Potassium blocking agents

Haas, H. L. (1984). Histamine potentiates neuronal excitation by blocking a calcium-dependent potassium conductance. Agents Actions 14, 534-7. 

The potassium channel, on the other hand, is blocked by both tetraethylammonium salts (7.3, TEA) and nonyl-triethylammonium (7.4) salts, indicating the presence of a hydrophobic binding site that accommodates the nonyl group. Both blocking agents must be applied intra-axonally, which is understandable if one considers that the K current is always directed outward. 

US Department of Health and Human Services Potassium iodide as a thyroid blocking agent in radiation emergencies. December 2001 (http //www.fda.gov/cder/guidance/index.htm). 

Shleien B, Halperin JA, Bilstad JM, Botstein P, Dutra EV Jr. Recommendations on the use of potassium iodide as a thyroid-blocking agent in radiation accidents an FDA update. Bull NY Acad Med 1983 59(10) 1009-19. 

The 1960s saw the discovery of a number of specific channel-blocking agents. Tetrodotoxin, for example, from the fugu puffer fish, specifically blocks voltagegated sodium channels. This provided very convincing confirmation that the sodium and potassium channels of nerve axons really are separate from each other. It also allowed potassium channels in nerves to be studied on their own, permitted estimates of channel densities in the membrane to be made, and ultimately proved crucial in the biochemical isolation of sodium channels. 

The 1960s and 1970s also saw increasingly sophisticated approaches to the investigation of ion channels in nerve and muscle. Armstrong used quaternary ammonium ions as blocking agents to probe the nature of potassium channels and Hille (1984) measured the permeability of channels to ions of different sizes, and so was able to estimate the minimum dimensions of the channel pore. These indirect... 

The state of the sodium channel varies in healthy ventricular cells and those damaged by ischemia. This variability in the state has implications for antiarrhymic therapy with sodium channel blocking agents. In sick or damaged ventricular cells (i.e., from ischemia or blockade of the sodium/potassium-ATPase [sodium/potassium pump]), the resting membrane is more positive than the healthy resting membrane potential (Figure 12.10). 

Anonymous (1985a) Federal Emergency Management Agency Federal Policy on Distribution of Potassium and Iodide Around Nudear Power Sites for Use as a Thyroidal Blocking Agent. Fed. Regist. 50 (Jun.20) 119 25624-25625. 

Acetylcholine Approximately 5% of brain neurons have receptors for ACh. Most CNS responses to ACh are mediated by a large family of G protein-coupled muscarinic M receptors that lead to slow excitation when activated. The ionic mechanism of slow excitation involves a decrease in membrane permeability to potassium. Of the nicotinic receptors present in the CNS (they are less common than muscarinic receptors), those on the Renshaw cells activated by motor axon collaterals in the spinal cord are the best-characterized. Drugs affecting the activity of cholinergic systems in the brain include the acetylcholinesterase inhibitors used in Alzheimer s disease (eg, tacrine) and the muscarinic blocking agents used in parkinsonism (eg, benztropine). 

The number of transport systems per unit surface area for Na and K ions has been estimated according to the bound amounts of the specific blocking agents—tetrodotoxin and saxytoxiii—as well as by measuring the ionic current fluctuations. For example, a muscle cell membrane contains around 400 sodium transport systems per 1 micron. Conductance of each transport system is about 4 x 10 (for sodium) and 12 x 10" (for potassium). 

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