Pumps

Outline by Shelby Pickett and Avalon Marker

Pumps

• Na+/K+ pump
  • The sodium-potassium pump is found in many cell (plasma) membranes. Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient. In a single cycle of the pump, three sodium ions are extruded from and two potassium ions are imported into the cell.
  • Sodium/Potassium pump helps maintain resting potential, affects transport and regulates cellular volume.
  • For a cell to have a resting membrane potential, charge separation across membranes must be constant over time.
  • If fluxes are not equal, the charge separation across the membrane varies continually.
  • The passive movement of potassium out of the resting cell through open channels balances the passive movement of sodium into the cell.
  • The pump needs energy, energy comes from the hydrolysis of ATP
  • During periods of intense neuronal activity, the increased influx of sodium leads to an increase in sodium/potassium pump activity that generates prolonged outward current, leading to prolonged hyperpolarizing.
  • Hyperpolarization is a change in a cell’s potential that makes it more negative.
  • The export of sodium ions from the cell provides the driving force for several secondary active transporters such as membrane transport proteins, which import glucose, amino acids, and other nutrients into the cell by use of the sodium ion gradient.
  • Another important task of the Na+-K+ pump is to provide a Na+ gradient that is used by certain carrier processes. In the gut, for example, sodium is transported out of the reabsorbing cell on the blood (interstitial fluid) side via the Na+-K+ pump, whereas, on the reabsorbing (lumenal) side, the Na+-glucose symporter uses the created Na+ gradient as a source of energy to import both Na+ and glucose, which is far more efficient than simple diffusion.
  • Opening of chloride channels will bias the membrane potential toward its Nernst potential.
  • Chloride membranes typically use the energy stored in the gradients of other ions – which means they are cotransporters.
  • In some pathological conditions in adults such as epilepsy or chronic pain syndrome, the expression pattern of the chloride cotransporters may revert to that of an immature nervous system – this will lead to aberrant depolarizing responses to GABA.
• H+ pump