Ca2+-insensitive vascular protein kinase C during pregnancy and NOS inhibition

Abstract

Pregnancy-induced hypertension is associated with increased vascular resistance; however, the cellular mechanisms involved are unclear. We have previously found that the relation between Ca2+ entry and the developed force in vascular smooth muscle is altered during normal pregnancy and in a rat model of pregnancy-induced hypertension produced by long-term treatment with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). The purpose of this study was to investigate whether the pregnancy- associated changes in the vascular Ca2+ entry-force relation reflect changes in the amount and/or activity of Ca2+-insensitive protein kinase C (PKC) isoforms. Active stress and the amount and activity of PKC were measured in deendothelialized aortic strips from nonpregnant and pregnant rats untreated or treated with L-NAME and incubated in Ca2+-free (2 mmol/L EGTA) Krebs solution. In nonpregnant rats, the PKC activator phorbol 12,13- dibutyrate (PDBu, 10-6 mol/L) and the α-adrenergic agonist phenylephrine (Phe, 10-5 mol/L) caused significant, maintained increases in active stress and PKC activity that were inhibited by the PKC inhibitors staurosporine and calphostin C. Western blots in aortic strips of nonpregnant rats revealed the Ca2+-insensitive δ-PKC and ζ-PKC isoforms. Both PDBu and Phe caused translocation of δ-PKC from the cytosolic to the particulate fraction. Compared with nonpregnant rats, the amount of δ-PKC and ζ-PKC and the PDBu- stimulated and Phe-stimulated stress, PKC activity and translocation of δ- PKC were significantly reduced in late pregnant rats but significantly enhanced in pregnant rats treated with L-NAME. The PDBu-induced and Phe- induced responses in nonpregnant rats treated with L-NAME were not significantly different from nonpregnant rats, whereas the responses in pregnant rats treated with L-NAME+L-arginine were not significantly different from pregnant rats. These results provide evidence that a signaling pathway in vascular smooth muscle possibly involving the Ca2+-insensitive δ-PKC and ζ-PKC isoforms is reduced in late pregnancy and enhanced during long- term inhibition of nitric oxide synthesis. The changes in the amount and activity of vascular PKC isoforms may, in part, explain the changes in vascular resistance during normal pregnancy and pregnancy-induced hypertension.