A high‐affinity, calmodulin‐dependent Ca2+ pump in the basal‐lateral plasma membranes of kidney cortex

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Abstract
A purified preparation of kidney basolateral membrane vesicles is capable of ATP-dependent Ca2+ uptake. The reaction has high affinity for Ca2+ (Km about 0.1 μM) and a V of 5.8 nmol Ca2+× mg−1 protein × min−1 in the predominantly right-side-out vesicular preparation used. It is inhibited by vanadate (K0.5 about 5 μM) and by anticalmodulin drugs. A stimulatory effect of calmodulin is visible in membranes depleted of the activator. Exposure of basolateral membranes to 125I-azido-modified calmodulin results in the specific labeling of a membrane protein of Mr 141 000, which is tentatively suggested to be the Ca2+-pumping ATPase.