Channel complexes

Anderson D T, Schwartz R L and Todd M W and Lester M I 1998 Infrared spectroscopy and time-resolved dynamics of the ortho-Hj-OH entrance channel complex J. Chem. Phys. 109 3461-73... 

Loomis R A and Lester M I 1997 OH-H2 entrance channel complexes Ann. Rev. Phys. Chem. 48 643-73... 

Fig. 15. Drug binding sites associated with the GABA receptor—channel complex where (— -) represents the carbon backbone of GABA agonists.

FIGURE 17.28 Image reconstructions of the junctional channel complex of a foot structure. (Photo courtesy of Sidney FIAscher, Vanderbilt University)... 

Every SUR subunit carries one site for inhibitory drugs, and hence there are four of these sites per channel complex. Analogous to ATP-induced inhibition (see earlier) occupation of just one of these sites is sufficient to close the channel. This effect is mediated by egalizing Mg-nucleotide-induced channel activation. 

Big-conductance Ca2+ sensitive K+ (BKca) channels are activated by calcium surge and membrane depolarization. BKCa channels are specifically blocked by iberiotoxin and less selectively by charybdotoxin. BKCa channels are composed of pore-forming a and auxiliary (3 subunits. Both BKCa,a andBKca, 3 subunits as well as their efficient coupling in the heteromultimeiic formation of BKca channel complexes are important for the function of BKCa channels. 

In the case of L-type Ca2+ channels, they also carry binding sites for Ca2+ antagonist drugs. The accessory a2-5, p, and y subunits stabilize Ca2+ channel function and support its targeting to the plasma membrane. Notably other proteins can associate with the channel complex allowing the formation of signaling complex important for channel targeting and modulation. 

Research in this area advanced in the 1970 s as several groups reported the isolation of potent toxins from P. brevis cell cultures (2-7). To date, the structures of at least eight active neurotoxins have been elucidated (PbTx-1 through PbTx-8) (8). Early studies of toxic fractions indicated diverse pathophysiological effects in vivo as well as in a number of nerve and muscle tissue preparations (reviewed in 9-11). The site of action of two major brevetoxins, PbTx-2 and PbTx-3, has been shown to be the voltage-sensitive sodium channel (8,12). These compounds bind to a specific receptor site on the channel complex where they cause persistent activation, increased Na flux, and subsequent depolarization of excitable cells at resting... 

Figure 1 highlights several general features of PESs for reactions. After forming the entrance channel complex, the metal typically inserts into a bond in... 

The mechanism that has been developed for the conversion of methane to methanol by FeO+ is an excellent example of the synergy between experiment and theory. This mechanism includes two key concepts concerted reaction involving the critical [HO—Fe—CH3] insertion intermediate and two-state reactivity. The reaction proceeds as follows electrostatic interaction between FeO+ and methane produces the [OFe- GHJ entrance channel complex. 

Figure 4. Schematic potential energy surface for the reaction of FeO" " with methane. The sohd line indicates the sextet surface the quartet surface is shown with a dotted line, in each case leading to the production of Fe + CH3OH. The dashed line leads to formation of FeOET + CH3. The pathway leading to the minor FeCH2" + H2O channel is not shown. Schematic structures are shown for the three minima the [OFe CHJ entrance channel complex, [HO—Fe—CH3] insertion intermediate, and Fe" (CH30H) exit channel complex. See text for details on the calculations on which the potential energy surface is based.

Figure 11.7 Presumed arrangement of GABAa receptor subunits to form a receptor-channel complex, (a) Diagrammatic representation of an individual subunit with four transmembrane regions, extracellular sites for glycosylation and a site for phosphorylation on the intracellular loop between M3 and M4. (b) Association of five subunits to form a central ionophore bounded by the M2 region of each subunit. The suggested stoichiometry of the most widely expressed form of receptor is 2a, 2 and ly. Shown below are the possible subunit combinations of one such benzodiazepine-sensitive receptor together with a benzodiazepine-insensitive receptor in which the 7 subunit is replaced by a c5, and a ti-containing receptor with four different subunit types...

Kuhse, J, Betz, H and Kirsch, J (1995) The inhibitory glycine receptor architecture, synaptic localization and molecular pathology of a postsynaptic ion-channel complex. Curr. Opin. Neurobiol. 5 318-323. 

Our discussion of complex formation in electron-ion recombination, field effects, and three-body recombination has perhaps posed more questions than it has answered. In the case of H3 recombination, the experimental observations suggest but do not prove that complex formation is an important mechanism. Three-body recombination involving complex formation is not likely to have much effect on the total recombination coefficients of diatomic ions, but it may alter the yield of minor product channels. Complex formation may be most prevalent in the case of large polyatomic ions, but there is a serious lack of experimental data and theoretical calculations that can be adduced for or against complex formation. 

Fagg, G.E., Phencyclidine and related drugs bind to the activated JV-methyl-D-aspartate receptor-channels complex in rat membranes, Neurosci. Lett., 76, 221, 1987. 

Riven, I., Iwanir, S. and Reuveny, E. (2006). GIRK channel activation involves a local rearrangement of a preformed G protein channel complex. Neuron 51, 561-73. 

Jerng, H.H., Kunjilwar, K., and Pfaffinger, P.J. (2005) Multiprotein assembly of Kv4.2, KChIP3 and DPP10 produces ternary channel complexes with ISA-like properties./. Physiol. 568, 767-788. 

The answer is b. (Hardman, pp 365—367J Benzodiazepines, such as diazepam, bind to the GABA receptor/ion channel complex, enhancing GABA-induced Cl" currents related to more frequent bursts of Cl channel opening by GABA. 

FIGURE 50-6 A model for chemosensory transduction in vomeronasal sensory neurons. The individual steps are detailed in the text. In contrast to the transduction cascade in OSNs, the mechanism of vomeronasal transduction is less well characterized. Vomeronasal neurons express either V1R or V2R receptors and either Got. or Ga0, respectively. The TRPC2 channel subunit is expressed in all vomeronasal neurons, and may be part of a multimeric channel complex. Ca2+ions are represented as purple balls, Na+ ions as blue balls. VR, vomeronasal receptor (VlRorV2R) PIP2, phospha-tidylinositol 4,5-bishphosphate IP, inositol 1,4,5-trisphosphate DAG, diacylglycerol. 

Albuquerque EX, Akaike A, Shaw KP, Rickett DL. The interaction of anticholinesterase agents with the acetylcholine receptor-channel complex. Fundam. Appl. Toxicol. 4 S27-S33, 1984. 

Albuquerque EX, Aracava Y, Cintra WM, Brossi A, Schonenberger B, Deshpande SS. Structure-activity relationship of reversible cholinesterase inhibitors activation, channel blockade and stereospecificity of the nicotinic acetylcholine receptor-ion channel complex. Braz. J. Med. Biol. Res. 21 1173-1196, 1988. 

Kitazawa T, Kobayashi S, Horiuti K, Somlyo AV, Somlyo AP 1989 Receptor coupled, permeabilized smooth muscle role of the phosphatidylinositol cascade, G proteins and modulation of the contractile response to Ca2+. J Biol Chem 264 5339-5342 Lopez-Lopez JR, Shacklock PS, Balke CW, Wier WG 1995 Local calcium transients triggered by single L-type calcium channel currents in cardiac cells. Science 268 1042-1045 Marks AR, Fleischer S, Tempst P 1990 Surface topography analysis of the ryanodine receptor/ junctional channel complex based on proteolysis sensitivity mapping. J Biol Chem 265 13143-13149... 

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