Rice (Oryza sativa; background Nipponbare) contains nine HKT (high-affinity K+ transport)-like genes encoding membrane proteins belonging to the superfamily of Ktr/TRK/HKT. OsHKTs have been proposed to include four selectivity filter-pore-forming domains homologous to the bacterial K+ channel KcsA, and are separated into OsHKT1s with Na+-selective activity and OsHKT2s with Na+-K+ symport activi...

effects of atp and mg2+ concentrations on bioluminescence reaction of luciferase (photinus pyralis) were investigated by home-made luminometer. the michaelis constants of the enzyme for atp and mg2+ obtained from the lineweaver-burk graph, were 61.9 mm ±3.3 mm and 251.6mm ± 39.0mm respectively. optimum concentration of mg2+ for maximum luminescence was 0.004 m.

Voltage-dependent channel block by external Mg2+ (Mg2+(o)) of NMDA receptors is an essential determinant of synaptic function. The resulting Mg2+(o) inhibition of NMDA responses depends strongly on receptor subunit composition: NR1/2A and NR1/2B receptors are more strongly inhibited by Mg2+(o) than are NR1/2C or NR1/2D receptors. Previous work showed that permeant ions have profound effects on ...

This study is concerned with the regulation of intracellular-free Mg2+ concentration ([Mg2+]i) in the smooth muscle of guinea pig taenia caeci. To assess an interaction of Ca2+ on the Na(+)-dependent Mg(2+)-extrusion mechanism (Na(+)-Mg2+ exchange), effects of Na+ removal (N-methyl-D-glucamine substitution) were examined in Ca(2+)-containing solutions. As changes in pHi in Na(+)-free solutions ...

Total Mg2+ content in plasma and erythrocytes did not significantly differ between WKY and SHR. Mg2+ efflux via Na+/Mg2+ antiport was 10% lower in non Mg(2+)-loaded erythrocytes of SHR than in WKY, and 16% lower in Mg(2+)-loaded erythrocytes of SHR. The activation of Na+/Mg2+ antiport in erythrocytes by Cl-, as tested by substitution of Cl- with SCN-, and the regulation of Na+/Mg2+ antiport by ...

Metabolic and functional responses to extracellular Mg2+ concentration ([Mg2+]o) were studied in perfused rat heart. Elevations of [Mg2+]ofrom 1.2 to 2.4, 5.0, and 8.0 mM dose dependently reduced contractile function and myocardial oxygen consumption (MV˙o 2) up to 80%. Intracellular Mg2+ concentration ([Mg2+]i) remained stable (0.45-0.50 mM) during perfusion with 1.2-5.0 mM [Mg2+]obut increase...

Mg2+-extrusion from Mg2+-loaded neurons of the leech, Hirudo medicinalis, is mediated mainly by Na+/Mg2+ antiport. However, in a number of leech neurons, Mg2+ is extruded in the nominal absence of extracellular Na+, indicating the existence of an additional, Na+-independent Mg2+ transport mechanism. This mechanism was investigated using electrophysiological and microfluorimetrical techniques. T...

In excitable cells, the concentration of intracellular free Mg2+ ([Mg2+]i) is several hundred times lower than expected if Mg2+ ions were at electrochemical equilibrium. Since Mg2+ is a permeant ion across the plasmalemma, it must be constantly extruded. An ATP-dependent Na/Mg exchanger has been proposed as the sole mechanism responsible for Mg2+ extrusion. However, this hypothesis fails to exp...

Glucagon and arginine vasopressin (AVP) enhance renal magnesium conservation through actions within the loop of Henle and the distal tubule. Studies were performed on an immortalized mouse distal convoluted tubule (MDCT) cell line to characterize the cellular actions of these hormones on Mg2+transport in this segment of the distal tubule. Glucagon and AVP increased cellular cAMP concentrations ...

Mammalian cells tightly regulate cellular Mg2+ content despite undergoing a variety of hormonal and metabolic stimulatory conditions. Evidence from several laboratories indicates that stimulatory conditions that increase cellular cAMP level result in a major mobilization of Mg2+ from cells and tissues into the bloodstream. Conversely, hormones or agents that decrease cAMP level or activate prot...