title: An ATP-dependent Na+/Mg2+ countertransport is the only mechanism for Mg extrusion in squid axons.
abstract: The components of magnesium efflux in squid axons have been studied under internal dialysis and voltage clamp conditions. The present report rules out the existence of an ATP-dependent, Nao- and Mgo-independent Mg2+ efflux (ATP-dependent Mg2+ pump) leaving the Mg2+-Na+ exchange system as the only mechanism for Mg2+ extrusion. The main features of the Mg2+ efflux are: (1) The efflux is completely dependent on ATP. (2) The efflux can be activated either by external Na+ (forward Mg2+-Na+ exchange) or external Mg2+ (Mg2+-Mg2+ exchange). (3) The mobility of the Mg2+ exchanger in the Na+o-loaded form is greater than that in the Mg2+-loaded one. (4) In variance with the Na+-Ca2+ exchange mechanism, Mg2+-Mg2+ exchange is not activated by external monovalent cations. (5) ATP gamma S replaces ATP in activating Mg2+-Na+ exchange suggesting that a phosphorylation/dephosphorylation process regulates this transport mechanism.
authors.affiliation: Centro de Biofísica y Bioquímica, IVIC, Caracas, Venezuela.
authors.forename: R
authors.initials: R
authors.lastname: DiPolo
authors.forename: L
authors.initials: L
authors.lastname: Beaugé
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000378:metabolism*; D001693:Biological Transport, Active; D049832:Decapodiformes; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism*; D009441:Neurilemma / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
chemical_list: C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D008094:Lithium; D012964:Sodium; D008274:Magnesium