Calcium-dependent protein kinase activity is decreased in diabetic rat sciatic nerve

The effects of 4 weeks of streptozotocin-induced diabetes in the rat on sciatic nerve homogenate protein kinase activities were studied. There was a 47 +/- 7% inhibition of Ca+2-dependent protein kinase activity in nerves from the diabetic rats compared to that in their paired normal controls. This Ca+2-dependent activity did not require the addition of phospholipid and was only minimally affected by Sephadex G-50 gel filtration, suggesting that endogenous phospholipid activation was not responsible for this activity. The addition of phospholipid in the presence of Ca+2 revealed an additional activity in these homogenates which probably represents the Ca+2-phospholipid-dependent protein kinase (protein kinase-C). The diabetic state did not appear to alter that activity. The Ca+2-dependent protein kinase was sensitive to agents known to inhibit calmodulin-dependent protein kinase or protein kinase-C. The IC50 values of the inhibitors for the Ca+2-dependent protein kinase, however, differed from those reported for the other two kinases.