Cell membrane channels

Calcium-channel blockers interfere with the inward movement of calcium ions through the cell membrane channels. This results in reduction of myocardial contractility (hence negative inotropes), reduction of cardiac output and arteriolar vasodilatation. The dihydropyridine group, such as nifedipine and amlodipine, which may be used in the management of hypertension, are very effective as arterial vasodilators, whereas diltiazem and verapamil are very effective in reducing atrioventricular conduction. 

Mechanism of Action An antiparasiticagent that inhibits sodium influx through nerve cell membrane channels. Therapeutic Effect Results in delayed repolarization, paralysis, and death of parasites. 

Loewenstein WR Junctional intercellular communicaiton The cell-to-cell membrane channel. Physiol Rev 1981 61 829-913. 

Loewenstein, WR. 1981. Junctional intercellular communication The ceU-to-cell membrane channel. 

Membrane proteins comprise another important class of protein crystallized in 2D. These proteins perform important functions as membrane channels and recognition sites for cells. Unlike the streptavidin crystals, membrane proteins... 

The primary site of action is postulated to be the Hpid matrix of cell membranes. The Hpid properties which are said to be altered vary from theory to theory and include enhancing membrane fluidity volume expansion melting of gel phases increasing membrane thickness, surface tension, and lateral surface pressure and encouraging the formation of polar dislocations (10,11). Most theories postulate that changes in the Hpids influence the activities of cmcial membrane proteins such as ion channels. The Hpid theories suffer from an important drawback at clinically used concentrations, the effects of inhalational anesthetics on Hpid bilayers are very small and essentially undetectable (6,12,13). 

The Class I antiarrhythmic agents inactivate the fast sodium channel, thereby slowing the movement of Na" across the cell membrane (1,2). This is reflected as a decrease in the rate of development of phase 0 (upstroke) depolarization of the action potential (1,2). The Class I agents have potent local anesthetic effects. These compounds have been further subdivided into Classes lA, IB, and IC based on recovery time from blockade of sodium channels (11). Class IB agents have the shortest recovery times (t1 ) Class lA compounds have moderate recovery times (t 2 usually <9 s) and Class IC have the longest recovery times (t 2 usually >9 s). 

Maintenance of electrical potential between the cell membrane exterior and interior is a necessity for the proper functioning of excitable neuronal and muscle cells. Chemical compounds can disturb ion fluxes that are essential for the maintenance of the membrane potentials. Fluxes of ions into the cells or out of the cells can be blocked by ion channel blockers (for example, some marine tox-... 

This review addresses the issues of the chemical and physical processes whereby inorganic anions and cations are selectively retained by or passed through cell membranes. The channel and carrier mechanisms of membranes permeation are treated by means of model systems. The models are the planar lipid bilayer for the cell membrane, Gramicidin for the channel mechanism, and Valinomycin for the carrier mechanism. 

With the adequacy of lipid bilayer membranes as models for the basic structural motif and hence for the ion transport barrier of biological membranes, studies of channel and carrier ion transport mechanisms across such membranes become of central relevance to transport across cell membranes. The fundamental principles derived from these studies, however, have generality beyond the specific model systems. As noted above and as will be treated below, it is found that selective transport... 

The amiloride-sensitive Na+ channel (ENaC) is a cell membrane glycoprotein selective for sodium ions, which is composed of three subunits (a, (3 and y). Gating of sodium is inhibited by the diuretic amiloride. 

An oligomeric protein that spans a cell membrane forming a regulated pore through which Ca2+ can pass. Ca2+ channels differ considerably in their selectivity for Ca2+ over other cations For example DP3R are poorly selective, voltage-dependent Ca2+ channels are vety selective. 

Non-selective cation channels are macromolecular pores in the cell membrane that form an aqueous pathway. These enable cations such as Na+, K+ or Ca++ to flow rapidly, as determined by their electrochemical driving force, at roughly equal rates (>107 cations per channel pore and per second). 

Non-selective Cation Channels. Figure 1 The nicotinic acetylcholine receptor (nAChR) is localized within the cell membrane above the cell membrane is the synaptic cleft, below the cytoplasm. Drawing of the closed (left) and open (right) nAChR showing acetylcholine (ACh) binding and cation movement. Dimensions of the receptor were taken from references [2, 3]. 

The patch-clamp technique is based on the formation of a high resistance seal (109-10lon) between the tip of a glass micropipette and the cell membrane it touches (gigaohm-seal). This technique allows recordings of ionic currents through single ion channels in the intact cell membrane and in isolated membrane patches at a... 

Potassium channels are a diverse and ubiquitous family of membrane proteins present in both excitable and nonexcitable cells that selectively conduct K+ ions across the cell membrane along its electrochemical gradient at a rate of 106-108 ions/s. 

All these postsynaptic events last only for a few milliseconds synaptic transmission through LGICs is fast. When the postsynaptic cell membrane is sufficiently depolarized, voltage-dependent Na+ channels open and an action potential is generated. 

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