Protein kinase C downregulation enhanced extracellular Ca21-induced relaxation of isolated mesenteric arteries from aged Dahl salt-sensitive rats

Abstract

The Ca21-sensing receptor (CaSR) detects small changes in extracellular calcium (Ca2e1) concentration ([Ca21]e) and trans-duces the signal into modulation of various signaling pathways. Ca21-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 Ca (PKCa) is a critical regulator of multiple signaling pathways and can phosphory-late 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 PKCa 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 Ca2e1 in wild-type (SS) and CaSR mutant (SS-Casrem1Mcwi) rats. Mutation of the CaSR gene had no significant effect on relaxation. PKCa expression was similar in wild-type and mutant rats, and small-interfering RNA downregulation of PKCa and/or inhibition of PKC with the Ca21sensitive Gӧ 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 PKCa 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 Ca21 sensitivity of the receptor and reversal of age-related changes in vascular tone.