Abstract
1. Cellular membranes were obtained by centrifugation of homogenates of various human and guinea-pig tissues. These membranes took up added calcium (Ca) when incubated at 25 degrees C for 10 min in histidine buffer at pH 7.4. The uptake of Ca was increased by the presence of adenosine triphosphate (ATP).2. Evidence is presented that the membrane fragments which took up Ca under these conditions were derived from the endoplasmic reticulum.3. The ATP-dependent uptake of Ca by membranes derived from guinea-pig aortic or gastric smooth muscle or from human umbilical arterial muscle was inhibited by indomethacin in a concentration-dependent manner.4. The ATP-dependent uptake of Ca by membranes derived from heart, brain, skeletal muscle or liver of the guinea-pig was not inhibited by indomethacin.5. Endothelial cells were obtained from the lining of the human umbilical vein. Cellular membranes were prepared from the endothelial cells by homogenization and centrifugation. The endothelial membranes took up added Ca in the presence of added ATP and this uptake was inhibited by indomethacin and also by members of a group of pharmacologically-related drugs.