Role of protein kinase C in superoxide production by the renal medullary thick ascending limb from normal and diabetic rats

Accelerated O 2 ·− production by the medullary thick ascending limb (mTAL) occurs during type 1 diabetes (T1D), and T1D activates protein kinase C (PKC) in a variety of tissues. The purpose of this study was to test the hypothesis that T1D‐induced PKC activation contributes to O 2 ·− production in the mTAL and to determine which PKC isoform(s) are involved. O 2 ·− production (lucigenin chemiluminescence) by mTAL suspensions prepared from normal rats ( n =6) averaged 426±26 RLU/sec/mg protein in 5.5 mM glucose media. Incubation 30 min in either 1 μM Calphostin C (pan‐specific PKC inhibitor), 1 μM Gö6976 (PKC α & β inhibitor) or 10 μM Rottlerin (PKC δ inhibitor) significantly decreased O 2 ·− production to 11±3, 17±3 or 2±1 % of baseline, respectively. PKC inhibitors had similar effects in normal mTALs exposed to 20 mM glucose for 30 min. mTAL suspensions from rats with streptozotocin‐induced T1D (STZ rats, 3–4 wk after onset; n =6) were prepared and studied in 20 mM glucose to maintain the chronic in vivo condition of the donor rats. O 2 ·− production was 2668±553 RLU/sec/mg in STZ mTALs ( P <0.05 vs normal mTALs) and significantly decreased to 9±2, 12±3 or 2±1 % of baseline, respectively, upon treatment with Calphostin C, Gö6976, or Rottlerin. We conclude that PKC activity is required for O 2 ·− production by mTALs from normal and diabetic rats, and that multiple PKC isoforms (α and/or β, as well as δ) are involved in this process.