Protein Kinase C Downregulation Enhanced Extracellular Ca2+-Induced Relaxation of Isolated Mesenteric Arteries from Aged Dahl Salt-Sensitive Rats

The Ca2+-sensing receptor (CaSR) detects small changes in extracellular calcium (Ca-e(2+)) concentration ([Ca2+](e)) and transduces the signal into modulation of various signaling pathways. Ca2+-induced relaxation of isolated phenylephrine-contracted mesenteric arteries is mediated by the CaSR of the perivascular nerve. Elucidation of the regulatory mechanisms involved in vascular CaSR signaling may provide insights into the physiologic functions of the receptor and identify targets for the development of new treatments for cardiovascular pathologies such as hypertension. Protein kinase C alpha (PKC alpha) is a critical regulator of multiple signaling pathways and can phosphorylate the CaSR leading to receptor desensitization. In this study, we used automated wire myography to investigate the effects of CaSR mutation and small-interfering RNA downregulation of PKC alpha on CaSR-mediated relaxation of phenylephrine-contracted mesenteric arteries from aged Dahl salt-sensitive (SS) rats on a low-salt diet. The data showed minimal relaxation responses of arteries to Ca-e(2+) in wild-type (SS) and CaSR mutant (SS-Casr(em1Mcwi)) rats. Mutation of the CaSR gene had no significant effect on relaxation. PKC alpha expression was similar in wild-type and mutant rats, and small-interfering RNA down-regulation of PKC alpha and/or inhibition of PKC with the Ca2+-sensitive Go 6976 resulted in a >80% increase in relaxation. Significant differences in EC50 values were observed between treated and untreated controls (P < 0.05 analysis of variance). The results indicate that PKC alpha plays an important role in the regulation of CaSR-mediated relaxation of mesenteric arteries, and its downregulation or pharmacological inhibition may lead to an increased Ca-2(+) sensitivity of the receptor and reversal of age-related changes in vascular tone. SIGNIFICANCE STATEMENT G protein-coupled CaSR signaling leads to the regulation of vascular tone and may, therefore, play a vital role in blood pressure regulation. The receptor has several PKC phosphorylation sites in the C-terminal intracellular tail that mediate desensitization. We have previously shown that activation of the CaSR in neuronal cells leads to PKC phosphorylation, indicating that protein kinase C is an important regulator of CaSR function. Therefore, PKC in the CaSR signaling pathway in mesenteric arteries is a potential target for the development of new therapeutic approaches to treat hypertension and age-related vascular dysfunction. The present studies show that small-interfering RNA downregulation of PKC alpha and pharmacological inhibition of PKC enhanced CaSR-mediated relaxation of phenylephrine-contracted mesenteric arteries from aged Dahl salt-sensitive rats.