ERYTHROCYTE Ca++, Mg++ ATPase ACTIVITY IN DIABETIC NIGERIANS

Abstract

CA++, Mg++ -ATPase is an important enzyme in CA++ homeostasis. Its activity has been investigated in conditions like hypertension and sickle cell disease. There is no information in the literature on the activity of CA++, Mg++ -ATPase in diabetic Africans. This study was therefore designed to investigate the activity of CA++, Mg++ -ATPase in diabetic Nigerians, The study was carried out in patients attending the university College Hospital (UCH), lbadan with Insulin-dependent Diabetes Mellitus - IDDM (Type I diabetes) and Non-insulin-dependent Diabetes Mellitus - NIDDM (Type 2 diabetes) and Healthy Human volunteers (HHm). The HHm group served as controls. There were 12 subjects in each of the HHm and NIDDM groups and 18 subjects in the HHm group. The subjects were aged 30-65 years. Blood samples (20m1 per subject) were obtained from each subject. Erythrocyte membranes were isolated from the three groups: HHm, IDDM and NIDDM by the method of Niggli et.al.(1981) and their protein concentrations were determined by the method of Lowry et al (1951). The activity of CA++, Mg++ -ATPase in the cell membrane was determined in the presence and absence of calmodulin (CaM) using the method of Stewart (1974). The effects of CA++, Mg++ -ATPase and CaM on the actively Of CA++, Mg++ -ATPase were determined.

The enzyme kinetics of CA++, Mg++ -ATPase were assessed by measuring its KM and Vmax values. Electrophoretic separation of the erythrocyte membrane proteins was carried out to characterize the proteins. The result of the study showed that activity of CA++, Mg++ -ATPase is initiated by adenosine triphosphate (ATP). There ware dose-dependent relationship between CA++, Mg++ -ATPase activity and ATP concentration. Calcium and calmodulin enhanced the activity of the enzyme. The activity of CA++, Mg++ -ATPase was significantly lower in IDDM (1.85± 0.03 nMPi/mgPr/hr.) and NIDDM (1.90± 0.01 nMPi/mgPr/hr.) than in HHm (3.10±0.06 nMPi/mgPr/hr.). There is no significant difference between IDDM and NIDDM. The results suggest a defective calcium translocating mechanism in the diabetic groups. The Km values of IDDM and NIDDM were higher than in healthy humans (HHm) with or without calmodulin. Km of HHm without CaM was 1.0± 0.064mM ATP and with CaM. It was still 1.0± 0.065mM ATP. The Km of NIDDM with and without CaM were 135± 0.025 and 1.34±0.026 mM ATP, respectively. Km for IDDM with and without CaM were 1.31± 0.023 and 1.32±0.022mM ATP, respectively. Km values of most enzymes lie between 10-1 and 10-6mM ATP. The results were discussed and the conclusion from the study, supports the hypothesis that there are alterations in functional status of CA++, Mg++ -ATPase from IDDM and NIDDM and that the high calcium concentration in the cells of IDDM and NIDDM is most likely to be a consequence of reduced CA++, Mg++ -ATPase activity.