Calcium transport by basolateral membranes of diabetic rats

The current study was designed to examine calcium transport across the basolateral membrane of the enterocyte of control and diabetic rats. The slope of initial rate of ATP-dependent calcium uptake was significantly greater in controls than in diabetic rats (P < 0.001). Kinetic analysis of ATP-dependent calcium uptake showed a maximum velocity (V_max) of 0.19 ± 0.02 and 0.37 ± 0.01 μmol · g protein^-1 · s^-1 in diabetic and control rats, respectively (P < 0.01). K_m values were similar. Insulin therapy and calmodulin added to freeze-thawed basolateral membranes vesicles stimulated V_max of ATP-dependent calcium uptake in diabetic membranes to values close to those of controls without a change in K_m values. In contrast, the Ca⁺⁺-Na⁺ exchange process was similar in both control and diabetic rats. These results suggest that the ATP-dependent calcium uptake process is decreased in diabetic animals. This decrease is stimulated by calmodulin or insulin therapy, implying a causal relationship between insulin deficiency and calmodulin activity in diabetes.