The following concentrations of Na+ and K+ ions: [Na+]o = 120 mM, [Na+]i = 6 mM, [K+]o = 2 mM, and [K+]i = 150 mM. Assuming that the further at the peak of the action potential, PK : PNa is 1 : 12. Calculate (Vm) at the peak of the action potential
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The following concentrations of Na+ and K+ ions: [Na+]o = 120 mM, [Na+]i = 6 mM,
[K+]o = 2 mM, and [K+]i = 150 mM.
Assuming that the further at the peak of the action potential, PK
: PNa is 1 : 12.
Calculate (Vm) at the peak of the action potential
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- Conformational changes in channel proteins brought about by voltage changes are responsible for opening and closing Na+ and K+ gates during the generation of an action potential. (True or false?)Given that the extracellular concentration of Cl- is approximately 120 mM, what is the intracellular concentration if the Nernst potential for Cl- is 39 mV. (T=298 K, R=1.987 cal/K·mol, F=23,062 cal/mol·V)At the peak of the action potential, Vm is approximately -65 mV. Assuming normal intracellular and extracellular K+ concentrations (refer to the table), (1) calculate the driving force (in mV) that acts on K+ ions and (2) use the information obtained in part 1 to determine the direction in which K+ ions will flow (i.e., into the cell or out of cell)
- The typical distribution of K+ and Na+ ions inside and outside the cell is: [K+]in = 150 mM; [K+]out = 5 mM; [Na+]in = 10 mM; [Na+]out = 150 mM What are reversal potentials for Na+ and K+ at 25oC ? What should be the ratios of PNa/PK at (i) rest (-60 mV) and (ii) during the action potential (+20 mV) to generate a spike from -60 to +20 mV. Use the short form of Goldman equation.Calculate the equilibrium membrane potentials to be expected across a membrane at 37 ∘C, with a NaCl concentration of 0.50M on the "right side" and 0.08 M on the "left side", given the following conditions. In each case, state which side is (+) and which is (−). (a)Membrane permeable only to Na+.The ion flows across neuronal membranes at rest and duringan action potential do not significantly change bulk ionconcentrations, except for that of Ca2+ ions. Resting Ca2+ ionconcentrations in cells are usually about 10–7 M, and Ca2+ ionsexert physiological effects at concentrations of perhaps 10–5 M.Explain why relative changes of intracellular [Ca2+] are muchgreater than for, say, [Na+] (12–50 mM).
- Calculate the equilibrium membrane potentials to be expected across a membrane at 37 ∘C, with a NaCl concentration of 0.50 M on the "right side" and 0.08 M on the "left side", given the following conditions. In each case, state which side is (+) and which is (−). Membrane equally permeable to both ions.Assuming that the resting physiological cytoplasmic and extracellular concentrations of Ca2+ (Ca2+o=1 mM, Ca2+i=0.0001 mM ), Determine the Ca2+ equilibrium potential (VCa)Calculate the free energy of transport for the movement of potassium by the sodium/potassium pump under normal physiological conditions: 4 mM serum potassium, 135 mM intracellular potassium, 37.1 °C, and resting potential -82 mV. Express your answer in kJ/mol. Show all work. Calculate the free energy of transport for the movement of potassium by the sodium/potassium pump under disturbed conditions of 2 mM serum potassium. Assume all other parameters remain the same. Express your answer in kJ/mol. Show all work. What factors could limit the continued action of the sodium/potassium pump when only 2 mM potassium is present in the blood plasma? Note that under normal physiological conditions, the cell interior contains 11 mM sodium and the blood contains 140 mM sodium.
- With regard to Na+ and K+ equilibrium potentials and the resting and active membrane potentials, write down (a- D the directions of the forces indicated, acting on the ion in the table below under the respective condition(s). NB the examples given. lon Condition Electrical/Chemical force Direction of force Chemical e.g....inward.. ****** Na ENa+ = + 60 mV Electrical a. Chemical e.g. ...outward.. EK+ =- 90 mV Electrical b. Chemical C. Na" Emp = 0 mV Electrical d. Chemical K+ Emp =-20 mV ElectricalCalculate the driving force for Na+, K+, and Ca2+ current in a neuron under physiological conditions.The normal concentrations for intracellular and extracellular potassium in a neuron are [K+]in = 150 mM and [K+]out = 5 mM, respectively. Due to an electrolyte imbalance, a patient has the following intracellular and extracellular concentrations of potassium: [K+]in = 140 mM and [K+]out =2 mM. Using the Nernst equation (Chapter 4), calculate the equilibrium potential for potassium in the cells with normal K+ distributions and of the diseased patient. Refer back to Question #1. Will it be easier or more difficult to generate an action potential in the diseased neuron as compared to the normal neuron? Why?
