Calcium pump activity of the renal plasma membrane and renal microsomes |
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Authors: | Leon Moore David F Fitzpatrick Teresa S Chen Erwin J Landon |
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Institution: | Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tenn. 37232 U.S.A. |
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Abstract: | ATP-dependent Ca2+ uptake distinct from that of the mitochondria is found in both plasma membrane and microsomal membranes of rat kidney. Activity attributed to these fractions is enhanced by ammonium oxalate and is apparently insensitive to NaN3. In contrast, rat kidney mitochondrial Ca2+ uptake is blocked by NaN3. The pH of optimal activity is significantly higher for the mitochondrial fraction. Microsomal membrane Ca2+ uptake differs from that of the plasma membrane. Microsomal membranes are four times as active as the plasma membrane at high (5 mM) ATP levels. Apparent Km values for Mg2+-ATP differ in the two preparations with a higher affinity for Mg2+-ATP found in the plasma membrane Ca2+ uptake activity of the plasma membrane preparation is readily inhibited by Na+. Sucrose gradient density fractionation indicates that the observed microsomal membrane Ca2+ pump activity is associated with membrane vesicles derived from the endoplasmic reticulum. Ca2+ pump activity of both plasma membrane and microsomal fraction is depressed din the adrenalectomized rat. This activity is not restored by a single natriuretic dose of aldosterone. |
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Keywords: | SITS 4-acetamido-4′-isothiocyanostilbene-2 2′-disulphonic acid |
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