“…However, despite numerous investigations it is not clear which ATPase activity in proximal tubules and in isolated brush-border membrane vesicles reflects the H+-ATPase. The "Mg2+-ATPase '' measured in cortex homogenates [45], microdissected nephrons [32], and isolated brush-border membranes [5,20,31,44] is stimulated by Ca ~-+ and other nucleotides besides ATP [13,31,44,45], This pattern is typical for ecto-ATPases found in other cells [14,18,28,29,40,42] rather than for an ATPase involved in H + transport. The "bicarbonate-stimulated ATPase" in a rat kidney brush-border membrane preparation was related to ATP-driven H+se -cretion [35,36,41,43], but was later shown to be of mitochondrial origin [13,31,38].…”