ATP-driven Ca2+ pump in the basolateral membrane of rat kidney cortex catalyzes an electroneutral Ca2+/H+ antiport

An ATP-driven Ca2+ pump in the basolateral membrane of rat kidney cortex pumps Ca2+ out of the cell at the expense of MgATP (Km = 0.191 mM). This pump has a high affinity for free Ca2+ (26 nM). Vanadate, lanthanum, N-ethylmaleimide and calmodulin inhibitor R24571 inhibited this pump activity. Dimethyl[2-14C]oxazolidine-2,4-dione [( 14C]DMO) was entrapped in the vesicles in association with the ATP-driven Ca2+ influx. The ATP-driven Ca2+ influx was stimulated by the intravesicular acid pH and an upper convex Lineweaver-Burk reciprocal plot suggested two possible kinetics; one is that this Ca2+ pump is an allosteric enzyme with more than 1.72 H+ binding sites and another is the presence of two Ca2+ pumps with different affinities for H+. Valinomycin study indicated that the ATP-dependent Ca2+ transport by the BLMV was electroneutral and voltage independent. These results strongly suggest that the ATP-driven Ca2+ pump in the renal basolateral membrane catalyzes an electroneutral Ca2+/H+ antiport.