You attempt to generate an IV plot for GABA channels in cultured neurons. You apply pentobarbital and perform voltage steps but see no current at any voltage. Which of the following would explain your findings? Concentration of pentobarbital is too low GABA is not present in your solutions Cl- concentration is equal on both sides of the membrane None of the above
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You attempt to generate an IV plot for GABA channels in cultured neurons. You apply pentobarbital and perform voltage steps but see no current at any voltage. Which of the following would explain your findings?
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Concentration of pentobarbital is too low |
||
|
GABA is not present in your solutions |
||
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Cl- concentration is equal on both sides of the membrane |
||
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None of the above |
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- One of the important uses of the Nernst equation is in describing the flow of ions across plasma membranes. Ions move under the influence of two forces: the concentration gradient (given in electrical units by the Nernst equation) and the electrical gradient (given by the membrane voltage). This is summarized by Ohms law: Ix=Gx(VmEx) which describes the movement of ion x across the membrane. I is the current in amperes (A); G is the conductance, a measure of the permeability of x, in Siemens (S), which is I/V;Vm is the membrane voltage; and Ex is the equilibrium potential of ion x. Not only does this equation tell how large the current is, but it also tells what direction the current is flowing. By convention, a negative value of the current represents either a positive ion entering the cell or a negative ion leaving the cell. The opposite is true of a positive value of the current. a. Using the following information, calculate the magnitude of Na [ Na+ ]0=145mM,[ Na+ ]i=15mM,Gna+=1nS,Vm=70mV b. Is Na+ entering or leaving the cell? c. Is Na+ moving with or against the concentration gradient? Is it moving with or against the electrical gradient?Which of the following statements best describes the features of voltage-gated K+ channels? They consist of 4 subunits, are activated at the same time as voltage-gated Na+ channels, but do not inactivate. They consist of 4 subunits, are activated by depolarisation and close slowly during the refractory period. They have 24 membrane spanning alpha helices, 4 of which have positively charged amino acids which promote a conformational change in the channel following depolarisation. They consist of 4 subunits and are open at rest which causes the resting membrane potential to be close to the K+ equilibrium potential.Patch clamp recording of a single ion channel yields the following results: Holding Potential (mV) Measured Current (pA) -100 -1.0 -50 0.0 0 +1.0 +50 +2.0 +100 +3.0 part a.) Calculate the membrane potential at the instant when a neuron has the following relative permeabilities: PK+ = 1.0, PNa+ = 1.0, PCl- = 1.0. Use the ionic concentration values in the picture included. a.) -12 mv b.) -35mv c.) -60 mv d.) +20 mv e.) 0 mv part b.) What would be the equilibrium potential for K+ in neurons under such circumstances? a.) -11 mv b.) +30 mv c.) +75 mv d.) -35 mv e.) 0 mv part c.) What would be the new resting potential, discounting the effects of non-gated chloride channels (just give an approximate value – no calculation is necessary)? a.) about +20 to +25 mV b.) about -30 to -40 mV c.) about +1 to +5 mV d.) close to ENa+ e.) about -10 to -15 mV
- The rapid upstroke of a SA nodal cell action potential is due to the opening of voltage-gated Na+ channels. answer should clearly state whether or not the statement is correct and then concisely explain why. the answer should be 3-5 sentences and address all of the points in the statement. Here is an example: Both transmembrane carrier proteins and transmembrane channel proteins can mediate active transport of a hydrophilic solute through a cell plasma membrane. This statement is incorrect. Movement of a solute through a channel protein is always passive, whereas carrier-mediated transmembrane transport can be either passive or active. A transmembrane channel protein creates a pore through the membrane allowing for simple diffusion of a hydrophilic solute down a concentration gradient through the membrane. In contrast, transmembrane carrier protein interacts with and ‘escorts’ a hydrophilic solute through the membrane and is capable of transporting a solute against a concentration…Fill in the diagram, your illustration should demonstrate for each phase of the AP: 1. The relative concentration of K and Na 2. The relative voltage across the membrane 3. Any movement across the membrane of K and NA 4. The three kinds of channels in the membrane, and their state (open or closed) 5. Finally, indicate on the graph of the AP which phases correspond to hyper- polarization and which phases correspond to de- polarization Outside Outside Inside Inside Outside Inside Outside 1 Outside Inside InsideSeparately, draw a table using arrows to depict the appropriate magnitude and direction of the forces and ion fluxes at different membrane potentials for a ligand-gated channel that is equally permeable to both ion X+ and ion Y+. The equilibrium potential for ion X+ is -60 mV, and the equilibrium potential for ion Y+ is -20 mV. Which item (a, b, c, or d) best represents the forces and fluxes for a membrane potential of +20 mV? Upwards arrows means outward direction and downwards arrow means inward direction. The length of the arrow determines the magnitude.
- Which of the following statements about voltage gated channels is true? Voltage-gated sodium channels open at a higher (more positive) membrane potential than do potassium-gated channels Voltage-gated sodium channels open at a lower (more negative) membrane potential than do potassium-gated channels Sodium- and postassium-gated channels open at about the same membrane potential, but they have different effects because there are different numbers of the two kinds of channels in neuron cell membranesChloride ions (Cl-) behave a bit differently to Na+ and K+ in that most cells don't have active Cl- transporters. As a result, the concentration gradient for Cl- is not 'set' like it is for Na+ and K+. There are, however, a limited number of Cl- leak channels in the cell membrane. As a result, Eci generally matches resting membrane potential - around - 70mV. Considering this, answer the following questions. If Cl- can cross the cell membrane, is not being actively transported, and membrane potential is -70mV, will there be a concentration gradient for Cl-?Separately, draw a table using arrows to depict the appropriate magnitude and direction of the forces and ion fluxes at different membrane potentials for a ligand-gated channel that is equally permeable to both ion X+ and ion Y+. The equilibrium potential for ion X+ is -60 mV, and the equilibrium potential for ion Y+ is -20 mV. Which item best represents the forces and fluxes for a membrane potential of -40 mV (a, b, c, or d)? Upwards arrows means outward direction and downwards arrow means inward direction. The length of the arrow determines the magnitude.
- Draw the current changes caused by a single voltage gated Potassium channel when the membrane is voltage-clamped at different voltage values (see below). Assume an equilibrium potential for potassium of -70mV and don't worry about exact values for the currents (approximations are fine). Label the axes on the traces and describe how the dynamics of individual voltage gated potassium channels come together to form the macroscopic K+ currents during depolarization. . a. @Resting Membrane Potential = -70 mV b. @Voltage Step = -20 mV c. @Voltage Step = +50mVSeparately, draw a table using arrows to depict the appropriate magnitude and direction of the forces and ion fluxes at different membrane potentials for a ligand-gated channel that is equally permeable to both ion X+ and ion Y+. The equilibrium potential for ion X+ is -60 mV, and the equilibrium potential for ion Y+ is -20 mV. Which item best represents the forces and fluxes for a membrane potential of 0 mV?Draw the current that you would expect to flow during a voltage clamp experiment on a typical neuron. Voltages and time course are shown. Briefly explain why the currents are inward or outward. Be sure to provide scale bars. You should definitely label the Y axis so that the peak current value is obvious. Draw the Na+ current you would expect if there were physiological ionic gradients. Draw the K+ current you would expect if there are physiological ionic gradients. Draw the K+ current you would expect if the bath solution and the intracellular solution are both 125 mM.