Role of the NaK Pumps

Since the resting membrane potential is less negative than EK, some K+ leaks out of the cell (fig. 6.24). The cell is not at equilibrium with respect to K+ and Na+ concentrations. Nonetheless,

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■ Figure 6.24 The resting membrane potential. Because some Na+ leaks into the cell by diffusion, the actual resting membrane potential is lower than the K+ equilibrium potential. As a result, some K+ diffuses out of the cell, as indicated by the dashed lines.

Equilibrium Potential

3 Na

■ Figure 6.25 The contribution of the Na+/K+ pumps to the membrane potential. The concentrations of Na+ and K+ both inside and outside the cell do not change as a result of diffusion (dashed arrows) because of active transport (solid arrows) by the Na+/K+ pump. Since the pump transports three Na+ for every two K+, the pump itself helps to create a charge separation (a potential difference, or voltage) across the membrane.

3 Na

■ Figure 6.25 The contribution of the Na+/K+ pumps to the membrane potential. The concentrations of Na+ and K+ both inside and outside the cell do not change as a result of diffusion (dashed arrows) because of active transport (solid arrows) by the Na+/K+ pump. Since the pump transports three Na+ for every two K+, the pump itself helps to create a charge separation (a potential difference, or voltage) across the membrane.

the concentrations of K+ and Na+ are maintained constant because of the constant expenditure of energy in active transport by the Na+/K+ pumps. The Na+/K+ pumps act to counter the leaks and thus maintain the membrane potential.

Actually, the Na+/K+ pump does more than simply work against the ion leaks; since it transports three Na+ out of the cell for every two K+ that it moves in, it has the net effect of contributing to the negative intracellular charge (fig. 6.25). This electro-genic effect of the pumps adds approximately 3 mV to the membrane potential. As a result of all of these activities, a real cell has (1) a relatively constant intracellular concentration of Na+ and K+ and (2) a constant membrane potential (in the absence of stimulation) in nerves and muscles of -65 mV to -85 mV.

Define the term membrane potential and explain how it is measured. Explain how an equilibrium potential is produced when potassium is the only diffusible cation. State how the value of the equilibrium potential is affected by the potassium concentrations outside and inside the cell.

Explain why the resting membrane potential is close to, but different from, the potassium equilibrium potential. Suppose a person has hyperkalemia such that the extracellular K+ concentration increases from 5 mM to 10 mM (a potentially fatal condition). Use the Nernst equation to calculate the new EK, and then verbally describe how the resting membrane potential would be changed.

Describe the role of the Na+/K+ pumps in the generation and maintenance of the resting membrane potential.

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Responses

  • robert
    What is the function of Na / K ATPase pump?
    8 years ago
  • miranda
    What is the role of the na /k atpase pump in the maintenance of the rmp?
    8 years ago
  • daniela
    Why is resting membrane potential closer to equilibrium constant of k ?
    8 years ago
  • alberic
    What is the role of the naK pump in intracellular compartment?
    3 years ago

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