Potassium channel activators electrophysiology

Watson MB, Mahnbei RL (1996) Regulation of Arabidopsis thaliana (L.) Heynh arginine decarboxylase by potassium deficiency stress. Plant Physiol 111 1077-1083 WeigerTM, LangerT, Hermann A (1998) External action of di- and polyamines on maxi calcium-activated potassium channels an electrophysiological and molecular modeling study. Biophys J 74 722-730... 

FIGURE 7.14 Time-course of G-protein-mediated activation of GIRK potassium channels in rabbit sinoatrial node cells, (a). Outward current evoked by a 33-msec, 50-nA iontophoretic pulse of acetylcholine (between arrows), (b). Response of the unclamped cell to an iontophoretic pulse of acetylcholine (ACh). (Record (a) is adapted with permission from Trautwein et al., in Drug Receptors and Their Effectors, Birdsall, N. J. M., Ed., Macmillan, New York, 1980, pp. 5-22 record (b) is adapted with permission from Noma, in Electrophysiology of Single Cardiac Cells, Noble, D. and Powell, T., Eds., Academic Press, San Diego, CA, 1987, pp. 223-246.)... 

A structurally novel series of substituted 10//-benzo[4,5]furo[3,2- ]indole-l-carboxylic acids 504-507 was prepared and shown to possess potent, bladder-selective smooth muscle relaxant properties and thus is potentially useful for the treatment of urge urinary incontinence. Electrophysiological studies using rat detrusor myocytes have demonstrated that prototype compound 8 produces a significant increase in hyperpolarizing current, which is iberiotoxin (IbTx)-reversed, thus consistent with activation of the large-conductance Ca -activated potassium channel (BKca) <2001BML2093>. 

In contrast, amiodarone and sotalol are effective in most supraventricular and ventricular tachycardias. Amiodarone displays electrophysiologic characteristics consistent with each type of antiarrhythmic drug, ft is a sodium channel blocker with relatively fast on-off kinetics, has nonselec-tive j8-blocking actions, blocks potassium channels, and has slight calcium antagonist activity. The impressive effectiveness and low proarrhythmic potential of amiodarone have challenged the notion that selective ion channel blockade is preferable. Sotalol is a potent inhibitor of outward... 

The nervous system is the main site of toxicity for DDT. Effects are observed on both the central nervous system (CNS) and peripherally. There is significant alteration of neuronal membrane enzymatic and electrophysiological properties. In particular, sodium channels are altered such that once activated they close slowly, prolonging the depolarization of the nerve by interfering with the active transport of Na ions out of the axon. Potassium channels are also affected. DDT specifically affects Na", K -adenosine triphosphatases (ATPases) and Ca " -AT-Pases, which inhibit repolarization of neurons. The membrane remains partially depolarized and is extremely sensitive to complete depolarization by very small stimuli. DDT also inhibits calmodulin that is necessary for Ca transport essential for the subsequent release of neurotransmitters. 

Type I antiarrhythmics appear to share a single receptor site in the sodium channel. It should be noted, however, that a number of type I drugs have other electrophysiologic properties. For instance, quinidine has potent potassium channel blocking activity (manifest predominantly at low concentrations), as does A-acetylprocainamide (manifest predominantly at high concentrations), the primary metabolite of procainamide. Additionally, propafenone has /3-blocking actions. 

Prolongation of QT interval may be predicted in vitro by patch clamp electrophysiology in mammalian cells transfected with the human ether-d-go-go-related gene (hERG), a subunit of the (cardiac rapidly activating delayed rectifier potassium channel), or by measuring a compound s abihty... 

The main experimental use of barium is in electrophysiology where it can be used as a charged probe for metal ion-dependent processes. The isolation and identification of individual ion fluxes which contribute to the electric currents flowing through cell membranes often requires techniques to block specific components of electrical activity. This can sometimes be achieved by the use of the soluble salts of divalent cations such as barium and manganese which may block potassium and calcium and currents in, for example, the cardiac pacemaker [4]. Barium can also be used to identify potassium-conducting channels in isolated membrane vesicles [S,6] or calcium charmels in isolated heart muscle cells, myocytes [7], and adrenal gland chromaffin cells [8]. 

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