Membranes conductance mediated

Examples of membrane conductance mediated by biomolecular/receptor interactions... 

Both oci and (3 adrenoceptors are postsynaptic excitatory heteroreceptors. Their action is mediated via the activation of Ca2+ current. However, different mechanisms are involved Gq-mediated phospholipase C (PLC) activation and Gs-mediated AC stimulation, respectively (Kandel et al., 2000). When they present on glutamate pyramidal neurons, (3-adrenoceptors receptors decrease the Ca2+-activated after-hyperpolarization K+ influx, making the neurons more responsive for excitatory inputs. The a] adrenoceptors, however, increase membrane conductance and make the pyramidal cells less excitable (Devilbiss and Waterhouse 2000). 

Composition of electroporation buffer is an important factor affecting electroporation yields. Ionic strength of cell suspension medium needs control, which determines resistance of the cell suspension and resultant RC time constant of the field pulse. Medium supplemented with Ca and Mg in mM concentration range is found to promote efficiency of transformation and cell viability. Erythrocytes electroporated in isotonic buffer in the presence of EDTA or membrane specific drugs showed significant modification in hemolysis response to electroporation [33,34]. Use of square wave pulse removes the medium conductivity mediated effects on cell/tissue electroporation outcome. Generally, cells are pulsed in suspensions of sucrose, mannitol, or sorbitol. Electroporation as well as incubation of pulsed cells can be carried out in medium containing usual cell culture recipes. 

Freezing and melting of lipid bilayers greatly alters the conductance mediated by a carrier, because it influences its mobility in the membrane. In contrast, the conductance induced by a channel former is not influenced158. Similarly, an increase of the membrane viscosity, by addition of cholesterol, reduces carrier-, but not channel- mediated conductance278,217. ... 

Effects of the enniatins at lipid bilayers have been studied by several groups133,197,268>28s), Considerably higher concentrations of these antibiotics are required to obtain membrane conductance and potential values comparable with those induced by valinomycin and the macrotetrolides. Ivanov et al. observed first, second, and third power dependence of membrane conductance on enniatin B concentration, but only, first power dependence on the concentration of bis-enniatin B (cf. Section 5.1). They concluded that complexes with 1 1,2 1, and 3 2 carrier-cation stiochiometry are involved in the ion transport mediated by enniatin B and beauvericin. In the limiting case, stacking of many enniatin complex molecules can be postulated, which could lead to a channel mechanism of cation transfer by enniatin133. ... 

The affinity of both toxins is a few nanomolar in each example, while the density of sodium channels varies considerably. For nerve fibres, there is a rough relationship between fibre diameter and channel density. It is not possible to make direct measurements of membrane conductance in small fibres, like those of the garfish olfactory nerve. Both in frog muscle and squid axon the channel conductance is a few fJicomho. This indicates that the turnover numbers at these channels are greater than one could reasonably expect from carrier-mediated transport, yet the turnover is less than at a single gramicidin pore or an ion channel in a muscle end-plate (see p. 7). These latter two, however, lack the ionic... 

Although the whole-cell membrane is non-conductive, there are several redox proteins anchored on/in the membrane that confer nano-scale conductivity to the membrane and directly enable electron transfer across the cell membrane. These proteins usually assemble together in the periplasm and/or on/across the outer-surface membrane and act as an electron transfer chain to relay the electron across the membrane. For example, the membrane-bound electron transfer chain of Shewanella oneidensis is a trans icosa-heme complex, MtrCAB, that can move electrons across the membrane. The MtrC is a decaheme cytochrome located on the outside of the outer cell membrane that mediates the electron transfer to the extracellular substrate e.g, solid electrode). MtrAB is the transmembrane electron transfer module that is responsible for electron transport from the periplasm to MtrC. More interestingly, recent findings indicates that this electron conduit is capable of reverse electron transfer, ie., electron up-take from extracellular electrodes. ... 

Adenosine is produced by many tissues, mainly as a byproduct of ATP breakdown. It is released from neurons, glia and other cells, possibly through the operation of the membrane transport system. Its rate of production varies with the functional state of the tissue and it may play a role as an autocrine or paracrine mediator (e.g. controlling blood flow). The uptake of adenosine is blocked by dipyridamole, which has vasodilatory effects. The effects of adenosine are mediated by a group of G protein-coupled receptors (the Gi/o-coupled Ai- and A3 receptors, and the Gs-coupled A2a-/A2B receptors). Ai receptors can mediate vasoconstriction, block of cardiac atrioventricular conduction and reduction of force of contraction, bronchoconstriction, and inhibition of neurotransmitter release. A2 receptors mediate vasodilatation and are involved in the stimulation of nociceptive afferent neurons. A3 receptors mediate the release of mediators from mast cells. Methylxanthines (e.g. caffeine) function as antagonists of Ai and A2 receptors. Adenosine itself is used to terminate supraventricular tachycardia by intravenous bolus injection. 

In series with a desolvation energy barrier required to disrupt aqueous solute hydrogen bonds [14], the lipid bilayer offers a practically impermeable barrier to hydrophilic solutes. It follows that significant transepithelial transport of water-soluble molecules must be conducted paracellularly or mediated by solute translocation via specific integral membrane proteins (Fig. 6). Transcellular permeability of lipophilic solutes depends on their solubility in GI membrane lipids relative to their aqueous solubility. This lumped parameter, membrane permeability,... 

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