Department of Health, Nutrition, and Exercise Sciences WCR Chapter 3: Cells • Plasma membrane: structure • Plasma membrane: transport • Resting membrane potential • Cell-environment interactions • Cytoplasm • Nucleus • Cell growth & reproduction • Extracellular materials, developmental aspects
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Department of Health, Nutrition, and Exercise Sciences WCR Chapter 3: Cells Plasma membrane: structure Plasma membrane: transport Resting membrane potential.
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Department of Health, Nutrition, and Exercise Sciences WCR
Department of Health, Nutrition, and Exercise Sciences WCR
Resting membrane potential•All living cells at rest•Voltage inside is negative relative to outside•Ranges from –50 to –100 mV in different cells•Results from separation of oppositely charged particles (ions) across the membrane•A form of stored (i.e. potential) energy•Energy comes from active transport of ions (mainly pumping Na+ out of cells and K+ into cells)
Human adipocyte.Yeh & Shi (2010), WIREs Nanomed Nanobiotechnol 2: 176–188.
Generation and maintenance of resting membrane potential
5. Concentration gradient (chemical force) pushes K+ out. Negative intracellular voltage (electrical force) pulls K+ in. Net force is the electrochemical gradient.
6. When intracellular voltage is negative enough that electrical and chemical forces on K are (approximately) balanced, there is hardly any net force on K+, and that is the RMP.
7. Steady state is maintained because active transport of Na+ out and K+ in is equal and opposite to the residual leakage of Na+ in and K+ out.
K+ diffuses “down” its steep concentration gradient (out of cell) via leakage channels. Loss of K+ results in a net negative charge, and therefore negative voltage, inside cell.
K+ also moves into cell because it is attracted to negative charge inside cell.
A stable negative membrane potential (-50 to -100 mV) is established when K+ movement out of cell equals K+ movement into cell. At this point, chemical concentration gradient for K+ exit is equal* & opposite to electrical gradient for K+ entry.
Potassiumleakagechannels
Protein anion (unable tofollow K+ through themembrane)Cytoplasm
Extracellular fluid
*Not exactly equal. Actual RMP is slightly more + than the voltage that would put K+ at equilibrium, so there is a small residual outflow of K+. This is counteracted by the Na-K pump.