Guilherme A, Reis-Silva C, Vieyra A
Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brazil.
Acta Physiol Scand Suppl. 1992;607:223-7.
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.
源自肾近端小管细胞基底外侧的膜囊泡在无Ca2+的情况下被ATP磷酸化。这种依赖Mg(2+)、对羟胺耐受的磷酸化与加入微摩尔浓度Ca2+（足以饱和Ca2+泵的高亲和力位点）后测得的（Ca(2+)+Mg2+）-ATP酶活性50%的抑制相关。磷酸化过程中蛋白激酶抑制剂H7或胰岛素的存在实际上消除了与磷酸化相关的抑制作用。然而，当胰岛素存在于含有缓冲液、ATP、Mg2+和Ca2+的测定介质中时，它自身会抑制（Ca(2+)+Mg2+）-ATP酶的ATP水解，水解活性通过加入未经预先磷酸化的膜来启动。这些结果表明，胰岛素可能在调节肾近端小管的跨上皮Ca2+转运中起作用，并且其作用可能与依赖于（Ca(2+)+Mg2+）-ATP酶功能状态的激酶介导过程有关。
