Meta-Biol

• Pathways

Ion channels that mediate sensations such as pain, warmth, cold, taste pressure and vision. Channels that mediate these sensations include acid-sensing ion channels (ASICs) (Wang & Xu 2011, Qadri et al. 2012, Deval et al. 2010) and the transient receptor potential channels (TRPCs) (Takahashi et al. 2012, Numata et al. 2011 in "TRP Channels" Zhu, MX editor, CRC Press, 2011, Ramsey et al. 2006, Montell 2005). Many channels are sensitive to changes in calcium (Ca2+) levels, both inside and outside the cell. Examples are protein tweety homologs 2 and 3 (TTYH2, 3) (Suzuki 2006), bestrophins 1-4 (BEST1-4) (Sun et al. 2002, Tsunenari et al. 2003, Kunzelmann et al. 2009, Hartzell et al. 2008) and ryanodine receptor tetramers (RYRs) (Beard et al. 2009).

Ion channels mediate the flow of ions across the plasma membrane of cells. They are integral membrane proteins, typically a multimer of proteins, which, when arranged in the membrane, create a pore for the flow of ions. There are different types of ion channels. P-type ATPases undergo conformational changes to translocate ions. Ligand-gated ion channels operate like a gate, opened or closed by a chemical signal. Voltage-gated ion channels are activated by changes in electrical potential difference at the membrane (Purves, 2001; Kuhlbrandt, 2004).

By definition cells have a critical separation between inner (cytoplasmic) and outer (extracellular) compartments. This separation provides for protection, gradient assembly, and environmental control but at the same time isolates the interior compartments of the cell from energy resources, oxygen, and raw materials. Cells have evolved a myriad of mechanisms to regulate, and enable transportation of small molecules ascross plasma membranes and between cellular organelle compartments within cells.