Regulation of the (Ca(2+)+Mg2+)-ATPase of basolateral membranes from kidney proximal tubules by kinase-mediated phosphorylation and by insulin.
Membrane vesicles derived from the basolateral aspect of kidney proximal tubule cells are phosphorylated by ATP in the absence of Ca2+. This Mg(2+)-dependent, hydroxylamine-resistant phosphorylation was associated with a 50% inhibition of the (Ca(2+)+Mg2+)-ATPase activity measured upon addition of micromolar Ca2+ concentrations, enough to saturate the high-affinity sites of the Ca2+ pump. The presence of either the protein kinase inhibitor H7 or insulin during phosphorylation virtually eliminated the inhibitory effect associated with phosphorylation. However, insulin itself inhibited ATP hydrolysis by the (Ca(2+)+Mg2+)-ATPase when it was present in the assay medium containing buffer, ATP, Mg2+ and Ca2+, the hydrolytic activity being initiated by addition of the membranes without prior phosphorylation. These results suggest that insulin may play a role in regulating transepithelial Ca2+ transport in renal proximal tubules, and that its effects may be linked with a kinase-mediated process that depends on the functional state of the (Ca(2+)+Mg2+)-ATPase.
Guilherme
A
A
Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brazil.
Reis-Silva
C
C
Vieyra
A
A
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D006898:Hydroxylamines / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D007546:Isoquinolines / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000201:enzymology*; D010764:Phosphorylase Kinase / Q000502:physiology*; D010879:Piperazines / Q000494:pharmacology; D011487:Protein Conformation; D047428:Protein Kinase Inhibitors; D017433:Protein Structure, Secondary; D012756:Sheep
D006898:Hydroxylamines; D007328:Insulin; D007546:Isoquinolines; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D010764:Phosphorylase Kinase; D017301:Ca(2+) Mg(2+)-ATPase