Activatory effect of calcium-binding protein regucalcin on ATP-dependent calcium transport in the basolateral membranes of rat kidney cortex.
The effect of regucalcin, a calcium-binding protein, on ATP-dependent Ca2+ transport in the basolateral membranes isolated from rat kidney cortex was investigated. The prepared membranes were in inside-out oriented and membrane vesicles. Ca(2+)-ATPase activity in the basolateral membranes was progressively elevated by increasing concentrations of regucalcin (10(-8) to 10(-6) M) in the reaction mixture. This increase was dependent on Ca2+ addition. The activatory effect of regucalcin on the enzyme is inhibited by the presence of digitonin (5 x 10(-3)%) which can solubilize the membranous lipids. Moreover, the regucalcin effect was clearly abolished by the presence of vanadate (0.1 mM) or N-ethylmaleimide (5.0 mM). However, the effect of calmodulin (6 x 10(-7) M) to increase Ca(2+)-ATPase activity was not significantly inhibited by vanadate or N-ethylmaleimide, indicating that the action mode of regucalcin differs from that of calmodulin. Also, the activatory effect of regucalcin on Ca(2+)-ATPase was appreciably inhibited by addition of dibutyryl cAMP (10(-5) and 10(-3) M), while inositol 1,4,5-trisphosphate (10(-7) and 10(-5) M) had no effect. Dibutyryl cAMP itself did not have an effect on the enzyme activity. Furthermore, the 45Ca2+ uptake by the basolateral membranes was clearly increased by the presence of regucalcin (10(-7) and 10(-6) M). This increase was completely blocked by the presence of vanadate (0.1 mM), N-ethylmaleimide (5.0 mM) or dibutyryl cAMP (10(-4) and 10(-3) M) in the reaction mixture. These results clearly demonstrate that regucalcin, which is expressed in rat kidney cortex, can increase Ca(2+)-ATPase activity and Ca2+ uptake in the basolateral membranes. Regucalcin may play a cell physiologic role as an activator in the ATP-dependent Ca2+ pumps in the basolateral membranes from rat kidney cortex.
Kurota
H
H
Laboratory of Endocrinology and Molecular Metabolism, Graduate School of Nutritional Sciences, University of Shizuoka, Shizuoka City, Japan.
Yamaguchi
M
M
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002265:Carboxylic Ester Hydrolases; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007672:Kidney Cortex / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D015238:Sulfotransferases
D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D000255:Adenosine Triphosphate; D015238:Sulfotransferases; C028152:alcohol sulfotransferase; D002265:Carboxylic Ester Hydrolases; C513325:Rgn protein, rat; D000251:Adenosine Triphosphatases; D002118:Calcium