Active Ca Transport of Sarcoplasmic Reticulum during Experimental Uremia. Changes in Kinetics and Lipid Composition

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Abstract
The Ca-transport system of sarcoplasmic vesicles of rabbits is altered by experimental uremia. 1 The influx rate constant of the experimental membranes decrease with a resulting decrease of the calcium influx rate. 2 The experimental membranes transport a smaller amount of Ca2+ per mol of ATP split than the controls, i.e. their transport ratio is decreased. 3 The calcium permeability of the experimental membranes increases with a resulting decreased concentrating ability. 4 The phosphatide content but not the cholesterol content of the experimental membranes decreases with a consequent increase of the cholesterol/phosphatide ratio. 5 The fatty acid pattern of total phosphatides of the experimental membranes changes. A relative decrease of palmitic acid and oleic acid occurs and a relative increase of stearic, arachidonic and higher unsaturated fatty acids. 6 The altered lipid composition of the membranes does not change the temperature dependence of the kinetics.