muscle and cardiac muscle)

  • regulated by insulin