UNCOUPLING BY TREHALOSE OF CA2-MEMBRANE (CA2++MG2+)ATPASE OF KIDNEY-TUBULES( TRANSPORT AND ATP HYDROLYSIS BY THE PLASMA)

Trehalose, the disaccharide of glucose, inhibits both initial rate and maximal capacity of ATP-dependent Ca2+ transport in inside-out vesicl es of basolateral membrane from kidney proximal tubules. This inhibiti on (I-0.5 = 60 mM) cannot be attributed to an increase in Ca2+ permeab ility, since the rate of EGTA-stimulated Ca2+ efflux from preloaded ve sicles is not modified by trehalose. In the presence of 600 mM trehalo se, Ca2+ uptake was almost completely inhibited, but the Ca2+-stimulat ed ATPase activity was unaffected; thus trehalose uncouples the Ca2+ t ransport from the ATPase activity. The Ca2+ transport inhibition by tr ehalose is reversible, since the inhibition disappeared when the vesic les were pre-incubated with 600 mM trehalose and then diluted in react ion medium to measure Ca2+ accumulation. Other mono- and disaccharides such as glucose, fructose, galactose, sucrose, maltose and lactose we re tested but were not so effective as trehalose. The uncoupling of Ca 2+ transport from hydrolysis can be explained by an interaction of tre halose with the phospholipid environment of the enzyme that induces co nformational changes in specific domains of the enzyme so as to impair the coupling process.