Lecture 5 - Electrochemical gradients and equilibrium potentials

When do ions move across cell membrane and how?

• in resting state, ions are moved across the cell membrane through leak ion channels

• 2K for 3 Na

• ions move across cell membrane of excitable cells

• difference in voltage in and out of cell is result of different concentration of ions and is referred to as resting membrane potential of cell

What do you think MOSTLY DETERMINES the set membrane potential of a resting excitable cell?

• the leak of potassium ions across the cell membrane

• at rest, membrane of excitable cells = mostly permeable to potassium ions

  • leak channels are most abundant and open

What is the resting membrane potential?

• it is the difference in ion concentration across the cell membrane of an excitable cell at rest

What is the electrochemical gradient?

• a combination of both chemical and electrical forces act upon ions across a cell membrane

What is equilibrium potential?

• the membrane potential when the electrical gradient exactly balances chemical gradient and there is NO NET movement of that ion

• all ions move to attempt to reach equilibrium potential

How do you calculate equilibrium potential for an ion?

• use NERNST equation

What is the simplified NERNST equation?

• to convert natural logarithm (ln) to base 10 log —→ multiply by 2.3