Role of the PKC/CPI-17 pathway in enhanced contractile responses of mesenteric arteries from diabetic rats to α-adrenoceptor stimulation

I Protein kinase C (PKC) may contribute to enhanced contractile responses of arteries from streptozotocin-diabetic rats to stimulation of G-protein coupled receptors. This was investigated by comparing the effects of PKC inhibitors on contractile responses of mesenteric arteries from diabetic and age-matched control rats to noradrenaline (NA) and endothelin-1 (ET-1). The effects of NA and ET-1 on the distribution of three isoforms of PKC implicated in contraction were also determined. In addition, the effect of NA on phosphorylation of CPI-17, a substrate for PKC, was investigated. 2 Contractile responses of endothelium-denuded arteries from diabetic rats to NA were enhanced, but were normalized by PKC inhibition. In contrast, contractile responses to ET-1 were not significantly different, and were blocked to a similar extent by PKC inhibition, in arteries from control and diabetic rats. 3 NA produced only a small increase in particulate levels of PKC epsilon in control arteries (to 125 +/- 8% of levels in untreated arteries), but a significant increase in particulate PKC alpha (to 190 +/- 22%) and a much greater increase in particulate PKCe (to 230 +/- 19%) in arteries from diabetic rats. ET-1 increased particulate PKC alpha and epsilon to a similar extent in arteries from control and diabetic rats. 4 NA significantly enhanced CPI-17 phosphorylation from a basal level of 22 +/- 10 to 71 +/- 7% of total in arteries from diabetic rats, and this was prevented by PKC inhibition. NA had no detectable effect on CPI-17 phosphorylation in arteries from control rats. 5 These data suggest that NA-induced activation of PKC and CPI-17, its downstream target, is selectively enhanced in arteries from diabetic rats, and mediates the enhanced contractile responses to this agonist.