Kidney triphosphatase

One in vitro study on rat renal tissue homogenate showed barium weakly inhibited the sodium-potassium-adenosine triphosphatase enzyme system (Kramer et al. 1986). A second study on mouse kidney tubules showed barium chloride could depolarize the membrane and inhibit potassium transport (Volkl et al. 1987). A similar defect in cell membrane transport in humans could be responsible for the renal involvement observed in some cases of acute barium poisoning. 

Three membrane-bound adenosine triphosphatase enzymes have been characterized using Mn(II) and Gd(III) electron paramagnetic resonance (EPR) and a variety of NMR techniques. Mn(II) EPR studies of both native and partially delipidated (Na+ + K+)-ATPase from sheep kidney indicate that the enzyme binds Mn2+ at a single, catalytic site with Kq = 0.21 x 10- M. The X-band EPR spectrum of the binary Mn(II)-ATPase complex exhibits a powder line shape consisting of a broad transition with partial resolution of the 55 n nuclear hyperfine structure, as well as a broad component to the low field side of the spectrum. ATP, ADP, AMP-PNP and Pj all broaden the spectrum, whereas AMP induces a substantial narrowing of the hyperfine lines of the spectrum. 

Sodium pump. This expels Na ions from inside the cell by a mechanism that derives energy from ATP and involves the enzyme adenosine triphosphatase (ATPase). The carrier is linked to the transfer of K" " ions into the cell. The cardiac glycoiides (Chapter 18) act by inliibiting the Na /K" ATPase. Na" and/or CL transport processes in the kidney are inhibited by some diuretics (Chapter 14). 

Postnov, Y.U., Reznikova, M. and Boriskina, G. (1976). Na-K-adenosine triphosphatase in the kidney of rats with renal hypertension and spontaneously hypertensive rats. Pflugers Arch., 362, 95-99... 

Nitric oxide donors [sodium nitroprusside, S-nitroso-N-acetyl-D,L-penicillamine or l-hydroxy-2-oxo-3-(N-methyl-6-aminohexyl)-3-methyl-l-triazene = NOC-9] did not affect the activities of non-specific alkaline phosphatase and non-specific esterase in rat and mouse kidney proximal tubulo-cytes which do not contain nitric oxide synthase I (Dahrmann etal. 1997). However, the activities of succinate dehydrogenase (EC 1.3.99.1), cytochrome c oxidase (EC 1.9.3.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), and cholinesterase (EC 3.1.1.7) and different types of adenosine triphosphatase (EC 3.6.1.3) were found reduced. 

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