ion pump

(noun)

Critical membrane proteins that carry out active transport by using cellular energy (ATP) to "pump" the ions against their concentration gradient.

Related Terms

Examples of ion pump in the following topics:

  • Ion Channels

    • Ion channels are membrane proteins that allow ions to travel into or out of a cell.
    • Most channels are specific (selective) for one ion.
    • Ion pumps are not ion channels, but are critical membrane proteins that carry out active transport by using cellular energy (ATP) to "pump" the ions against their concentration gradient.
    • Such ion pumps take in ions from one side of the membrane (decreasing its concentration there) and release them on the other side (increasing its concentration there).
    • A schematic representation of an ion channel.

  • Body Fluid Composition

    • The cell membrane separates cytosol from extracellular fluid, but can pass through the membrane via specialized channels and pumps during passive and active transport.
    • In contrast to extracellular fluid, cytosol has a high concentration of potassium ions and a low concentration of sodium ions.
    • The reason for these specific sodium and potassium ion concentrations are Na+/K ATPase pumps, which facilitate the active transport of these ions.
    • These pumps transport ions against their concentration gradients to maintain cytosol fluid composition of ions.
    • Some of the electrolytes present in the transcellular fluid are sodium ions, chloride ions and bicarbonate ions.

  • Membrane Potentials as Signals

    • The membrane serves as both an insulator and a diffusion barrier to the movement of ions.
    • Ion transporter/pump proteins actively push ions across the membrane to establish concentration gradients across the membrane, and ion channels allow ions to move across the membrane down those concentration gradients, a process known as facilitated diffusion.
    • The opening and closing of ion channels can induce a departure from the resting potential.
    • The changes in membrane potential can be small or larger (graded potentials) depending on how many ion channels are activated and what type they are.
    • Action potentials are generated by the activation of certain voltage-gated ion channels.

  • Rigor Mortis

    • ATP is no longer provided to operate the SERCA pumps in the membrane of the sarcoplasmic reticulum; these pumps move calcium ions into the terminal cisternae.
    • This release of calcium is caused by the loss of ATP-mediated function of calcium pumps of the sarcoplasmic reticulum, due to ATP depletion in the absence of cellular respiration.
    • Diffusion of the calcium through the pumps occurs, facilitation binding of myosin and actin filaments.

  • Short-Term Chemical Control

    • The mechanism that leads to vasoconstriction results from the increased concentration of calcium (Ca2+ ions) and phosphorylated myosin within vascular smooth muscle cells.
    • Once elevated, the intracellular calcium concentration is returned to its basal level through a variety of protein pumps and calcium exchanges located on the plasma membrane and sarcoplasmic reticulum.
    • As with vasoconstriction, vasodilation is modulated by calcium ion concentration and myosin phosphorylation within vascular smooth muscle cells.
    • Dephosphorylation by myosin light-chain phosphatase and induction of calcium symporters and antiporters that pump calcium ions out of the intracellular compartment both contribute to smooth muscle cell relaxation and therefore vasodilation.
    • This is accomplished through reuptake of ions into the sarcoplasmic reticulum via exchangers and expulsion across the plasma membrane.

  • Tubular Reabsorption

    • Active Transport-membrane bound ATPase pumps (such as NA+/K+ ATPase pumps) with carrier proteins carry substances across the plasma membranes of the kidney epithelial cells by consuming ATP.
    • Water can follow other molecules that are actively transported, particularly glucose and sodium ions in the nephron.
    • As filtrate passes through the nephron, its osmolarity (ion concentration) changes as ions and water are reabsorbed.
    • The filtrate osmolarity drops to 1200 mOsm/L as water leaves through the descending loop of henle, which is impermeable to ions.
    • In the ascending loop of henle, which is permeable to ions, but not water, osmolarity falls to 100-200 mOsm/L. finally in the distal convoluted tubule and collecting duct, a variable amount of ions and water are reabsorbed depending on hormonal stimulus.

  • Myocardial Thickness and Function

    • The thickness of the myocardium determines the strength of the heart's ability to pump blood.
    • At these T-tubules, the sarcolemma is studded with a large number of calcium channels which allow calcium ion exchange at a rate much faster than that of the neuromuscular junction in skeletal muscle.
    • The flux of calcium ions into the muscle cells causes stimulates an action potential, which causes the cells to contract.
    • Eventually, hypertrophy may become so severe that heart failure occurs when the heart becomes so stiff that it can no longer pump blood.
    • If the heart adapts to become too thick, it will not be able to pump blood as efficiently, and heart failure may occur.

  • Tubular Secretion

    • Active transport-movement of molecules via ATPase pumps, that transport the substance through the renal epithelial cell into the lumen of the nephron.
    • The substances that are secreted into the tubular fluid for removal from the body include: potassium ions (K+), hydrogen ions (H+), ammonium ions (NH4+), creatinine, urea, some hormones, and some drugs (e.g., penicillin). 
    • The movement of these ions also helps to conserve sodium bicarbonate (NaHCO3).
    • At this final stage it is only approximately one percent of the originally filtered volume, consisting mostly of water with highly diluted amounts of urea, creatinine, and variable concentrations of ions.

  • Regulation of Urine Concentration and Volume

    • ADH is a hormone secreted from the posterior pituitary gland in response to increased plasma osmolarity (ie. increased ion concentration in the blood), which is generally due to increased concentration of ions relative to volume of plasma, or decreased plasma volume.
    • This effect causes increased water reabsorption and retention, decreasing the volume of urine produced relative to its ion content.
    • Many medications are diuretics by inhibiting the ATPase pumps, thus inhibiting water reabsorption further.
    • As the fluid flows along the proximal convoluted tubule useful substances like glucose, water, salts, potassium ions, calcium ions, and amino acids are reabsorbed into the blood capillaries that form a network around the tubules.

  • Overview of Urine Formation

    • Normally, about 20% of the total blood pumped by the heart each minute will enter the kidneys to undergo filtration; this is called the filtration fraction.
    • The next step is reabsorption, during which molecules and ions will be reabsorbed back into the circulatory system.
    • The fluid passes through the components of the nephron (the proximal/distal convoluted tubules, loop of henle, collecting duct) during which water and ions are removed as fluid osmolarity (ion concentration) changes.
    • During secretion, some substances such as hydrogen ions, creatinine, and drugs will be removed from blood through the peritubular capillary network into the collecting duct.