MgATP and phosphoinositides activate Na(+)/Ca(2+) exchange in bovine brain vesicles. Comparison with other Na(+)/Ca(2+) exchangers.

We investigated the metabolic modulation of the Na(+)/Ca(2+) exchanger in membrane vesicles obtained from bovine brain. The Na(+)/Ca(2+) exchanger was activated by MgATP with a K(0.5) of 336 micro M. Unlike the squid nerve Na(+)/Ca(2+) exchanger, this effect required no cytosolic component. Also, stimulation is the same in vesicles prepared and/or assayed at the ionic strength found in mammals (160 mM) or marine animals (300 mM). Other differences between squid and bovine nerve are that the bovine brain Na(+)/Ca(2+) exchanger is not stimulated by phosphagens, either phosphoarginine (molluscan source) or phosphocreatine (mammalian source); and that stimulation by MgATP in bovine brain is related to the production of polyphosphatidylinositides. In this regard bovine heart and brain Na(+)/Ca(2+) exchangers behave similarly. These results indicate that the mechanisms of metabolic regulation of the squid and mammalian nerve Na(+)/Ca(2+) exchangers are not alike and represent differences between species. Some differences found between bovine heart and brain exchangers, such as MgATP stimulation even at saturating [Ca(2+)] and the smaller degree of activation by adenosine 5'- O-(3-thiotriphosphate) (ATP-gamma-S) in the brain, may be related to the unequal isoform population in both tissues.