Q1. Extracellular Na+ is higher than intracellular Na+. If membrane potential were to reach the equilibrium potential for Na+ in which direction would the net Na+ movement be? (1 mark) Inward Outward No net movement Varies by cell Na+ would not move across the membrane Q2. The Donnan effect in a cell is due to: (1 mark) (a) The number of ion channels that are gated by osmotic pressure (b) The number of large impermeant anions trapped inside the cell (c) The number of active transport proteins in the cell membrane (d) The equilibrium potential for chloride for the cell Q3. If a solution contains 0.1 M glucose along with 0.15 M NaCl, calculate the osmolarity of this solution? (3 marks) Q4. A cell is placed into an extracellular solution that has the same osmolarity. However, one of the ions in the extracellular solution is able to move across the cell membrane into the intracellular fluid. After a period of time, the cell would be altered in a manner that would lead one to call the extracellular solution into which the cell was placed _______? Q5. Draw a curve that describes the relationship between the probability or fraction of time that an ion channel is opened and the total current through a population of cells in a particular membrane. (3 marks) Q6. The table below shows the current recorded from patch clamp experiments on potassium channels in cultured rabbit lacrimal gland cells at different stimulating membrane potentials. Q7. Calculate the osmotic pressure of a 1 M KCl solution at room temperature (25ºC) using the gas constant equal to 0.082 L atm K-1mol-1. Q8. 0.500g haemoglobin was dissolved in enough water to make 100.0mL of solution. At 25oC the osmotic pressure was found to be 1.78 x 10-3 atm. Calculate the molecular mass (formula weight) of the haemoglobin. R = 0.0821 L atm K-1mol-1 (gas constant). Q9. The permeability coefficient of molecular oxygen (mass 32Da) is 2.5 x 10-9 m/s at 20˚C. The permeability coefficient of glucose (mass 180Da) is 0.52 x 10-9 m/s at 20˚C. Now, assuming that both molecules have the same concentration gradient, and the membrane’s permeability to both molecules is effectively equal, which of these will diffuse faster from the blood stream to surrounding extra vascular space? Q10. A human red blood cell has a membrane surface area of about 64µm2 and a membrane thickness of about 130 Aº. If the concentration of urea in the extracellular fluid is 1mM, and its intracellular concentration is 0.5mM, calculate the flux of urea in µmoles/sec across the red blood cell membrane. Assume that the diffusion coefficient of urea is 1 x 10-8 cm2/sec. Q11. During the course of a neurosurgical procedure a drug is applied to the surface of the brain in order to inhibit the activity of a group of neurons that lie 2mm below the surface. Approximately how long will it take the drug to diffuse from the surface to those neurons? Assume the diffusion coefficient of the drug in brain tissue is 2 x 10-4 cm2/sec. Q12. If D = 4 x 0.0001 cm2/sec (for oxygen through water), how long would it take the oxygen to diffuse 1 mm below the surface of a still pond? Q13. You patch clamp the soma of a neuron in cell-attached mode. With TTX in the pipette, you measure a current of 336pA from the patch clamped space of the membrane. The microscopic current for K+ is measured at 16pA under the current conditions. Given that the probability of K+ channels being opened is 0.60 at the Vm you have used, how many K+ channels exist within the patch clamped area? Q14. Calculate the membrane potential (Vm) of a cell, given the following resistances and equilibrium potentials. Need to show all calculations. EK = – 90mV, RK = 0.5 x 106 Ω, ENa = 70mV, RNa = 0.5 x 106 Ω Q15. Calculate the membrane potential (Vm) and current (I) at the peak of an action potential, and determine the individual sodium and potassium currents given the following conductance’s and equilibrium potentials. Need to show all calculations. EK = – 72mV, gK = 0.25, ENa = 63mV, gNa = 1.0 Q16. . If EK = -94 mV and VM = -76 mV what will be the direction and magnitude of the ECDF? Q17. A cell has a membrane potential of – 68 mV with the concentration of an ion [X-] inside (35 mM) and concentration outside (180 mM). What will be the direction and magnitude of the ECDF? Q18. If ENa = 66 mV and VM = -50 mV what will be the direction and magnitude of the ECDF? Q19. Draw an I-V plot for two different non-voltage dependent ionic currents IA and IB under the following conditions: When the conductance (g) is the same (2pS) for both ions A and B, but equilibrium potentials (-70mV for A, -50mV for B respectively) are different. Label the axes. (5 marks) 2. When the equilibrium potentials for both are the same (-40mV) but they have different conductances (2pS for A, 4pS for B respectively). Label the axes. Q20. A membrane, which is only permeable to water, separates a sucrose solution from a glucose solution in water. The sucrose and glucose concentrations at the beginning are 155 mol.m-3 and 55 mol.m-3 respectively and the temperature is 20ºC. Use R = 8.314 J K-1mol-1 for the gas constant. Calculate the size of the hydrostatic pressure (expressed in atmospheres) necessary to block any movement of water. Should the hydrostatic pressure be applied over the sucrose or over the glucose solution? Q21. Due to an electrolyte imbalance, a patient has following intracellular and extracellular concentrations of potassium: [K+]in = 145mM and [K+]out = 10mM in the neurons. Using the Nernst Equation calculate the change in potassium equilibrium potential in the neurons of the diseased patient with the electrolyte imbalance. Will it be easier or more difficult to generate an action potential in the diseased neuron compared to the normal neuron? Assume that in a non diseased state the intracellular and extracellular concentrations of potassium are: [K+]in = 145mM and [K+]out = 5mM Q22. Consider a situation where K+ ion has an intracellular fluid (ICF) concentration of 320 mM and an extracellular fluid (ECF) concentration of 35 mM. What will be the direction and magnitude of the ECDF acting on K+ at Vm = – 82 mV? Q23. Why would failure to transport chloride ions across the airway epithelium cause secreted mucus to be thick? Q24. What is the Donnan Effect? Two solutions are separated by a membrane permeable to sodium and chloride ions, the concentrations on side 1 are sodium = 100 mM and proteins = 100mM and the concentrations on side 2 are sodium = 100 mM and chloride = 100 mM. At steady state approximate the concentrations of the different species and describe the different forces contributing to this steady state.
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