Electrical excitability and ion channels

MYELIN FORMATION, STRUCTURE AND BIOCHEMISTRY 51 MEMBRANE TRANSPORT 73 ELECTRICAL EXCITABILITY AND ION CHANNELS 95 CELL ADHESION MOLECULES 111 THE CYTOSKELETON OF NEURONS AND GLIA 123... 

Taste cells have multiple types of ion channels. TRCs are electrically excitable and capable of generating action-potentials voltage-dependent channels for Na+, Ca2+ and K+, similar to those in neurons, have been detected in vertebrate TRCs. The surface distribution of these channels... 

Researchers at the MoneU Center (Philadelphia, Pennsylvania) are using a variety of electrophysical and biochemical techniques to characterize the ionic currents produced in taste and olfactory receptor cells by chemical stimuli. These studies are concerned with the identification and pharmacology of the active ion channels and mode of production. One of the techniques employed by the MoneU researchers is that of "patch clamp." This method aUows for the study of the electrical properties of smaU patches of the ceU membrane. The program at MoneU has determined that odors stimulate intraceUular enzymes to produce cycUc adenosine 3, 5 -monophosphate (cAMP). This production of cAMP promotes opening of the ion channel, aUowing cations to enter and excite the ceU. MoneU s future studies wiU focus on the connection of cAMP, and the production of the electrical response to the brain. The patch clamp technique also may be a method to study the specificity of receptor ceUs to different odors, as weU as the adaptation to prolonged stimulation (3). 

Ion Channels. The excitable cell maintains an asymmetric distribution across both the plasma membrane, defining the extracellular and intracellular environments, as well as the intracellular membranes which define the cellular organelles. This maintained a symmetric distribution of ions serves two principal objectives. It contributes to the generation and maintenance of a potential gradient and the subsequent generation of electrical currents following appropriate stimulation. Moreover, it permits the ions themselves to serve as cellular messengers to link membrane excitation and cellular... 

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-... 

While many biological molecules may be targets for oxidant stress and free radicals, it is clear that the cell membrane and its associated proteins may be particularly vulnerable. The ability of the cell to control its intracellular ionic environment as well as its ability to maintain a polarized membrane potential and electrical excitability depends on the activity of ion-translocating proteins such as channels, pumps and exchangers. Either direct or indirect disturbances of the activity of these ion translocators must ultimately underlie reperfiision and oxidant stress-induced arrhythmias in the heart. A number of studies have therefore investigated the effects of free radicals and oxidant stress on cellular electrophysiology and the activity of key membrane-bound ion translocating proteins. 

The electrical oscillations at the aqueous-organic interface or at membranes in the absence of any substances relative to the channel or gate were introduced. These oscillations might give some fundamental information on the electrical excitability in living organisms. Since the ion transfer at the aqueous-organic or aqueous-membrane interface and the interfacial adsorption are deeply concerned in the oscillation, it has been stressed that the voltammetry for the ion transfer at an interface of two immiscible electrolyte solutions is... 

Albuquerque, E.X. Warnick, J.E. Aguayo, L.G. Ickowicz, R.K. Blaustein, M.P. Maayani, S. and Weinstein, H. Phencyclidine Differentiation of behaviorally active from inactive analogs based on interactions with channels of electrically excitable membranes and of cholinersic receptors. In Kamenka, J.M. Domino, E.F. and Geneste P., eds. Phencvclidine and Related Arvl hexvl ami nes Present and Future Appl i cat ions. Ann Arbor ... 

Figure 12.6 Mechanism of action of mineralocortjcoid receptor antagonists in the collecting tubule. Aldosterone enters the tubular cell by the basolateral surface and binds to a specific mineralocorticoid receptor (MNR) in the cytoplasm. The hormone receptor complex triggers the production of an aldosterone-induced protein (AlP) by the cell nucleus (NUC). The AIP acts on the sodium ion channel (ic) to augment the transport of Na+across the basolateral membrane and in to the cell. An increase in AIP activity leads to the recruitment of dormant sodium ion channels and Na pumps (P) in the cell membrane. AIP also leads to the synthesis of new channels and pumps within the cell. The increase in Na+conductance causes electrical changes in the luminal membrane that favour the excretion of intracellular cations, such as K+and H-h. Spironolactone competes with aldosterone for the binding site on the MNR and forms a complex which does not excite the production of AIP by the nucleus.

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