Ion channel selectivity

Cell membranes contain selective ion channels that are highly discriminatory for potassium ions, sodium ions, calcium ions, and the proton. For instance, the highly selective potassium channels of nerves show selectivity for ions as Li < Na K > Rb > Cs, and calcium channels show selectivity as Mg Ca > Sr > Ba. Ion selection operates on the basis of size and repulsion, not... 

Nicotinic receptors are part of a transmembrane polypeptide whose subunits form cation-selective ion channels (see Figure 2-9). These receptors are located on plasma membranes of postganglionic cells in all autonomic ganglia, of muscles innervated by somatic motor fibers, and of some central nervous system neurons (see Figure 6-1). 

Kirichok, Y., Krapivinsky, G. and Clapham, D. E., 2004, The mitochondrial calcium uniporter is a highly selective ion channel. Nature 427, 360-4. 

Zhuang, L., Peng, J. B., Tou, L., Takanaga, H., Adam, R. M., Hediger, M. A. and Freeman, M. R., 2002, Calcium-selective ion channel, CaTl, is apically localized in gastrointestinal tract epithelia and is aberrantly expressed in human malignancies. Lab Invest 82, 1755-64. 

Gofa A, Davidson RM. 1996. NaF potentiates a K+-selective ion channel in G292 osteoblastic cells. J Membr Biol 149 211-9. 

Possibly due to the variety of their pAj values, claudins appear to confer selectivity in the paracellular transport of ions, with TJ in most epithelia resembling cation-selective ion channels (Powell 1981). As the extracellular loops of occludin remain uncharged at physiological pH, it is assumed that this selectivity is caused primarily by claudins (Yu et al. 2003). In recent in vitro studies, TJ were shown to have size and charge selectivity, dependence on ion concentration and competition, and pH (Tang and Goodenough 2003). 

Postsynaptic, inhibitory, opens a Ch-selective ion channel Presynaptic, inhibitory, reduces calcium entry Postsynaptic, inhibitory, increases K+ conductance Postsynaptic, inhibitory, opens a Ch-selective ion channel... 

Postsynaptic, excitatory, opens an Na+,K+-selective ion channel Postsynaptic, excitatory, opens an Na+,K+-selective ion channel Postsynaptic, excitatory, opens an Na+,K+,Ca2+-selective ion channel... 

Wright Al et al (2001) Novel resordn[4]arenes as potassium-selective ion-channel and transporter mimics. Chem Eur 17 3474-3481... 

The genome in influenza A and B types is enclosed within an outer lipoprotein envelope (Fig. 17.1). The Ml protein lines the inside of the envelope and is chemically bound to the ribonucleoprotein [14], The Ml protein plays an important role in the mediation of nuclear export of viral ribonucleoproteins and also in virus assembly and budding during the infectious cycle [5, 14, 15], An antigenic protein M2, which functions as a proton-selective ion channel, is present in the viral membrane of influenza A viruses [6, 13], In influenza B, the ion channel activity to aid virus uncoating in the endosome is carried out by the similar integral membrane protein BM2 [11],... 

In contrast, amiodarone and sotalol are effective in most supraventricular and ventricular tachycardias. Amiodarone displays electrophysiologic characteristics consistent with each type of antiarrhythmic drug, ft is a sodium channel blocker with relatively fast on-off kinetics, has nonselec-tive j8-blocking actions, blocks potassium channels, and has slight calcium antagonist activity. The impressive effectiveness and low proarrhythmic potential of amiodarone have challenged the notion that selective ion channel blockade is preferable. Sotalol is a potent inhibitor of outward... 

Nicotinic acetylcholine (ACh) receptors are responsible for transmission of nerve impulses from motor nerves to muscle fibers (muscle types) and for synaptic transmission in autonomic ganglia (neuronal types). They are also present in the brain, where they are presumed to be responsible for nicotine addiction, although little is known about their normal physiological function there. Nicotinic receptors form cation-selective ion channels. When a pulse of ACh is released at the nerve-muscle synapse, the channels in the postsynaptic membrane of the muscle cell open, and the initial electrochemical driving force is mainly for sodium ions to pass from the extracellular space into the interior of the cell. However, as the membrane depolarizes, the driving force increases for potassium ions to go in the opposite direction. Nicotinic channels (particularly some of the neuronal type) are also permeable to divalent cations, such as calcium. 

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