The Membrane as a Transporter, Ion Channels and Membrane Pumps - Membrane Biophysics, Biological and Medical Physics, Biomedical Engineering - page 52

Fig. 4.1 A lipid bilayer membrane exists with an average constant thickness unless a random
membrane protein or an ordered channel induces bilayer deformations. In a , a plain lipid bilayer
membrane has been schematized. A lipid bilayer behaves like a barrier against ion flow across the
membrane. In b , a lipid bilayer membrane with a possible inactive ion channel (in red color ) within
it has been schematized. In this case, despite the presence of an ion channel, the lipid bilayer still
behaves as a barrier against ion flow across the membrane. The channel in this case is apparently
considered to be an inactive or non-transporting agent. In c , a lipid bilayer membrane with a possible
active ion channel has been schematized. In this case, unlike in the cases represented by ( a )and( b ),
the bilayer conducts ions across the membrane. A decrease or increase in bilayer thickness near the
channel interface as the channel undergoes a conformational transition from closed to open states or
vice versa is an important hypothesis in this pictorial representation. A structural change (especially
size) in the channel forming agents is also a theoretical prediction. These schematic diagrams have
been drawn in light of the gating mechanisms observed in mechanosensitive channels in model
membranes [ 39 ]