Calmodulin levels and divalent cation pump activities in kidneys of streptozotocin-diabetic rats.

Levels of calmodulin and activities of calcium and magnesium ATPases were determined in renal tissues of age-matched male rats after increasing durations of the following conditions: untreated streptozotocin (STZ) induced diabetes; STZ-diabetic rats which received daily insulin (NPH) treatment beginning 24 hours after STZ administration; and STZ-diabetic rats which began receiving NPH after having endured untreated diabetes for 1, 2, and 3 weeks. Results were compared with those of age-matched control animals. Calmodulin levels were the same in renal tissues from all groups of rats as were magnesium-ATPase activities. Calcium-ATPase activities were significantly higher than control activities after 2 weeks of untreated STZ-diabetes and in tissues from all rats that received insulin treatment which was instituted after 1, 2 and 3 weeks of STZ-diabetes. Calcium ATPase activities of tissues from rats which received insulin treatment 24 hrs after STZ injections were no different from control values. The data indicate that prolonged deficiency of insulin results in insufficient passive transport of calcium from urine into tubular cells. Thus, the increased activity of calcium-ATPase on the contraluminal membrane of kidney cells represents a futile attempt to conserve calcium.