Calcium-atpase activity in cystic fibrosis erythrocyte membranes: Decreased activity in patients with pancreatic insufficiency

The activity of Ca-ATPase (Ca²⁺, Mg²⁺-ATPase, ATP phosphohydrolase, EC 3.6.1.3) was measured in erythrocyte membrane preparations from 37 cystic fibrosis patients, 27 with pancreatic insufficiency and 10 with pancreatic sufficiency, from 24 healthy controls. The mean maximal calcium-stimulated specific activities, in the absence and presence of purified calmodulin, of the pancreatic sufficient patients (34.3 ± 4.2 and 75.9 ± 6.9 nmol/min/mg) was indistinguishable from that of controls (35.8 ± 2.6 and 84.3 ± 4.7 nmol/min/mg), while both activities of patients with pancreatic insufficiency were significantly decreased (28.9 ± 1.3, p <0.02; 65.2 ± 3.0, p <0.001) compared to the control group. Similarly, the mean erythrocyte membrane (Na + K)ATPase activity was decreased only for those patients with a history of steatorrhea and who clinically required pancreatic enzyme therapy and had low immunoreactive trypsin levels (10.6 ± 0.8 versus control, 13.4 ± 1.1, and pancreatic sufficient patients, 13.3 ±1.4 nmol/min/mg; p <0.025). No correlation was found between any of the ATPase activities and the clinical scores of the patients, suggesting the lack of significant contribution of general clinical status to the activities of those cation transporters.