Potassium channels closure

In addition to the mechanism involving cycHc AMP, nonsugar sweeteners, eg, saccharin and a guanidine-type sweetener, have been found to enhance the production of another second messenger, inositol 1,4,5-trisphosphate (IP3), causing the closure of potassium channels and the release of... 

Mitcheson, J.S., Chen, J. and Sanguinetti, M.C. (2000) Trapping of a methanesulfonanilide by closure of the hERG potassium channel activation gate. The Journal of General Physiology, 115, 229-240. 

The major action of sulfonylureas is to increase insulin release from the pancreas (Table 41-5). Two additional mechanisms of action have been proposed—a reduction of serum glucagon levels and closure of potassium channels in extra pancreatic tissue (which are of unknown but probably minimal significance). 

Synaptic transmission between pairs of neurons in Aplysia (a marine snail) is enhanced by serotonin, a neurotransmitter that is released by adjacent intemeurons. Serotonin binds to a 7TM receptor to trigger an adenylate cyclase cascade. The rise in cAMP level activates PKA, which facilitates the closing of potassium channels by phosphorylating them. Closure of potassium channels increases the excitability of the target cell. 

Fig. 2 Substance P induced NTS plasticity targets in the cough reflex. Plasticity targets include (1) increased intrinsic excitabUity via closure of potassium channels, activation of nonselective cation channels, opening of L-type calcium channel, and intracellular calcium release. (2) increased synaptic excitability via an increased ionotropic glutamate receptor function, a decreased GABAa receptor function. Other compensatory mechanisms may also occur, including an increased GABA release and decreased glutamate release from the afferent terminals. AP area postrema...

Figure 4.20.A shows a more recent cell reported by Cobben et al. It consists of three Perspex blocks, of which two (A) are identical and the third (B) different. Part A is a Perspex block (1) furnished with two pairs of resilient hooks (3) for electrical contact. With the aid of a spring, the hooks press at the surface of the sensor contact pads (4), the back side of which rests on the Perspex siuface, so the sensor gate is positioned in the centre of the block, which is marked by an engraved cross as in the above-described wall-jet cell. Part B is a prismatic Perspex block (2) (85 x 24 x 10 mm ) into which a Z-shaped flow channel of 0.5 mm diameter is drilled. Each of the wedges of the Z reaches the outside of the block. The Z-shaped flow-cell thus built has a zero dead volume. As a result, the solution volume held between the two CHEMFETs is very small (3 pL). The cell is sealed by gently pushing block A to B with a lever. The inherent plasticity of the PVC membrane ensures water-tight closure of the cell. The closeness between the two electrodes enables differential measurements with no interference from the liquid junction potential. The differential signal provided by a potassium-selective and a sodium-selective CHEMFET exhibits a Nemstian behaviour and is selective towards potassium in the presence of a (fixed) excess concentration of sodium. The combined use of a highly lead-selective CHEMFET and a potassium-selective CHEMFET in this type of cell also provides excellent results.

The sulfonylurea receptor was identified as an adenosine triphosphate (ATP) sensitive potassium (Katp) channel that is present on the (3-cell membrane surface. Closure of these K tp channels causes (3-cell membrane... 

The mechanism by which DDT acts is to disturb the function of nerves in the insect. Nerves in both insects and humans work by allowing an electric current to move down them. This action potential, as it is called, depends on the movement of two metal ions, sodium and potassium, across the membrane of the nerve, and involves channels for the sodium being opened very briefly. DDT interacts with the sodium channel in the insect nerve and retards its closure. This means that the flow of sodium and hence the electric current is prolonged and there may be several impulses instead of just one. The function of the nerves thus becomes uncontrolled. This effect of DDT seems to be reversible. 

---