Excitability is an attribute of life, and is a driving force in the descent of complexity. Cellular electrical activity as realized by membrane proteins that act as either channels or transporters is the basis of excitability. Electrical signaling is mediated by a wave of action potentials, which consist of synchronous redistribution of ionic gradients down ion channels. Ion channels select for...

In order to characterize a step in the reaction sequence of sodium and potassium ion-dependent adenosine triphosphatase (EC 3.6.1.3), the binding of radioactive adenosine triphosphate to kidney cell membranes was estimated by flow dialysis in the presence of a chelator of divalent cations, which prevented hydrolysis of the adenosine triphosphate. Adenosine triphosphate was bound to a single sit...

We established a simple and rapid enzymatic method for measuring potassium ion in serum by using tryptophanase (EC 4.1.99.1) purified from Escherichia coli K12 strain (E. coli K12 IFO 3301). The presence of pyridoxal 5-phosphate promotes this enzymatic reaction, and potassium and (or) ammonium ions further accelerate it, with ammonium and potassium ions providing equivalent acceleration. We eli...

Analysis of ion channel mutants is a widely used approach for dissecting ion channel function and for characterizing the mechanisms of action of channel-directed modulators. Expression of functional potassium channels in potassium-uptake-deficient yeast together with genetic selection approaches offers an unbiased, high-throughput, activity-based readout that can rapidly identify large numbers ...

potassium channels allow potassium flux and are essential for the generation of electric current acrossexcitable membranes. potassium channels are also the targets of various intracellular controlmechanisms; such that the suboptimal regulation of channel function might be related to pathologicalconditions. realistic studies of ion current in biologic channels present a major challenge for compu...

We have used ion-selective electrodes (ISEs) to quantify ion fluxes across giant membrane patches by measuring and simulating ion gradients on both membrane sides. Experimental conditions are selected with low concentrations of the ions detected on the membrane side being monitored. For detection from the cytoplasmic (bath) side, the patch pipette is oscillated laterally in front of an ISE. For...

1. The non-radioactive cesium ion can replace the potassium ion almost quantitatively in solutions required for the development of the egg of the sea urchin into swimming blastulae. 2. Thorium chloride and uranium acetate cannot replace the potassium chloride in the solutions required for the development of the egg. 3. Thorium chloride and uranium acetate do not antagonize the action of the pot...

Physiological ligands of (sodium-potassium)-dependent adenosine triphosphatase influenced the sensitivity of the enzyme to the inhibitor, ouabain. Phosphorylation of the native enzyme is accelerated by sodium ions, while potassium ions accelerate dephosphorylation. Exposure of the phosphoenzyme to ouabain slowed its turnover and rendered it insensitive to potassium ion. This action of ouabain d...

The injection of tetraethylammonium chloride into the giant axon of the squid prolongs the action potential and eliminates most of the late current under voltage-clamp. Experiments on fibers in an external medium of high potassium ion concentration demonstrate that injected tetraethylammonium chloride causes rectification of the instantaneous current-voltage curve for potassium by excluding out...

After a 20 min initial washout, the rate of loss of radioactively labeled sodium ions from sodium-enriched muscle cells is sensitive to the external sodium and potassium ion concentrations. In the absence of external potassium ions, the presence of external sodium ions increases the sodium efflux. In the presence of external potassium ions, the presence of external sodium ions decreases the sod...