1. Packaging Life: The Origin of Ion-Selective Channels
Clay M. Armstrong 
Biophysical Journal 
Volume 109, Issue 2, Pages (July 2015)
DOI: /j.bpj
Copyright © 2015 Biophysical Society Terms and Conditions

2. Figure 1
A mitochondrion. The outer wall is derived from the mitochondrion’s bacterial ancestry, and is relatively freely permeable. Permeability of the bilipid layer is severely restricted: it is impermeable to most ions. The internal membrane voltage (−140 mV) is relative to the voltage of the surrounding cytoplasm. To see this figure in color, go online.
Biophysical Journal  , DOI: ( /j.bpj )
Copyright © 2015 Biophysical Society Terms and Conditions

3. Figure 2
A chemiosmotic bacterium in sea water. Equilibrium ion concentrations are shown for a freely permeable membrane and (in italics) for a membrane selectively permeable to K+ and Cl−. To see this figure in color, go online.
Biophysical Journal  , DOI: ( /j.bpj )
Copyright © 2015 Biophysical Society Terms and Conditions

4. Figure 3
Approximate ion concentrations outside and inside an animal cell, drawn as a neuron. The dark ovals are mitochondria that produce ATP. The Na/K pump uses ATP to pump 3 Na+ ions outward and 2 K+ ions inward in each cycle. Efflux of K+ down its concentration gradient through K+ channels establishes a membrane voltage (Vm) of ∼−70 mV. The value Vm is positive relative to the equilibrium potential of K+ (∼−92 mV) because of inward leakage of Na+ and other cations. Pumps are essential to keep the internal concentrations of the leaking cations low. To see this figure in color, go online.
Biophysical Journal  , DOI: ( /j.bpj )
Copyright © 2015 Biophysical Society Terms and Conditions