Chapter 13. Membrane Channels and Pumps Flashcards
a phenomenon observed in cancer cells in which the development of resistance to one drug renders the cells resistance to a range of other drugs. The resistance is due to the action of an ATP-dependent pump called the multidrug resistance protein (MDR), which contains an ABC domain.
Multidrug resistance
ATP-dependent pump, containing an ABC domain, that pumps drugs out of a cell.
Multidrug-resistance (MDR) protein (P–glycoprotein)
Compounds derived from cholesterol that inhibit the Na+-K+ pump by blocking the dephosphorylation of the E2 conformation of the pump protein. Inhibition of the pump in cardiactissue cells leads to a higher level of sodium ion in the cells, which slows the extrusion of calcium ion and enhances cardiac muscle contractility.
Cardiotonic steroid
family of enzymes that uses the energy of hydrolysis to move ions across membranes. They are called P-type ATPases because the reaction mechanism includes a phosphoaspartate intermediate.
P-type ATPase
The interconverting of a site on a membrane protein from one of exposure to the extracellular environment to one of exposure to the intracellular environment.
Eversion
the ATP-binding domain characteristic of specific membrane transport proteins, called ABC transporters. These transporters also contain a membrane spanning region.
ATP-binding cassette (ABC) domain
Membrane proteins that use the energy of ATP hydrolysis to drive the thermodynamically uphill transport of ions or molecules.
ATP-driven pump
Protein channels that transport water across membranes.
aquaporin
A membrane protein that is responsible for pumping sufficient protons into the stomach, at the expense of ATP hydrolysis, to lower the pH to 1.0.
Gastric H+–K+ ATPase
The increase in membrane potential and the changes in sodium and potassium conductances that result from alterations in the permeability of the axon membrane to those ions. Also called nerve impulse.
Action potential
A ligand-gated channel that promotes a large inward current of sodium ions and triggers an action potential; composed of a pentamer of four kinds of polypeptide subunits, the channel opens to allow passage of sodium and potassium ions when two acetylcholine molecules promote transient opening of the channel.
Acetylcholine receptor
Membrane proteins that mediate the transport of ions and small molecules across the membrane without consumption of ATP.
Carrier
transport of an ion or a molecule against a concentration gradient, where delta G for the transported species is positive, and where the process must be coupled to input of free energy from a source such as ATP, an electrochemical gradient of Na+ or K+, or light.
Active transport
a transport system in which a molecule is carried across the membrane in the same direction as an ion, which in turn is pumped back across the membrane through active transport linked to ATP consumption.
Antitransporter (symporter)
a mixture of cardiotonic steroids derived from the dried leaf of the foxglove plant. Such steroids inhibit the sodium-potassium pump.
Digitalis
Membrane proteins that catalyze active transport and contain ATP binding (ABC) cassettes.
ABC transporter
A common neurotransmitter that exerts its effects by first binding to the acetylcholine receptor.
Acetylcholine
These proteins couple the downhill (exergonic) flow of one species to the uphill (endergonic) flow of another in the opposite direction across the membrane.
antiporter
A symporter that uses the H+ gradient across the E. coli membrane (outside has higher H+ concentration) generated by the oxidation of fuel molecules to drive the uptake of lactose and other sugars against a concentration gradient.
Lactose permease
A model for the regulation of the K+ channel that postulates that the first 20 residues of the K+ channel form a cytoplasmic unit (the ball) that is attached to a flexible segment of the polypeptide (the chain). When the channel is closed, the ball rotates freely in the aqueous solution. When the channel opens, the ball quickly finds a complementary site in the open pore and occludes it.
Ball-and-chain model
passive transport systems for ions capable of very high transport rates. Ion channels often display a high degree of specificity for the transported ion.
Ion channel
A membrane protein that transports Ca2+ out of the cytoplasm and into the sarcoplasmic reticulum of muscle cells at the expense of ATP hydrolysis.
Sarcoplasmic reticulum Ca2+ ATPase (SERCA)
The movement of lipophilic molecules through a membrane down their concentration gradient.
Simple diffusion
A process in which the free energy of ATP hydrolysis is used to drive the movement of ions against their concentration gradients.
Primary active transport
a transporter that uses the energy of the downhill (exergonic) flow of one ion or molecule to power the uphill (endergonic) flow of another.
Secondary transporter (cotransporter)
Membrane proteins that provide a pore through which ions can flow very rapidly in a thermodynamically downhill direction.
Channel
Transport of an ion or a molecule down a concentration gradient, where .G for the transported species is negative. Also called passive transport.
Facilitated diffusion (passive transport)
a method for studying ion channels in which a high-resistance seal is formed between a pipette and a small patch of plasma membrane, allowing the monitoring of the flow of ions through a single channel with high time resolution.
Patch-clamp technique
Six connexin molecules hexagonally arrayed to form a half-channel. Two connexons form a functional gap junction.
Connexon (hemichannel)
A thermodynamic measure of the energy resulting from an unequal distribution of a population of molecules across a membrane that takes in account concentration differences and charge differences between the two sides of the membrane.
Electrochemical potential (membrane potential)
The equilibrium achieved when the driving force due to a concentration gradient is balanced by an electrostatic force resisting the motion of additional charges; applies to a membrane separating two different concentrations of ion with a channel connecting the two sides of the membrane.
Equilibrium potential
The increase in membrane potential and the changes in sodium and potassium conductances that result from alterations in the permeability of the axon membrane to those ions. Also called action potential.
Nerve impulse
A member of a family of membrane-spanning proteins with molecular masses ranging from 30 to 42 kd. Each connexin molecule appears to have four membrane-spanning helices. Connexin is a component of gap junctions.
Connexin
a high-resistance seal formed between a pipette and a small patch of plasma membrane required for use in the patch-clamp technique.
Gigaseal
A protein passage in a membrane that can transport a molecule from one compartment to another against a concentration gradient; pumps undergo a cycle of conformational changes that alter the affinity of the binding site for the transported molecule, and the eversion of the molecule during the cycle is driven by expenditure of free energy. Also called active transporters.
Pump
small, diffusible molecules like acetylcholine that mediate the passage of nerve impulses across the synapse.
Neurotransmitter
The process in which carriers utilize the gradient of an ion to drive the transport of another molecule against its gradient.
secondary active transport
An enzyme that hydrolyzes ATP to generate ionic gradients by pumping Na+ out of the cell and K+ into the cell.
Na+ -K+ pump (Na+ -K+ ATPase)
The space between the presynaptic membrane of one nerve cell and the postsynaptic membrane of an adjacent nerve cell.
Synaptic cleft
Veq = -(RT/zF) ln ([X]in/[X]out) where R is the gas constant and F is the Faraday constant (96.5 kJ V&sup-1; mol&sup-1;, or 23.1 kcal V&sup-1; mol&sup-1;) and z is the charge on the ion X (e.g., +1 for X+).
Nernst equation
a transmembrane channel that is opened by the binding of a one or more molecules to a ligand-binding domain of the channel protein.
Ligand-gated channel
Passageways between the interiors of two contiguous cells. Also known as cell-to-cell channels.
Gap junction (cell-to-cell channel)
A class of carriers able to transport a specific species in either direction governed only by concentrations of that species on either side of the membrane.
Uniporter
a region of ion channel proteins that determines the specificity of a particular channel.
Selectivity filter
A transmembrane channel that is opened by membrane depolarization; the sodium and potassium channels of axon membranes are good examples.
Voltage-gated channel
A genetic disorder in which the recovery of the action potential from its peak potential to the resting equilibrium potential is delayed.
Long QT syndrome (LQTS)
