Gated ion channel

The equilibrium constant for channel opening can be expressed in terms of the ratio of the probabilities that the channel is in the open or closed states, 

Applying an electrostatic field can shift the equilibrium toward the open state. According to Equation (21.18), the work performed by a field in ahgning a dipole is 

We have used E = -qj/d to convert from the field E to the voltage difference across the membrane (i// is the potential of the lower solution relative to 0 in the upper solution) because the solutions on the two sides of the membrane act as parallel plate electrodes across a membrane of thickness d. Because the quantities A cos 0 = cos dopen - cos dcioscd and q and ( may not he known independently, we can reduce the number of unknown parameters in the model by defining an effective charge ZeffC, 

The ion flow through the channel is proportional to the fraction of time that the channel is open, which you can compute by substituting Equation (22.28) into (22.27) and then into Equation (22.26) to get 

Electric fields can not only move charged molecules, they can also shift chemical equilibria. 

---

Newel experimental approaches to anxiety therapy include ligands interacting with the ligand-gated ion channels that are selectively activated by nicotine, C qH 4N2 (87), the well-known active ingredient of cigarettes which has anxiolytic actions (42). Cholecystokinin B receptor ligands, specifically the dipeptoid, CI-988 [130404-91 -0] 02 1142 40 (88) have demonstrated anxiolytic activity ia preclinical models (43). 

Fig. 1. Model of a ligand gated ion channel (LGIC) where (a) is the structure of a generic LGIC subunit showing the two cysteine (Cys) residues common to all LGIC subunits, and (b) shows the arrangement of five such subunits as a pentamer having psuedo-cyclic symmetry delineating a gated, fluid-filled...

Kaupp UB, Seifert R (2002) Cyclic nucleotide-gated ion channels. Physiol Rev 82 769-824... 

Krasowski MD, Harrison NL (1999) General anaesthetic actions on ligand-gated ion channels. Cell Mol Life Sci 55 1278-1303... 

A number of agonists can act through several receptor classes, e.g., ion channels and G-protein-coupled receptors. To set receptor subtypes permanently linked to ion channels ( ligand-gated ion channels) apart... 

For differentiation of G-protein-coupled receptor sub-types from subtypes permanently linked to ion channels (ligand-gated ion channels) the terms metabotropic versus ionotropic receptors, respectively, are used. Prime examples of metabotropic receptors are given by the lnGlu receptor family of G-protein-coupled glutamate receptors. 

Neurotransmitter transport can be electrogenic if it results in the net translocation of electrical charge (e.g. if more cations than anions are transferred into the cell interior). Moreover, some transporters may direction-ally conduct ions in a manner akin to ligand-gated ion channels this ion flux is not coupled to substrate transport and requires a separate permeation pathway associated with the transporter molecule. In the case of the monoamine transporters (DAT, NET, SERT) the sodium current triggered by amphetamine, a monoamine and psychostimulant (see Fig. 4) is considered responsible for a high internal sodium concentration... 

Nicotine is the main psychoactive ingredient of tobacco and is responsible for the stimulant effects and abuse/ addiction that may result form tobacco use. Cigarette smoking rapidly (in about 3 sec ) delivers pulses of nicotine into the bloodstream. Its initial effects are caused by its activation of nicotinic acetylcholine (nACh) receptors. nACh receptors are ligand-gated ion-channels and pre- and postsynaptically located. Reinforcement depends on an intact mesolimbic dopamine system (VTA). nACh receptors on VTA dopamine neurons are normally activated by cholinergic innervation from the laterodorsal tegmental nucleus or the pedunculopontine nucleus. 

HT3 receptors belong to the ligand-gated ion channel receptor superfamily, similar to the nicotinic acetylcholine or GABAa receptors and share elec-trophysiological and structural patterns. The receptors... 

Synaptic Transmission. Figure 1 Synaptic transmission. The presynaptic terminal contains voltage-dependent Na Superscript and Ca2+ channels, vesicles with a vesicular neurotransmitter transporter VNT, a plasmalemmal neurotransmitter transporter PNT, and a presynaptic G protein-coupled receptor GPCR with its G protein and its effector E the inset also shows the vesicular H+ pump. The postsynaptic cell contains two ligand-gated ion channels LGIC, one for Na+ and K+ and one for Cl-, a postsynaptic GPRC, and a PNT. In this synapse, released transmitter is inactivated by uptake into cells. 

Of the several classes of receptors for endogenous chemical signals [3], two are used as postsynaptic receptors in synaptic transmission ligand-gated ion channels (LGICs) and G protein-coupled receptors (GPCRs Fig. 1). Due to the large number of transmitters and the existence of several receptor types for almost all, postsynaptic receptor activation is the most diversified step of synaptic transmission. Table 1 shows selected neurotransmitter receptors. 

Inhalants appear to have significant effects on a superfamily of ligand-gated ion channels, including the GABAj receptor, the glycine receptor, the nico-... 

---